Signal processing device and radar system

Abstract

To provide a technique capable of removing an interference component in a wider frequency domain when removing the interference component included in a beat signal in the frequency domain.SOLUTION: A signal processing device 200 performs Fourier transformation of a beat signal Bw of a time domain to a first signal Bwf1 of a frequency domain in which a frequency component is expressed for each frequency bin, executes adaptive processing of outputting an output signal based on a main input signal and a reference input signal by using each positive frequency component of a first signal sequentially as the main input signal of an adaptive filter 221 and using each corresponding negative frequency component sequentially as the reference input signal of the adaptive filter, executes FIR filter processing of processing the reference input signal by an FIR filter 222 in the adaptive processing, output processing of outputting a residual between the main input signal and the reference input signal processed by the FIR processing as the output signal, and update processing of updating a tap coefficient on the basis of the residual, and changes a step size parameter for updating the tap coefficient on the basis of the bin number.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a signal processing device and a radar system. [Background technology]

[0002] In a radar system that measures a target based on a beat signal obtained by mixing a transmission signal transmitted as an electromagnetic wave to the target with a received signal obtained by receiving the electromagnetic wave reflected by the target, an interference signal may occur in the beat signal due to interference of a transmission signal from another radar system. Non-Patent Document 1 describes a technique for removing an interference signal included in a beat signal expressed as a complex signal in the frequency domain using an adaptive filter, utilizing the correlation between the positive frequency component and the negative frequency component of the interference signal. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Feng Jin, Siyang Cao “Automotive Radar Interference Mitigation Using Adaptive Noise Canceller”, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 68, NO. 4, APRIL 2019. Summary of the Invention [Problem to be solved by the invention]

[0004] The technology of Non-Patent Document 1 can effectively remove interference components in a frequency range corresponding to a near field, but may not be able to sufficiently remove interference components in a frequency range corresponding to a very near field or a far field. Therefore, there is room for further improvement in removing interference components in a wider frequency range. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to a first aspect of the present disclosure, there is provided a signal processing device (200). The signal processing device includes: a transform unit (210) that performs a Fourier transform on a beat signal (Bw) representing a time domain signal generated by mixing a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that reflects a transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave in a quadrature mixer (105), into a frequency domain first signal (Bwf1) whose frequency components are represented for each frequency bin; and a processing unit (220) that has an adaptive filter (221) including an FIR filter (222) and generates an interference-removed signal (Ts) in which an interference signal component (IFIf) has been removed from the first signal. The processing unit performs adaptive processing that sequentially uses each positive frequency component of the first signal as a primary input signal of the adaptive filter, sequentially uses each negative frequency component of the first signal corresponding to each positive frequency component as a reference input signal of the adaptive filter, and outputs an output signal based on the primary input signal and the reference input signal. In the adaptation processing, the processing unit executes an FIR filter processing for processing the reference input signal using the FIR filter, an output processing for outputting, as the output signal, a residual between the primary input signal and the reference input signal processed by the FIR filter processing, and an update processing for updating tap coefficients of the FIR filter based on the residual, and changes a step size parameter for updating the tap coefficients based on the bin number of a frequency bin of the first signal.

[0007] According to this embodiment, it is more likely that the residual can be reduced in a frequency range corresponding to a long distance, and therefore it is more likely that the interference signal component can be effectively removed from the first signal in the frequency range corresponding to a long distance.

[0008] According to a second aspect of the present disclosure, there is provided a signal processing device (200). The signal processing device includes: a transform unit (210) that performs a Fourier transform on a beat signal (Bw) representing a time domain signal generated by mixing a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that reflects a transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave in a quadrature mixer (105), into a frequency domain first signal (Bwf1) whose frequency components are represented for each frequency bin; and a processing unit (220) that has an adaptive filter (221) including an FIR filter (222) and generates an interference-removed signal (Ts) in which an interference signal component (IFIf) has been removed from the first signal. The processing unit performs adaptive processing that sequentially uses each positive frequency component of the first signal as a primary input signal of the adaptive filter, sequentially uses each negative frequency component of the first signal corresponding to each positive frequency component as a reference input signal of the adaptive filter, and outputs an output signal based on the primary input signal and the reference input signal. In the adaptation processing, the processing unit executes an FIR filter processing for processing the reference input signal using the FIR filter, an output processing for outputting, as the output signal, a residual between the primary input signal and the reference input signal processed by the FIR filter processing, and an update processing for updating tap coefficients of the FIR filter based on the residual, and executes a recalculation processing for executing the FIR filter processing, the output processing, and the update processing using the updated tap coefficients for the current frequency bin of the first signal a predetermined number of times before taking the positive frequency component of the next frequency bin of the first signal as the primary input signal.

[0009] According to this embodiment, the tap coefficients can be updated more frequently than when the recalculation process is not performed, which increases the possibility of effectively removing the interference signal component from the first signal in the frequency range corresponding to the far distance.

[0010] According to a third aspect of the present disclosure, there is provided a signal processing device (200). The signal processing device includes: a transform unit (210) that performs a Fourier transform on a beat signal (Bw) representing a time domain signal generated by mixing a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that reflects a transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave in a quadrature mixer (105), into a frequency domain first signal (Bwf1) whose frequency components are represented for each frequency bin; and a processing unit (220) that has an adaptive filter (221) including an FIR filter (222) and generates an interference-removed signal (Ts) in which an interference signal component (IFIf) has been removed from the first signal. The processing unit performs adaptive processing that sequentially uses each positive frequency component of the first signal as a primary input signal of the adaptive filter, sequentially uses each negative frequency component of the first signal corresponding to each positive frequency component as a reference input signal of the adaptive filter, and outputs an output signal based on the primary input signal and the reference input signal. In the adaptive processing, the processing unit executes: an FIR filter processing for processing the reference input signal using the FIR filter; an output processing for outputting, as the output signal, a residual between the primary input signal and the reference input signal processed by the FIR filter processing; and an update processing for updating tap coefficients of the FIR filter based on the residual. As the adaptive processing, the processing unit executes: a first adaptive processing for inputting, as the primary input signal, positive frequency components of the first signal in order from a frequency bin corresponding to a short distance toward a frequency bin corresponding to a long distance; and a second adaptive processing for inputting, as the primary input signal, positive frequency components of the first signal in order from a frequency bin corresponding to a medium distance toward a frequency bin corresponding to the short distance. The processing unit outputs, as the interference-removed signal, a signal obtained by joining the signal output by the output processing of the first adaptive processing and the signal output by the output processing of the second adaptive processing.

[0011] According to this embodiment, it is possible to suppress the influence of the residual convergence process on the interference-removed signal, and therefore, compared to, for example, simply processing the frequency components of the first signal by adaptive processing in order from frequency bins corresponding to short distances to frequency bins corresponding to long distances, it is more likely that the interference signal components can be effectively removed from the first signal in the frequency range corresponding to very close distances. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a radar device according to a first embodiment. [Figure 2] FIG. 4 is an explanatory diagram showing an example of a high-frequency signal before mixing and a beat signal after mixing. [Figure 3] 4 is a flowchart of interference signal processing in the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing an example of a first signal. [Figure 5] FIG. 10 is a first explanatory diagram showing a state in which a beat signal is multiplied by a window function. [Figure 6] FIG. 10 is a second explanatory diagram showing a state in which a beat signal is multiplied by a window function. [Figure 7] 10 is a flowchart of an adaptation process. [Figure 8] FIG. 1 is an explanatory diagram of an adaptive filter. [Figure 9] An explanatory diagram of an FIR filter. [Figure 10] FIG. 10 is an explanatory diagram showing the relationship between a step size parameter and a bin number. [Figure 11] FIG. 4 is a diagram illustrating joining of output signals. [Figure 12] FIG. 10 is a diagram showing simulation results of adaptive processing. [Figure 13] 10 is a flowchart of interference signal processing in the second embodiment. [Figure 14] FIG. 10 is an explanatory diagram showing an example in which an interference signal occurs at an end of a beat signal. [Figure 15] 10 is a flowchart of interference signal processing in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] A. First embodiment: The radar system 100 shown in FIG. 1 is mounted on a vehicle such as an automobile or a motorcycle, and measures an object OB. The object OB may be, for example, a pedestrian, another vehicle, or an obstacle on the road. "Measuring the object OB" refers to, for example, measuring the distance and angle between the vehicle on which the radar system 100 is mounted and the object OB, and the relative speed of the object OB with respect to the vehicle. The radar system 100 in this embodiment is configured with a millimeter-wave radar that measures the object OB using an FCM (Fast-Chirp Modulation) method.

[0014] As shown in FIG. 1, the radar system 100 includes a signal generating unit 101, a transmitting unit 102, a receiving unit 103, a beat signal generating unit 104 having a quadrature mixer 105, and a signal processing device 200.

[0015] The signal generating unit 101 is configured by, for example, a PLL (Phase Locked Loop) circuit, and generates a transmission signal Tw. In this embodiment, the signal generating unit 101 continuously generates, as the transmission signal Tw, a chirp signal whose frequency is linear with respect to time.

[0016] The transmitting unit 102 is configured as an antenna that radiates a transmission signal Tw into space as an electromagnetic wave Ew, and radiates the transmission signal Tw amplified by a power amplifier PA as the electromagnetic wave Ew. The receiving unit 103 is configured as an antenna that receives the electromagnetic wave Ew reflected by the target object OB as a reception signal Dw. Hereinafter, the electromagnetic wave Ew transmitted by the transmission signal Tw will also be referred to as a transmission wave. Furthermore, the electromagnetic wave Ew reflected by the target object OB will also be referred to as a reflected wave.

[0017] The beat signal generating unit 104 generates a beat signal Bw. The beat signal Bw represents a time-domain complex signal generated by mixing the received signal Dw and the transmitted signal Tw in the quadrature mixer 105. In addition to the quadrature mixer 105, the beat signal generating unit 104 has a filter unit 106 configured by a low-pass filter, and an analog-to-digital converter 107 configured by an analog-to-digital converter (ADC).

[0018] In this embodiment, the beat signal generation unit 104 generates signals BwI and BwQ. The signal BwI is a signal based on a signal obtained by mixing a local oscillation signal LO, which is in phase with the transmission signal Tw, with a reception signal Dw amplified by a low-noise amplifier LNA. The signal BwQ is a signal based on a signal obtained by mixing a local oscillation signal LO, which is delayed in phase by 90° relative to the transmission signal Tw, with a reception signal Dw amplified in the same manner. The filter unit 106 attenuates high-frequency components from the output signal of the quadrature mixer 105 to suppress aliasing in the analog-to-digital conversion unit 107. The analog-to-digital conversion unit 107 converts the signal processed by the filter unit 106 into a time-domain digital signal and outputs it. In this way, the signal BwI output by the beat signal generation unit 104 corresponds to the real part of the beat signal Bw, and the signal BwQ corresponds to the imaginary part of the beat signal Bw.

[0019] FIG. 2 is a schematic graph with time on the horizontal axis and frequency on the vertical axis. FIG. 2 shows an example of a beat signal Bw, as well as examples of a local oscillation signal LO and a received signal Dw used to generate the beat signal Bw. In FIG. 2, the received signal Dw is schematically represented by a desired signal Dwp and an interference signal Iw. The interference signal Iw is generated when electromagnetic waves transmitted from a radar system or the like mounted on another vehicle interfere with the received signal Dw. Also, in FIG. 2, the beat signal Bw is schematically represented by a desired signal IFO derived from a target object OB and an interference signal IFI derived from the interference signal Iw. As shown in FIG. 2, the desired signal IFO is a signal having only positive frequencies. More specifically, the desired signal IFO has only a specific positive frequency corresponding to the target object OB. In contrast, the interference signal IFI is a signal having both positive and negative frequencies. The interference signal IFI is symmetrical with respect to the time Tc at which the local oscillation signal LO and the interference signal Iw intersect, and the time waveform of the interference signal IFI in the positive frequency range is approximately symmetrical with the time waveform of the interference signal IFI in the negative frequency range.

[0020] The signal processing device 200 is configured as a computer including a CPU, a storage unit, and an input / output interface for inputting and outputting signals from and to the outside.

[0021] The signal processing device 200 includes a conversion unit 210, a processing unit 220, and a measurement unit 230. In this embodiment, the conversion unit 210, the processing unit 220, and the measurement unit 230 are functional units that are realized by a CPU executing a program stored in a storage unit of the signal processing device 200. In other embodiments, the conversion unit 210, the processing unit 220, and the measurement unit 230 may be configured as devices separate from the signal processing device 200 that operate in response to instructions from the CPU, for example. Furthermore, some or all of the functions of the signal processing device 200 may be realized by, for example, a hardware circuit.

[0022] The converter 210 performs a Fourier transform on the beat signal Bw, which is the above-described complex time waveform, to generate a first signal Bwf1. More specifically, the converter 210 performs a fast Fourier transform on the beat signal Bw to generate the first signal Bwf1. The first signal Bwf1 refers to a frequency domain signal in which the frequency components of the beat signal Bw are represented for each frequency bin. In this embodiment, the number of frequency bins of the beat signal Bw is 1024.

[0023] The processing unit 220 generates an interference-removed signal Ts from the first signal Bwf1 by removing the interference signal component IFIf contained in the first signal Bwf1. The processing unit 220 has an adaptive filter 221 including an FIR (Finite Impulse Response) filter 222. Details of the adaptive filter 221 and the FIR filter 222 will be described later.

[0024] As will be described later, the measurement unit 230 measures the target OB based on the generated post-interference-removal signal Ts.

[0025] The signal processing device 200 in this embodiment generates the above-described interference-removed signal Ts by executing the interference signal processing shown in Fig. 3. In this embodiment, the interference signal processing is executed every time a beat signal Bw is input to the signal processing device 200. More specifically, in this embodiment, the transmitter 102 transmits a series of multiple transmission signals Tw as a set of chirp signals, and multiple beat signals Bw are generated corresponding to these transmission signals Tw and input to the signal processing device 200. The chirp signal set is usually composed of a number of chirp signals that is a power of 2, for example, 512 chirp signals.

[0026] In step S110, the converter 210 performs a Fourier transform on the beat signal Bw to generate a first signal Bwf1. In step S110, the converter 210 multiplies the beat signal Bw by a window function (for example, a Hanning window, a Hamming window, or a Blackman window), and then performs a fast Fourier transform on the signal multiplied by the window function to generate the first signal Bwf1.

[0027] FIG. 4 is a schematic graph with frequency on the horizontal axis and amplitude on the vertical axis. FIG. 4 shows an example of the first signal Bwf1. FIG. 4 shows a signal derived from the beat signal Bw described in FIG. 2 as an example of the first signal Bwf1. In FIG. 4, the first signal Bwf1 is represented by a desired signal component IFOf derived from the target OB and an interference signal component IFIf. As shown in FIG. 4, the first signal Bwf1 includes positive frequency components representing frequency components at positive frequencies and negative frequency components representing frequency components at negative frequencies. To facilitate understanding of the technology, FIG. 4 shows only amplitude as the frequency component of the first signal Bwf1. However, since the first signal Bwf1 is a complex signal, in reality, the frequency components have phase in addition to amplitude.

[0028] The number of the frequency bin in the first signal Bwf1 is also referred to as the bin number n. In the first signal Bwf1, the same bin number n is assigned to positive frequency bins and negative frequency bins that correspond to each other. These "corresponding frequency bins" refer to positive frequency bins and negative frequency bins that have the same absolute frequency values. FIG. 4 schematically illustrates the bin number n. As shown in FIG. 4, the positive frequency bins and negative frequency bins are assigned consecutive numbers that increase by one in order from the frequency bin with the smallest absolute frequency value to the frequency bin with the largest absolute frequency value. Hereinafter, positive frequency components and negative frequency components that have "corresponding frequency bins" are also simply referred to as "positive frequency components corresponding to negative frequency components" and "negative frequency components corresponding to positive frequency components."

[0029] As described above, the positive and negative frequency ranges of the interference signal IFI included in the beat signal Bw, which is a complex time waveform, are approximately symmetrical and correlated, and therefore the positive and negative frequency components of the interference signal component IFIf included in the first signal Bwf1 obtained by Fourier transforming the beat signal Bw are also correlated. More specifically, the positive and negative frequency components of the interference signal component IFIf are approximately symmetrical with respect to the zero frequency position. Note that, although not shown in FIG. 4 , the difference between the corresponding positive and negative frequency components of the interference signal component IFIf actually becomes larger in higher frequency ranges. Therefore, while the positive and negative frequency components of the interference signal component IFIf are approximately symmetrical with respect to the zero frequency position as a whole, this symmetry becomes somewhat weaker in higher frequency ranges.

[0030] 5 and 6 are schematic graphs with time on the horizontal axis and amplitude on the vertical axis. FIG. 5 shows a state in which the beat signal Bw is multiplied by a Hanning window when an interference signal IFI occurs earlier than time Tc of the beat signal Bw. FIG. 6 shows a state in which the beat signal Bw is multiplied by a Hanning window when an interference signal IFI occurs at time Tc. As shown in FIGS. 5 and 6, multiplication of the beat signal Bw by the window function reduces the signal strength of the beat signal Bw closer to the end of the time position of the beat signal Bw. More specifically, FIG. 5 shows a state in which the strength of the earlier side of the interference signal IFI contained in the beat signal Bw is reduced more than the strength of the later side due to multiplication by the window function. That is, in FIG. 5, the strength of the positive frequency range of the interference signal IFI is lower than the strength of the negative frequency range. 5, for example, when the interference signal IFI occurs later than the time Tc of the beat signal Bw, the intensity of the negative frequency range of the interference signal IFI is reduced more than the intensity of the positive frequency range by multiplying the beat signal Bw by a window function such as a Hanning window. Therefore, when the interference signal IFI occurs earlier or later than the time Tc of the beat signal Bw, the difference between the positive frequency component and the negative frequency component in the higher frequency range of the interference signal component IFIf in the first signal Bwf1 generated from this beat signal Bw becomes larger.

[0031] 3, the processing unit 220 determines whether the intensity of the interference signal component IFIf of the first signal Bwf1 is equal to or greater than a predetermined intensity. In this embodiment, the processing unit 220 determines whether the integrated value of the power in the negative frequency range of the first signal Bwf1 is equal to or greater than a predetermined reference power value in step S120. Note that in other embodiments, the processing unit 220 may determine whether the integrated value of the amplitude in the negative frequency range of the first signal Bwf1 is equal to or greater than a predetermined reference amplitude in step S120, for example.

[0032] If it is determined in step S120 that the integrated power value is equal to or greater than the reference power value, that is, if it is determined that the intensity of the interference signal component IFIf is equal to or greater than a predetermined intensity, then in step S130, the processing unit 220 executes adaptive processing. The adaptive processing refers to processing in which each positive frequency component of the first signal Bwf1 is used in turn as a primary input signal of the adaptive filter 221, and each negative frequency component corresponding to each positive frequency component is used in turn as a reference input signal of the adaptive filter 221, and an output signal based on the primary input signal and the reference input signal is output. The primary input signal of the adaptive filter 221 is also called an observed signal, a primary signal, or a primary input, and is input to a P terminal of the adaptive filter 221. The reference input signal of the adaptive filter 221 is also called a reference signal or a reference input, and is input to an N terminal of the adaptive filter 221. Examples of the adaptive algorithm used in the adaptive processing include the least mean square (LMS) algorithm, the normalized least mean square (NLMS) algorithm, and the recursive least square (RLS) algorithm.

[0033] As shown in FIG. 3 , in this embodiment, the processing unit 220 performs a first adaptive process and a second adaptive process as adaptive processes. The first adaptive process and the second adaptive process have different orders of processing frequency bins. More specifically, in the first adaptive process, the processing unit 220 sequentially sets positive frequency components as the primary input signals of the adaptive filter 221, from frequency bins corresponding to short distances to frequency bins corresponding to long distances. In the second adaptive process, the processing unit 220 sequentially sets negative frequency components as the primary input signals of the adaptive filter 221, from frequency bins corresponding to medium distances to frequency bins corresponding to short distances. The medium distance refers to a distance farther than the short distance and closer than the long distance. The long distance refers to a distance farther than the short and medium distances. A frequency bin with a smaller bin number n corresponds to a closer distance, and a frequency bin with a larger bin number n corresponds to a farther distance. Hereinafter, when there is no particular distinction between the first adaptive process and the second adaptive process, both processes will be simply referred to as adaptive processes.

[0034] In this embodiment, in the first adaptation process, the processing unit 220 processes positive frequency components in order from the frequency bin corresponding to the closest distance to the frequency bin corresponding to the farthest distance. That is, for example, if the number of frequency bins is 1024, in the first adaptation process, the processing unit 220 processes positive frequency components in order from the frequency bin with bin number 1 to the frequency bin with bin number 1024.

[0035] In the adaptive processing, the processing unit 220 executes the steps shown in Fig. 7. In this embodiment, the processing unit 220 repeatedly executes steps S131 to S135 shown in Fig. 10 for one frequency bin a plurality of times.

[0036] 7, in the adaptive processing, first, in step S131, the processing unit 220 executes FIR filter processing. This refers to processing of the reference input signal of the adaptive filter 221.

[0037] 8, a negative frequency component N(n) of bin number n is input to the FIR filter 222, and an output component y(n) is output. The output component y(n) can also be said to be a reference input signal processed by FIR filtering. The output component y(n) is expressed by the following equation (1). y(n)=w(n) T X …(1) In the above equation (1), X represents an input vector. w(n) represents a tap coefficient of the FIR filter 222. The subscript T represents the transpose of a vector. The tap coefficient w(n) is also called an FIR filter coefficient.

[0038] As shown in Fig. 9, the FIR filter 222 is configured as a direct filter with L taps. The input vector X is an L-th order vector having negative frequency components N(n) to N(n-(L-1)) as components. The tap coefficient w(n) has components w1(n) to w L 9, the FIR filter 222 convolves the input vector X with the tap coefficient w(n). As a result, the sum of the products of the components of the input vector X and the components of the tap coefficient w(n) at each tap of the FIR filter 222 is output as the output component y(n) of the FIR filter 222. In other embodiments, the FIR filter 222 may be configured as a transposed, cascaded, or lattice filter.

[0039] Next, in step S132 of FIG. 7, the processing unit 220 executes output processing. The output processing refers to processing for outputting, as the output signal of the adaptive filter 221 shown in FIG. 8, a residual ε(n) between the primary input signal of the adaptive filter 221 and a reference input signal processed by FIR filter processing. That is, in the output processing, the residual ε(n) between the positive frequency component P(n) in the frequency bin with bin number n and the output component y(n) is output as the residual ε(n). Hereinafter, the residual ε(n) will also be referred to as the output signal ε(n). The output signal ε(n) is generated by the subtractor 223 as shown in FIG. 8. The output signal (n) is expressed by the following equation (2). ε(n)=P(n)-y(n) …(2)

[0040] Next, in step S133 of Fig. 7, the processing unit 220 executes an update process. The update process refers to a process of updating the tap coefficient w(n) based on the residual ε(n) using the above-mentioned adaptive algorithm. The tap coefficient w(n) is updated using the following equation (3). w R (n)=w(n)+με(n)X * …(3) In the above formula (3), w R represents the tap coefficient after updating. μ represents the step size parameter for updating the tap coefficient w(n). X * represents the complex conjugate of the input vector X.

[0041] In this embodiment, the processing unit 220 changes the step-size parameter μ based on the bin number n. More specifically, the processing unit 220 increases the step-size parameter μ overall with respect to the bin number n. More specifically, in this embodiment, the processing unit 220 monotonically increases the step-size parameter μ with respect to the bin number n. As shown in FIG. 10 , the step-size parameter μ in this embodiment is defined as a linear function having a positive slope with respect to the bin number n. Note that, in this specification, monotonically increasing refers to a variable increasing without decreasing relative to another variable. Therefore, in other embodiments, when the step-size parameter μ is monotonically increasing with respect to the bin number n, the step-size parameter μ may be defined as, for example, a quadratic function or an exponential function that monotonically increases with respect to the bin number n, or as a function having a step-like portion that assumes a constant value with respect to the bin number n.

[0042] As described above, the difference between the positive and negative frequency components of the interference signal component IFIf becomes larger in a higher frequency range. Therefore, for example, if the step-size parameter μ is constant regardless of the bin number n, even if the tap coefficient w(n) can be appropriately updated in a lower frequency range, the update width of the tap coefficient w(n) may be insufficient in a higher frequency range, and the tap coefficient w(n) may not be appropriately updated. As a result, even if the residual error ε(n) is relatively small in a lower frequency range, the residual error ε(n) may become large in a higher frequency range. In this embodiment, the step-size parameter μ is changed based on the bin number n as described above, thereby increasing the possibility of appropriately updating the tap coefficient w(n) even in a higher frequency range, i.e., in a frequency range corresponding to a more distant region. Therefore, the residual error ε(n) may be reduced in a frequency range corresponding to a more distant region.

[0043] Next, in step S134 of Fig. 7, the processing unit 220 determines whether the number of recalculations is equal to or greater than a predetermined number. The number of recalculations refers to the number of times a recalculation process, which will be described later, has been executed. The number of recalculations is counted for each frequency bin. When step S134 is executed for the first time for a certain frequency bin, the number of recalculations is 0. In this embodiment, in step S134, the processing unit 220 determines whether the number of recalculations is equal to or greater than two.

[0044] If it is determined in step S134 that the number of recalculations is less than two, the processing unit 220 returns the process to step S131. In steps S131 to S133 that are executed again, the processing unit 220 executes the FIR filter process, the output process, and the update process again using the tap coefficients that were updated immediately before.

[0045] For example, in step S131, which is executed for the second time for a certain frequency bin, the processing unit 220 uses the tap coefficient w(n) updated in step S133, which was executed for the first time, as the tap coefficient w(n) in the above equation (1). RSimilarly, in step S132, which is executed for the second time, the processing unit 220 uses the updated tap coefficient w as the output component y(n) in the above equation (2). R Similarly, in step S133, which is executed for the second time, the processing unit 220 uses the updated tap coefficient w(n) as the tap coefficient w(n) in the above equation (3) to output the output signal ε(n). R (n) is used to further update the tap coefficients.

[0046] As described above, in this embodiment, before processing the frequency components of the next frequency bin of the first signal Bwf1 by adaptive processing, more specifically, before using the positive frequency components of the next frequency bin as the main input signal of the adaptive filter 221, the processing unit 220 performs a recalculation process, which is a process of performing FIR filter processing, update processing, and output processing again on the current frequency bin using the updated tap coefficients. Note that when the bin number of the current frequency bin in the first adaptive processing is n, the "next frequency bin" is the (n+1)th frequency bin. When the bin number of the current frequency bin in the second adaptive processing is n, the "next frequency bin" is the (n-1)th frequency bin.

[0047] If it is determined in step S134 that the number of recalculations is two or more, the processing unit 220 proceeds to step S135. That is, in this embodiment, the processing unit 220 executes the recalculation process a predetermined number of times, more specifically, twice. In this embodiment, it can also be said that steps S131 to S133 are executed a total of three times for a certain frequency bin. In other embodiments, the number of recalculations may be, for example, one time or three or more times. However, it is preferable that the number of recalculations is one to three times.

[0048] Unlike the present embodiment, for example, when processing a time-domain signal in real time using an adaptive filter, it is generally difficult to perform processing similar to the above-described recalculation process, i.e., to perform processing using an FIR filter or the like multiple times on one time component, due to time constraints. In contrast, in the present embodiment, the adaptive processing processes the first signal Bwf1, which is a frequency-domain signal, and therefore the recalculation process can be easily performed.

[0049] In step S135, the processing unit 220 determines whether the current frequency bin is the last frequency bin in the adaptive process. If the processing unit 220 determines that the current frequency bin is not the last frequency bin, the processing unit returns to step S131. Thereafter, steps S131 to S134 are similarly executed for the next frequency bin. If the processing unit 220 determines in step S135 that the current frequency bin is the last frequency bin, the adaptive process ends.

[0050] In step S140 of FIG. 3, the processing unit 220 joins the output signal of the first adaptive processing and the output signal of the second adaptive processing, and outputs the joined signal to the measurement unit 230 as the interference-removed signal Ts.

[0051] The upper part of Fig. 11 shows signal Op1 as an example of an output signal of the first adaptive processing, and signal Op2 as an example of an output signal of the second adaptive processing. The upper part of Fig. 11 also shows signal Bwf1a as an example of the first signal Bwf1 processed by the first adaptive processing and the second adaptive processing. The lower part of Fig. 11 shows signal Oj in which signals Op1 and Op2 are spliced together. Fig. 11 also shows frequency bin St1 processed first in the first adaptive processing, frequency bin St2 processed first in the second adaptive processing, and frequency bin E in which signals Op1 and Op2 are spliced together. Note that in Fig. 11, signals Op1, Op2, Bwf1a, and Oj are all represented by only interference signal components IFIf, but in reality, at least one of signals Op1 and Op2, as well as signals Bwf1a and Oj, contain signals derived from target OB. The bin number of frequency bin E is greater than the bin number of frequency bin St1 and less than the bin number of frequency bin St2. More specifically, in the example of FIG. 11 , the frequency position corresponding to the bin number of frequency bin E corresponds to the minimum point of signal Op2, and corresponds to the point where the convergence process described below ends. Signal Oj is generated as a signal having frequency components similar to signal Op2 in a frequency range equal to or less than the bin number of frequency bin E, and having frequency components similar to signal Op1 in a frequency range greater than the bin number of frequency bin E.

[0052] Generally, it takes a certain amount of time for the residual to converge in adaptive processing. When processing frequency-domain discrete signals, as in the adaptive processing of this embodiment, "a certain amount of time" refers to "a certain number of frequency bins." For example, in the example of FIG. 11 , there are regions where the residual ε(n) is relatively high in the frequency region around frequency bin St1 of signal Op1 and the frequency region around frequency bin St2 of signal Op2. These regions correspond to the convergence process until the residual ε(n) converges. In this embodiment, signals Op1 and Op2 are spliced together to generate signal Oj, and this signal Oj is output as interference-canceled signal Ts. Therefore, compared to, for example, when a signal consisting of a single output signal is output as interference-canceled signal Ts, the influence of this convergence process on interference-canceled signal Ts can be suppressed. For example, if, instead of the second adaptive processing, adaptive processing is performed in which positive frequency components are used as the main input signals to adaptive filter 221 in order from the frequency bin corresponding to the long distance toward the frequency bin corresponding to the short distance, as described above, the difference between the positive and negative frequency components is large in the higher frequency range, and therefore the residual ε(n) may diverge rather than converge. In the second adaptive processing of this embodiment, negative frequency components are processed starting from the frequency bin corresponding to the medium distance, and therefore such divergence of the residual ε(n) can be suppressed.

[0053] FIG. 12 is a graph in which the horizontal axis represents frequency bins and the vertical axis represents power. In FIG. 12, frequency bin numbers of negative frequency components are assigned negative signs. FIG. 12 shows simulation results when a signal Bwf1b, which is obtained by Fourier transforming a beat signal Bw including an interference signal IFI at the time Tc described above, is processed by adaptive processing. FIG. 12 also shows simulation results for a signal Tsa generated by processing the signal Bwf1b by the adaptive processing described above as the interference-removed signal Ts. FIG. 12 also shows simulation results for a signal Tsb generated by processing a similar signal Bwf1a by a different adaptive processing from the adaptive processing described above. This different adaptive processing is an adaptive processing in which each frequency component of the signal Bwf1a is processed in order from frequency bin number 1 to frequency bin number 1024, with a constant step-size parameter μ and without performing recalculation processing. The signal Bw1fb includes a desired signal component IFOf derived from the target OB and an interference signal component IFIf, similar to the first signal Bwf1 described in Fig. 4. In the example of Fig. 12, the desired signal component IFOf is included near the position of the frequency bin with bin number n of 180. The interference signal component IFIf of the signal Bwf1b is included across the entire frequency range.

[0054] As shown in FIG. 12, when signal Bwf1b is subjected to interference signal processing, the interference signal component IFIf is reduced, and therefore the S / N ratio of the desired signal component IFOf to the interference signal component IFIf in signal Tsa increases compared to the S / N ratio in signal Bw1fa. Also, as shown in FIG. 12, it can be seen that the interference signal component IFIf is particularly effectively removed in signal Tsa compared to signal Tsb in the frequency range corresponding to the very close range and the frequency range corresponding to the far range. More specifically, it can be seen that the interference signal component IFIf is effectively reduced in signal Tsa compared to signal Tsb at frequency positions with bin numbers 1 to 20 and at frequency positions with bin numbers 600 or greater. In this embodiment, the frequency positions with bin numbers 1 to 20 correspond to frequency positions at distances of approximately 0 m to 6 m from the receiving unit 103, and the frequency positions with bin numbers 600 or greater correspond to frequency positions at distances of approximately 180 m or greater from the receiving unit 103.

[0055] After step S140, the processing unit 220 terminates the interference signal processing. The processing unit 220 also terminates the interference signal processing if it is determined in step S120 that the intensity of the interference signal component IFIf is less than a predetermined intensity. In this case, the first signal Bwf1 is output to the measurement unit 230. If it is determined that the intensity of the interference signal component IFIf is less than a predetermined intensity, the intensity of the interference signal component IFIf in the first signal Bwf1 is relatively small compared to the desired signal component IFOf. Therefore, in this case, even if the first signal Bwf1 is used to measure the target OB, the influence of the interference signal component IFIf on the measurement result of the target OB is suppressed.

[0056] The measurement unit 230 measures the target OB based on the interference-removed signals Ts generated by the above-described interference signal processing. In this embodiment, the measurement unit 230 measures the target OB based on all of the interference-removed signals Ts generated by processing the beat signals Bw based on each signal constituting the above-described chirp signal group by interference signal processing, and all of the first signals Bwf1 for which the intensity of the interference signal component IFIf is determined to be less than a predetermined intensity. In this case, the measurement unit 230 may measure the target OB by, for example, individually analyzing these signals, or may measure the target OB based on the results of further Fourier transforming these signals.

[0057] According to the signal processing device 200 of the present embodiment described above, the processing unit 220 sequentially sets each positive frequency component of the first signal Bwf1 as a primary input signal to the adaptive filter 221, sequentially sets each negative frequency component corresponding to each positive frequency component as a reference input signal to the adaptive filter 221, and outputs an output signal based on the primary input signal. In this adaptive processing, the processing unit 220 performs the following steps: FIR filter processing to process the reference input signal using the FIR filter 222; output processing to output, as the output signal of the adaptive filter 221, a residual ε(n) between the primary input signal of the adaptive filter 221 and the reference input signal processed by the FIR filter 222; and update processing to update the tap coefficient w(n) based on the residual ε(n). The processing unit 220 then varies the step-size parameter μ for updating the tap coefficient w(n) based on the bin number n. This increases the likelihood of reducing the residual ε(n) in the frequency range corresponding to the far region. This increases the likelihood of effectively removing the interference signal component IFIf from the first signal Bwf1 in the frequency range corresponding to the far region.

[0058] Furthermore, in this embodiment, the processing unit 220 monotonically increases the step-size parameter μ with respect to the bin number n. This allows the step-size parameter μ to be increased in response to the fact that the difference between the positive and negative frequency components of the interference signal component IFIf becomes larger in a higher frequency range. This increases the likelihood that the tap coefficient w(n) can be updated more appropriately, thereby increasing the likelihood that the interference signal component IFIf can be effectively removed from the first signal Bwf1 in a frequency range corresponding to the far field.

[0059] In this embodiment, the processing unit 220 also updates the updated tap coefficient w before the positive frequency component of the next frequency bin is used as the main input signal of the adaptive filter 221. R Using the tap coefficient w(n), a recalculation process is performed a predetermined number of times to perform FIR filtering, output processing, and update processing for the current frequency bin. This increases the number of times the tap coefficient w(n) is updated compared to when the recalculation process is not performed. This increases the likelihood that the interference signal component IFIf can be effectively removed from the first signal Bwf1 in the frequency range corresponding to the far field.

[0060] Furthermore, in this embodiment, the processing unit 220 performs two adaptive processes: a first adaptive process in which positive frequency components are used as the primary input signal of the adaptive filter 221 in order from the frequency bin corresponding to the short distance to the frequency bin corresponding to the long distance; and a second adaptive process in which positive frequency components are used as the primary input signal of the adaptive filter 221 in order from the frequency bin corresponding to the intermediate distance to the frequency bin corresponding to the short distance. The processing unit 220 outputs a signal Oj obtained by splicing together a signal Op1 output by the output process of the first adaptive process and a signal Op2 output by the output process of the second adaptive process as the interference-canceled signal Ts. This makes it possible to prevent the interference-canceled signal Ts from being affected by the convergence process of the residual ε(n). Therefore, for example, compared to simply processing the frequency components of the first signal in order from the frequency bin corresponding to the short distance to the frequency bin corresponding to the long distance by adaptive processing, the interference signal component IFIf can be effectively removed from the first signal Bwf1 in the frequency range corresponding to the very near region.

[0061] B. Second embodiment: The signal processing device 200 in the second embodiment executes the interference signal processing shown in Fig. 13. In Fig. 13, the same steps as those in Fig. 3 described in the first embodiment are denoted by the same reference numerals as in Fig. 3. Unlike the first embodiment, the signal processing device 200 in this embodiment executes a determination process, which will be described later, before executing an adaptive process in the interference signal processing. The configurations of the radar system 100 and the signal processing device 200 in the second embodiment that are not particularly described are the same as those in the first embodiment.

[0062] The determination process refers to a process of determining whether the difference in signal intensity between the positive frequency components in the high-frequency range of the second signal Bwf2 shown in the lower part of FIG. 14 and the negative frequency components in the high-frequency range is equal to or less than a predetermined reference value. The second signal Bwf2 is generated by Fourier transforming the beat signal Bw into a frequency domain signal in which the frequency components are represented for each frequency bin. In this specification, the "high-frequency range" refers to a frequency range in which the absolute value of the frequency is higher than a predetermined frequency.

[0063] 13, the conversion unit 210 Fourier transforms the beat signal Bw into a second signal Bwf2. In step S102, the conversion unit 210 Fourier transforms the beat signal Bw into the second signal Bwf2 without changing the symmetry of the interference signal IFI in the beat signal Bw, which is derived from the mixing signal Iw. More specifically, in step S102, the conversion unit 210 Fourier transforms the beat signal Bw directly without multiplying the beat signal Bw by a window function.

[0064] In step S104, processing unit 220 executes a determination process. In this embodiment, in step S104, processing unit 220 determines whether the difference between the integrated value of the power of positive frequency components in the high frequency range and the integrated value of the power of negative frequency components in the corresponding frequency range is 10% or less of the integrated value of the power of the positive frequency components. If processing unit 220 determines in step S104 that the difference in the integrated values of power is 10% or less, that is, if processing unit 220 determines that the signal strength difference is equal to or less than the reference value, processing unit 220 executes step S110 and subsequent steps in the same manner as described in FIG. 3.

[0065] If it is determined in step S104 that the difference in the integrated power values exceeds 10%, that is, if it is determined that the signal intensity difference is greater than the reference value, then in step S142, the processing unit 220 performs a Fourier transform on the beat signal Bw to convert it into a first signal Bwf1. Thereafter, the processing unit 220 terminates the interference signal processing. In this case, the first signal Bwf1 is output to the measurement unit 230. Note that in this embodiment, the beat signal Bw converted into the first signal Bwf1 in steps S110 and S142 is the same signal as the beat signal Bw converted into the second signal Bwf2 in step S102.

[0066] The upper part of Fig. 14 shows a schematic graph with the horizontal axis representing time and the vertical axis representing amplitude, while the lower part of Fig. 14 shows a schematic graph with the horizontal axis representing frequency and the vertical axis representing amplitude. The upper part of Fig. 14 shows an example in which an interference signal IFI occurs at the left end of the time position of the beat signal Bw, i.e., at the earlier end of the beat signal Bw. The lower part of Fig. 14 shows an example of a second signal Bwf2 generated by Fourier transforming this beat signal Bw. In Fig. 14, the second signal Bwf2 is represented by a desired signal component IFOf and an interference signal component IFIf, similar to the first signal Bwf1 described in Fig. 4.

[0067] As shown in FIG. 14, when an interference signal IFI occurs at the end of the beat signal Bw, all or part of the interference signal IFI may be missing. More specifically, in the example of FIG. 14, a portion of the signal in the positive frequency range of the interference signal IFI is missing, as shown in the upper part of FIG. 14. This also results in a portion of the positive frequency component of the interference signal component IFIf included in the second signal Bwf2 being missing, as shown in the lower part of FIG. 14. Thus, when the interference signal IFI occurs at the end of the beat signal Bw, the symmetry between the positive and negative frequency components of the interference signal component IFIf included in the first signal Bwf1 and the second signal Bwf2 is reduced. Therefore, in this case, when adaptive processing is performed on the first signal Bwf1, the residual ε(n) may diverge and not converge. In this embodiment, the above-described determination processing can determine the symmetry between the positive and negative frequency components based on the signal intensity difference between the positive and negative frequency components. If the signal strength difference is determined to be equal to or less than the reference value, that is, if there is a high degree of symmetry between the positive and negative frequency components, adaptive processing is performed, but if the opposite is true, adaptive processing is not performed, thereby suppressing divergence of the residual error ε(n) in the adaptive processing. It is preferable that the range of the high frequency range and the magnitude of the reference value described above be determined so that the symmetry between the positive and negative frequency components can be appropriately determined.

[0068] Although not shown, the same situation occurs when an interference signal IFI occurs at the right end of the beat signal Bw, i.e., at the slower end of the beat signal Bw. In this case, the negative frequency band of the interference signal IFI is partially or entirely lost, resulting in the negative frequency components of the interference signal component IFIf included in the first signal Bwf1 and the second signal Bwf2 being partially or entirely lost.

[0069] As described above, multiplying the beat signal Bw by a window function reduces the signal strength near the ends of the beat signal Bw. Therefore, when an interference signal IFI occurs at the end of the beat signal Bw, multiplying the beat signal Bw by a window function such as a Hanning window can further reduce the amplitude of the interference signal IFI compared to when the interference signal IFI occurs at time Tc of the beat signal Bw. Then, by performing a Fourier transform on the beat signal Bw multiplied by this window function to generate a first signal Bwf1, the signal strength of the interference signal component IFIf in the first signal Bwf1 can be reduced. In other words, when an interference signal IFI occurs at the end of the beat signal Bw, performing step S142 described above can effectively reduce the signal strength of the interference signal component IFIf in the first signal Bwf1. Therefore, in this case, even if the first signal Bwf1 generated in step S142 is used to measure the target OB, the influence of the interference signal component IFIf on the measurement results of the target OB is suppressed.

[0070] According to the second embodiment described above, the processing unit 220 executes a determination process to determine whether the signal strength difference between the positive frequency component and the negative frequency component in the high-frequency decay period of the second signal Bwf2 is equal to or less than a reference value, and executes an adaptive process if the signal strength difference is equal to or less than the reference value, thereby suppressing the divergence of the residual ε(n) in the adaptive process.

[0071] C. Third embodiment: The signal processing device 200 in the third embodiment executes the interference signal processing of Fig. 15. In Fig. 15, the same steps as those in Fig. 13 described in the second embodiment are denoted by the same reference numerals as in Fig. 13. The signal processing device 200 in this embodiment executes the determination process in the same manner as in the second embodiment. However, unlike the second embodiment, in this embodiment, the signal processing device 200 compares the most frequent value of the power of the positive frequency components in the high frequency range of the second signal Bwf2 with the most frequent value of the power of the negative frequency components in the high frequency range of the second signal Bwf2 in the determination process. The configurations of the radar system 100 and the signal processing device 200 in the third embodiment that are not particularly described are the same as those in the second embodiment.

[0072] In step S104b of Fig. 15, the processing unit 220 executes a determination process. In this embodiment, in step S104b, the processing unit 220 determines whether the difference in the mode of power in the above-mentioned high frequency range is 10% or less with respect to the mode of power of the positive frequency component. If the processing unit 220 determines in step S104b that the difference in the mode of power is 10% or less, that is, if the processing unit 220 determines that the signal strength difference is less than or equal to the reference value, it executes step S110 and subsequent steps in the same manner as described in Fig. 13. If the processing unit 220 determines that the signal strength difference is greater than the reference value, it executes step S142 in the same manner as described in Fig. 13.

[0073] The third embodiment described above can also suppress divergence of the residual ε(n) in the adaptive processing, similarly to the second embodiment. Note that in the second and third embodiments, the integrated value or mode value of the power of each component is compared in the determination processing, but when performing the determination processing in other embodiments, for example, the integrated value or mode value of the amplitude of each component may be compared.

[0074] D. Other Embodiments: (D-1) In the above embodiment, the processing unit 220 performs all of the following: (a) changing the step-size parameter μ based on the bin number n in the adaptive process, (b) performing the recalculation process a predetermined number of times in the adaptive process, and (c) performing the first adaptive process and the second adaptive process as the adaptive process. However, the processing unit 220 may perform only one or only two of the above (a) to (c).

[0075] (D-2) In the above embodiment, the processing unit 220 monotonically increases the step-size parameter μ with respect to the bin number n in the adaptive processing. However, the processing unit 220 does not have to monotonically increase the step-size parameter μ with respect to the bin number n in the adaptive processing. In this case, the step-size parameter μ may be defined as a function that has a portion that decreases with respect to the bin number n and that increases overall with respect to the bin number n, for example.

[0076] (D-3) In the above embodiment, the processing unit 220 determines whether the intensity of the interference signal component IFIf of the first signal Bwf1 is equal to or greater than a predetermined intensity in step S120 of Figures 3, 13, and 15, but this determination does not have to be performed.

[0077] E. Other forms: The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments can be appropriately replaced or combined to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0078] <Feature 1> A signal processing device (200) includes: a transform unit (210) that Fourier transforms a beat signal (Bw) representing a time domain signal generated by mixing a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that reflects a transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave in a quadrature mixer (105) into a first signal (Bwf1) in the frequency domain, whose frequency components are represented for each frequency bin; and a processing unit (220) that has an adaptive filter (221) including an FIR filter (222) and generates an interference-removed signal (Ts) in which an interference signal component (IFIf) has been removed from the first signal. The processing unit performs adaptive processing that sequentially uses each positive frequency component of the first signal as a primary input signal of the adaptive filter, sequentially uses each negative frequency component of the first signal corresponding to each positive frequency component as a reference input signal of the adaptive filter, and outputs an output signal based on the primary input signal and the reference input signal. In the adaptation processing, the processing unit executes an FIR filter processing for processing the reference input signal using the FIR filter, an output processing for outputting, as the output signal, a residual between the primary input signal and the reference input signal processed by the FIR filter processing, and an update processing for updating tap coefficients of the FIR filter based on the residual, and changes a step size parameter for updating the tap coefficients based on the bin number of a frequency bin of the first signal.

[0079] <Mode 2> In the signal processing device of mode 1, the processing unit may monotonically increase the step size parameter with respect to the bin number.

[0080] <Feature 3> A signal processing device (200) includes: a transform unit (210) that Fourier transforms a beat signal (Bw) representing a time domain signal generated by mixing a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that reflects a transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave in a quadrature mixer (105) into a first signal (Bwf1) in the frequency domain, whose frequency components are represented for each frequency bin; and a processing unit (220) that has an adaptive filter (221) including an FIR filter (222) and generates an interference-removed signal (Ts) in which an interference signal component (IFIf) is removed from the first signal. The processing unit performs adaptive processing that sequentially uses each positive frequency component of the first signal as a primary input signal of the adaptive filter, sequentially uses each negative frequency component of the first signal corresponding to each positive frequency component as a reference input signal of the adaptive filter, and outputs an output signal based on the primary input signal and the reference input signal. In the adaptation processing, the processing unit executes an FIR filter processing for processing the reference input signal using the FIR filter, an output processing for outputting, as the output signal, a residual between the primary input signal and the reference input signal processed by the FIR filter processing, and an update processing for updating tap coefficients of the FIR filter based on the residual, and executes a recalculation processing for executing the FIR filter processing, the output processing, and the update processing using the updated tap coefficients for the current frequency bin of the first signal a predetermined number of times before taking the positive frequency component of the next frequency bin of the first signal as the primary input signal.

[0081] <Feature 4> A signal processing device (200) includes: a transform unit (210) that Fourier transforms a beat signal (Bw) representing a time domain signal generated by mixing a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that reflects a transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave in a quadrature mixer (105) into a first signal (Bwf1) in the frequency domain, whose frequency components are represented for each frequency bin; and a processing unit (220) that has an adaptive filter (221) including an FIR filter (222) and generates an interference-removed signal (Ts) in which an interference signal component (IFIf) is removed from the first signal. The processing unit performs adaptive processing that sequentially uses each positive frequency component of the first signal as a primary input signal of the adaptive filter, sequentially uses each negative frequency component of the first signal corresponding to each positive frequency component as a reference input signal of the adaptive filter, and outputs an output signal based on the primary input signal and the reference input signal. In the adaptive processing, the processing unit executes: an FIR filter processing for processing the primary input signal using the FIR filter; an output processing for outputting, as the output signal, a residual between the primary input signal and the reference input signal processed by the FIR filter processing; and an update processing for updating tap coefficients of the FIR filter based on the residual. As the adaptive processing, the processing unit executes: a first adaptive processing in which the positive frequency components of the first signal are used as the primary input signal in order from a frequency bin corresponding to a short distance toward a frequency bin corresponding to a long distance; and a second adaptive processing in which the positive frequency components of the first signal are used as the primary input signal in order from a frequency bin corresponding to a medium distance toward a frequency bin corresponding to a short distance. The processing unit outputs, as the interference-removed signal, a signal obtained by joining the signal output by the output processing of the first adaptive processing and the signal output by the output processing of the second adaptive processing.

[0082] <Mode 5> In the radar device of any one of Modes 1 to 4, the conversion unit may perform a Fourier transform on the beat signal to generate a second signal (Bwf2) in the frequency domain in which frequency components are represented for each frequency bin, and the processing unit may execute a determination process to determine whether a signal strength difference between a positive frequency component and a negative frequency component in a high frequency region of the second signal, which represents a frequency region higher than a predetermined frequency, is equal to or less than a predetermined reference value, and execute the adaptive process when the signal strength difference is equal to or less than the reference value.

[0083] <Form 6> A radar system (100) includes a signal processing device according to any one of Forms 1 to 5, a transmitting unit (102) that transmits the transmission wave to the target based on the transmission signal, a receiving unit (103) that receives the reception signal, the quadrature mixer, and a measuring unit that measures the target based on the output signal. [Explanation of symbols]

[0084] 100... radar system, 101... signal generation unit, 102... transmission unit, 103... reception unit, 105... quadrature mixer, 106... filter unit, 107... analog-to-digital conversion unit, 200... signal processing device, 210... conversion unit, 220... processing unit, 221... adaptive filter, 222... FIR filter, 230... measurement unit, Bw... beat signal, Bwf1... first signal, Bwf2... second signal, Dw... received signal, Ew... electromagnetic wave, IFIf... interference signal component, OB... target, Ts... signal after interference removal

Claims

1. A signal processing device (200), a transform unit (210) that performs a Fourier transform on a beat signal (Bw) representing a time domain signal generated by mixing, in an orthogonal mixer (105), a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that has reflected the transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave, into a first signal (Bwf1) in the frequency domain in which frequency components are represented for each frequency bin; a processing unit (220) having an adaptive filter (221) including an FIR filter (222) and generating an interference-removed signal (Ts) in which an interference signal component (IFIf) is removed from the first signal, the processing unit performs an adaptation process in which each positive frequency component of the first signal is used in turn as a main input signal of the adaptive filter, and each negative frequency component of the first signal corresponding to each positive frequency component is used in turn as a reference input signal of the adaptive filter, and outputs an output signal based on the main input signal and the reference input signal; In the adaptation processing, the processing unit FIR filtering processing of processing the reference input signal by the FIR filter; an output process for outputting, as the output signal, the residual between the primary input signal and the reference input signal processed by the FIR filter process; an update process for updating tap coefficients of the FIR filter based on the residual; changing a step size parameter for updating the tap coefficients based on a bin number of a frequency bin of the first signal; Signal processing device.

2. 2. The signal processing device according to claim 1, The signal processing device wherein the processing unit monotonically increases the step size parameter with respect to the bin number.

3. A signal processing device (200), a transform unit (210) that performs a Fourier transform on a beat signal (Bw) representing a time domain signal generated by mixing, in an orthogonal mixer (105), a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that has reflected the transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave, into a first signal (Bwf1) in the frequency domain in which frequency components are represented for each frequency bin; a processing unit (220) having an adaptive filter (221) including an FIR filter (222) and generating an interference-removed signal (Ts) in which an interference signal component (IFIf) is removed from the first signal, the processing unit performs an adaptation process in which each positive frequency component of the first signal is used in turn as a main input signal of the adaptive filter, and each negative frequency component of the first signal corresponding to each positive frequency component is used in turn as a reference input signal of the adaptive filter, and outputs an output signal based on the main input signal and the reference input signal; In the adaptation processing, the processing unit FIR filtering processing of processing the reference input signal by the FIR filter; an output process for outputting, as the output signal, the residual between the primary input signal and the reference input signal processed by the FIR filter process; an update process for updating tap coefficients of the FIR filter based on the residual; a signal processing device that executes a recalculation process for executing the FIR filter process, the output process, and the update process using the updated tap coefficients for a current frequency bin of the first signal a predetermined number of times before using the positive frequency component of a next frequency bin of the first signal as the main input signal.

4. A signal processing device (200), a transform unit (210) that performs a Fourier transform on a beat signal (Bw) representing a time domain signal generated by mixing, in an orthogonal mixer (105), a received signal (Dw) obtained by receiving a reflected wave from a target (OB) that has reflected the transmitted wave and a transmitted signal (Tw) for transmitting the transmitted wave, into a first signal (Bwf1) in the frequency domain in which frequency components are represented for each frequency bin; a processing unit (220) having an adaptive filter (221) including an FIR filter (222) and generating an interference-removed signal (Ts) in which an interference signal component (IFIf) is removed from the first signal, the processing unit performs an adaptation process in which each positive frequency component of the first signal is used in turn as a main input signal of the adaptive filter, and each negative frequency component of the first signal corresponding to each positive frequency component is used in turn as a reference input signal of the adaptive filter, and outputs an output signal based on the main input signal and the reference input signal; In the adaptation processing, the processing unit FIR filtering processing of processing the reference input signal by the FIR filter; an output process for outputting, as the output signal, the residual between the primary input signal and the reference input signal processed by the FIR filter process; an update process for updating tap coefficients of the FIR filter based on the residual; As the adaptation processing, a first adaptation processing is performed in which the positive frequency components of the first signal are used as the main input signal in order from a frequency bin corresponding to a short distance to a frequency bin corresponding to a long distance, and a second adaptation processing is performed in which the positive frequency components of the first signal are used as the main input signal in order from a frequency bin corresponding to a medium distance to a frequency bin corresponding to the short distance, a signal obtained by splicing the signal output by the output processing of the first adaptive processing and the signal output by the output processing of the second adaptive processing together is output as the interference-removed signal; Signal processing device.

5. 5. A signal processing device according to claim 1, the converter performs a Fourier transform on the beat signal to generate a second signal (Bwf2) in the frequency domain in which frequency components are represented for each frequency bin; the processing unit executes a determination process to determine whether a signal strength difference between a positive frequency component and a negative frequency component in a high frequency range of the second signal, the high frequency range representing a frequency range higher than a predetermined frequency, is equal to or less than a predetermined reference value; The signal processing device performs the adaptive processing when the signal strength difference is equal to or less than the reference value.

6. A radar system (100), comprising: A signal processing device according to any one of claims 1 to 4; a transmitting unit (102) that transmits the transmission wave to the target based on the transmission signal; a receiving unit (103) for receiving the received signal; the quadrature mixer; a measurement unit that measures the target based on the output signal.

7. A radar system (100), comprising: The signal processing device according to claim 5 ; a transmitting unit (102) that transmits the transmission wave to the target based on the transmission signal; a receiving unit (103) for receiving the received signal; the quadrature mixer; a measurement unit that measures the target based on the output signal.

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