JP5422140B2 - Target detection device - Google Patents

Description

  The present invention relates to a target detection apparatus that detects a target from a received signal, and more particularly to a technique for detecting a target using a two-dimensional discrete wavelet transform (hereinafter abbreviated as “DWT; Discrete Wavelet Transform”).

  2. Description of the Related Art Conventionally, for example, a target detection device that is provided in a radar device, receives a reflected wave that is transmitted and reflected by a transmitted pulse signal, and detects a target based on the received reflected wave is known. In such a target detection apparatus, a plurality of reflected waves (hits) are received and integrated to improve the SN ratio (Signal to Noise Power Ratio). However, for targets that move at high speed (hereinafter referred to as “high-speed targets”), there is an upper limit to the number of hits that can be integrated due to deviations in the target range direction. Inferior detection performance.

  FIG. 15 is a block diagram showing a configuration of a conventional target detection apparatus. The target detection apparatus includes a coherent integration circuit 101, a maximum value extraction circuit 102, a constant false alarm rate (hereinafter referred to as “CFAR: Constant False Alarm Rate”) circuit 5, and a detection circuit 6.

  This target detection apparatus operates as follows. That is, a reception signal obtained by receiving a reflected wave with an antenna (not shown) is sent to the coherent integration circuit 101. The coherent integration circuit 101 performs coherent integration, that is, fast Fourier transform (hereinafter abbreviated as “FFT”), and sends the received signal to the maximum value extraction circuit 102. The maximum value extraction circuit 102 extracts the maximum value from the signal sent from the coherent integration circuit 101 and sends it to the CFAR circuit 5.

  The CFAR circuit 5 generates a signal in which the false alarm probability is suppressed to a certain low level with respect to the signal sent from the maximum value extraction circuit 102 and sends the signal to the detection circuit 6. Note that CFAR is described in Non-Patent Document 1, for example. FIG. 16 is a block diagram illustrating a configuration of a linear CFAR circuit that performs normalization by arithmetic mean as an example of the CFAR circuit 5. The CFAR circuit 5 includes a delay circuit 51, an addition circuit 52, an averaging processing circuit 53, and a division circuit 54.

  The delay circuit 51 delays the input signal xi and then sends it to the adder circuit 52 and the divider circuit 54. The adder circuit 52 adds the N pieces of data sent from the delay circuit 51 during a certain period, and sends it to the averaging processing circuit 53. The averaging processing circuit 53 calculates the average value of the N pieces of data sent from the adding circuit 52 and sends it to the dividing circuit 54. The division circuit 54 divides the data sent from the delay circuit 51 by the average value sent from the averaging processing circuit 53 and sends the division result to the detection circuit 6 as a CFAR output. The CFAR circuit 5 may be realized by a logarithmic CFAR circuit that performs normalization with a geometric mean.

The detection circuit 6 compares the signal sent from the CFAR circuit 5 in which the false alarm probability is suppressed to a certain low level with a predetermined threshold level, detects the target based on the comparison result, and detects the detected result. Output as detection value.
Sekine, "Radar signal processing technology", IEICE, pp.96-106 (1991)

  However, the above-described conventional target detection apparatus has the following problems. FIG. 17 shows a state of a target appearing in a received signal in each of a plurality of PRIs (Pulse Repetition Interval). In the case of a high-speed target or when the target speed is larger than the range cell resolution, there is a problem that a range walk that is a deviation from the range cell occurs, an integration loss occurs, and the target detection performance deteriorates. Further, when the high-speed target is a small target, the SN ratio is insufficient in the integration processing only within the CPI (Coherent Processing Interval), and the target may not be detected.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a target detection device that can improve target detection performance even if the high-speed target is a small target.

The first invention includes an FFT circuit for each CPI that performs Fourier transform on input data at every coherent processing interval (CPI), and a range-angle axis for each CPI obtained by Fourier transform by an FFT circuit for each CPI. An inter-frame video integration circuit that generates a frame indicating a target position and generates a maximum value or an added signal between the frames, and a two-dimensional DWT circuit that performs a two-dimensional discrete wavelet transform on the output of the inter-frame video integration circuit A target is detected by performing predetermined processing on the output of the two-dimensional DWT circuit.

Furthermore, the second invention is a target range extraction circuit for extracting a target range where a target exists based on the output of the two-dimensional DWT circuit, and input data obtained for transmission / reception with respect to the target range extracted by the target range extraction circuit. And an FFT circuit that performs fast Fourier transform, and a target is detected by performing predetermined processing on the output of the FFT circuit.

  According to the target detection device of the present invention, it is possible to provide a target detection device that can improve target detection performance even if the high-speed target is a small target.

  Specifically, according to the first invention, the two-dimensional DWT can be decomposed into a signal in the vertical direction, the horizontal direction, or the diagonal direction, so that the most efficient extraction method is selected in advance according to the signal. The signal can be extracted efficiently. As a result, the target detection performance can be improved even if the high speed target is a small target.

  Further, according to the second invention, a target can be detected using a signal that is most efficient for detecting a target signal among signals decomposed by the two-dimensional DWT. As a result, the target detection performance can be improved even if the high speed target is a small target.

  Further, according to the third invention, the signal is decomposed into a signal in the vertical direction, the horizontal direction or the diagonal direction by the two-dimensional DWT, and the maximum value is used, so that the spread of the signal on the time-frequency axis is not known. However, the most efficient extraction method can be automatically selected. As a result, the target detection performance can be improved even if the high speed target is a small target.

  In addition, according to the fourth invention, when a false alarm other than a desired target occurs on the axis of the wavelet expansion coefficient of the two-dimensional DWT, it is highly possible that the target signal will straddle adjacent cells. Even so, it is possible to reduce the false alarm and increase the probability that only the target can be detected. As a result, the target detection performance can be improved even if the high speed target is a small target.

  According to the fifth invention, when a false alarm other than the desired target occurs on the axis of the wavelet expansion coefficient of the two-dimensional DWT, it is highly possible that the target signal will straddle adjacent cells. Even so, it is possible to reduce the false alarm and increase the probability that only the target can be detected. As a result, the target detection performance can be improved even if the high speed target is a small target.

  According to the sixth aspect of the invention, the target signal is added by the two-dimensional DWT using the data obtained by adding the frames, and the target is detected, so that the probability that the target can be detected can be improved. it can. As a result, the target detection performance can be improved even if the high speed target is a small target.

  Further, according to the seventh invention, the SN ratio can be improved by extracting the target range and performing multipulse integration within the limited range, so that the target can be detected efficiently. As a result, the target detection performance can be improved even if the high speed target is a small target.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or equivalent components as those of the conventional target detection apparatus described in the background art section are denoted by the same reference numerals as those used in the background art section, and description thereof is omitted or simplified.

  FIG. 1 is a block diagram illustrating the configuration of the target detection apparatus according to the first embodiment of the present invention. This target detection apparatus includes an FFT circuit 1 for each CPI, an inter-CPI video integration circuit 2, a two-dimensional DWT circuit 3, a maximum value detection and determination cell range designation circuit 4, a CFAR circuit 5, and a detection circuit 6. Among these components, the CFAR circuit 5 and the detection circuit 6 are the same as those described in the background art section.

  The per-CPI FFT circuit 1 performs fast Fourier transform (FFT) on input data for each CPI. Thereby, data representing the target position on the range-Doppler frequency axis, that is, the time-frequency axis as shown in FIG. 2A is obtained. Data representing the target position obtained by the FFT circuit 1 for each CPI is sent to the inter-CPI video integration circuit 2.

  The inter-CPI video integration circuit 2 sequentially stores data representing the target position sent from the FFT circuit 1 for each CPI, and performs maximum value extraction or addition operation on the stored data representing the target position for each CPI. Then, synthetic CPI data as shown in FIG. The synthesized CPI data generated by the inter-CPI video integration circuit 2 is sent to the two-dimensional DWT circuit 3.

  The two-dimensional DWT circuit 3 performs two-dimensional DWT on the synthesized CPI data in order to integrate the target signal portion of the synthesized CPI data sent from the inter-CPI video integration circuit 2.

  Here, the principle of wavelet transform (DWT) will be described. First, the one-dimensional DWT will be described. The wavelet transform used when detecting a target is a correlation process for input data as shown in FIG. 3A while changing parameters (shift R, scale f) of a wavelet transform kernel (for example, Mexican hat). It can be said that the fitting process is performed to obtain an output of high wavelet transform data as shown in FIG.

This can be expressed discretely as shown in FIG. That is, the wavelet transform approximates an input signal waveform with a scaling coefficient and a wavelet expansion function, and the degree of approximation differs depending on the level. When this is represented by a filter, it corresponds to a filter as shown in FIG. 5, which corresponds to extraction with a fine temporal resolution at a high frequency and with a coarse temporal resolution at a low frequency. The characteristics of this filter are as described in, for example, “Nakano et al.,“ Signal Processing and Image Processing Using Wavelets ”, Kyoritsu Shuppan Co., Ltd., pp. 49-70, pp. 101-110 (1999)”. It can represent with Formula (1)-(3).

here,
fj: j-level approximation function (j = 1 to J)
gj: j level expansion function sk: scaling expansion coefficient (k = 1 to K)
wk: Wavelet expansion coefficient φ: Scaling function ψ: Mother wavelet function pk: Sequence determined by mother wavelet function *: Complex conjugate Here, w shown in equation (5) is an approximate function and an actual waveform at each level j And a wavelet expansion coefficient. Since the wavelet expansion coefficient includes a signal component, a signal can be extracted using the wavelet expansion coefficient.

Next, the two-dimensional discrete wavelet transform used in Embodiment 1 of the present invention will be described. The two-dimensional discrete wavelet transform performs a one-dimensional discrete wavelet transform for each of the two axis directions. For example, “Nakano et al.,“ Signal processing and image processing using wavelets ”, Kyoritsu Shuppan Co., Ltd., pp. 71-73 (1999) ”, it can be expressed by the following equations (7) to (10).

Here, if the subscript is omitted,
s; scaling expansion coefficient w; wavelet expansion coefficient p: sequence determined by mother wavelet function q; (k: number of the sequence indicating the wavelet)
j: wavelet expansion level m, n; two-dimensional axis number *; complex conjugate wavelet expansion coefficients when the superscripts are h, v, and d are wh, wv, and wd, respectively. The wavelet expansion coefficients wh, wv, and wd each have a property that the value increases when there is a signal continuous in the horizontal axis direction, a signal continuous in the vertical axis direction, and a signal continuous in the diagonal direction. . This is shown in FIG. The two-dimensional DWT circuit 3 sends the wavelet expansion coefficient obtained by the two-dimensional discrete wavelet transform to the maximum value detection and determination cell range designation circuit 4.

  The maximum value detection / determination cell range designation circuit 4 extracts the maximum value of the wavelet expansion coefficient from the signal shown in FIG. 2B by using the above-described property, and designates the determination cell range of the CFAR. . The determination cell range specified by the maximum value detection and determination cell range specifying circuit 4 is sent to the CFAR circuit 5. The CFAR circuit 5 performs the CFAR process in the determination cell range sent from the maximum value detection and determination cell range specifying circuit 4.

  Next, the operation of the target detection apparatus according to Embodiment 1 of the present invention configured as described above will be described with reference to the flowchart shown in FIG.

  First, signal transmission / reception is performed (step S11). Next, fast Fourier transform (FFT) is performed (step S12). That is, the FFT circuit 1 for each CPI performs fast Fourier transform on the input data in one CPI obtained by the transmission / reception in step S11, and sends it to the inter-CPI video integration circuit 2. The inter-CPI video integration circuit 2 sequentially stores data representing the target position sent from the FFT circuit 1 for each CPI.

  Next, it is checked whether or not all CPIs have been completed (step S13). If it is determined in step S13 that all the CPIs have not been completed, then the CPI is changed (step S14). That is, the state is changed so that processing for the next CPI is performed. Then, it returns to step S11 and the process mentioned above is repeated.

  If it is determined in step S13 that all the CPIs have been completed, then inter-CPI integration is performed (step S15). That is, the inter-CPI video integration circuit 2 performs the maximum value extraction or addition operation of the data representing the target position for each CPI received from the CPI FFT circuit 1 and stored, as shown in FIG. Composite CPI data is generated and sent to the two-dimensional DWT circuit 3.

  Next, two-dimensional DWT is performed (step S16). That is, the two-dimensional DWT circuit 3 performs two-dimensional DWT on the synthesized CPI data sent from the inter-CPI video integration circuit 2. The wavelet expansion coefficient obtained by the two-dimensional DWT is sent to the maximum value detection and determination cell range designation circuit 4.

  Next, maximum value detection and determination cell range designation are performed (step S17). That is, the maximum value detection and determination cell range specifying circuit 4 extracts the maximum value of the wavelet expansion coefficient from the signal shown in FIG. 2B, specifies the CFAR determination cell range, and specifies the specified determination cell range. Is sent to the CFAR circuit 5.

  Next, CFAR processing and detection processing are performed (step S18). That is, the CFAR circuit 5 performs the CFAR process in the determination cell range indicated by the data transmitted from the maximum value detection and determination cell range specifying circuit 4 and sends the result to the detection circuit 6. The detection circuit 6 compares the signal sent from the CFAR circuit 5 in which the false alarm probability is suppressed to a certain low level with a predetermined threshold level, detects the target based on the comparison result, and detects the detected result. Output as detection value.

  Next, it is checked whether or not the processing for all the determination cell ranges has been completed (step S19). If it is determined in step S19 that the processing for all the determination cell ranges has not been completed, then the cell range is changed (step S20). That is, the state is changed so that processing for the next cell range is performed. Then, it returns to step S18 and the process mentioned above is repeated. If it is determined in step S19 that the processing for all the determination cell ranges has been completed, the operation of the target detection apparatus is ended.

  As described above, according to the target detection apparatus according to the first embodiment of the present invention, the two-dimensional DWT can be decomposed into signals in the vertical direction, the horizontal direction, or the diagonal direction, so that the most efficient extraction is performed according to the signal. By selecting a method in advance, a signal can be extracted efficiently. As a result, the target detection performance can be improved even if the high speed target is a small target.

  The target detection apparatus according to the second embodiment of the present invention is the target detection apparatus according to the first embodiment. The target detection apparatus according to the first embodiment predicts the spread direction of the target signal in advance, and the wavelet expansion coefficient wh, wv, or wd of the two-dimensional DWT This is a choice.

  The configuration of the target detection apparatus according to the second embodiment is set so as to select one of the two-dimensional DWT wavelet expansion coefficients wh, wv, or wd for the maximum value detection and determination cell range designation circuit 4. Is the same as the configuration of the target detection apparatus according to the first embodiment shown in FIG.

  The maximum value detection and determination cell range designation circuit 4 determines the CFAR using one of the preset wavelet expansion coefficients wh, wv, or wd among the wavelet expansion coefficients sent from the two-dimensional DWT circuit 3. Specify a cell range. The determination cell range specified by the maximum value detection and determination cell range specifying circuit 4 is sent to the CFAR circuit 5.

  The operation of the target detection apparatus according to the second embodiment configured as described above has been described with reference to the flowchart of FIG. 7 except that the maximum value detection and determination cell range designation circuit 4 performs the above-described operation. The operation is the same as that of the target detection apparatus according to the first embodiment.

  As described above, according to the target detection apparatus according to the second embodiment of the present invention, the target can be detected using the signal most efficient for detecting the target signal among the signals decomposed by the two-dimensional DWT. it can. As a result, the target detection performance can be improved even if the high speed target is a small target.

  The target detection apparatus according to the third embodiment of the present invention uses the wavelet expansion coefficient having the maximum value among the wh, wv, or wd of the wavelet expansion coefficient of the two-dimensional DWT in the target detection apparatus according to the first embodiment. It is a thing.

  In the configuration of the target detection apparatus according to the third embodiment, the maximum value detection and determination cell range specifying circuit 4 uses a wavelet expansion coefficient in which the maximum value exists among the wavelet expansion coefficients wh, wv, or wd of the two-dimensional DWT. 1 is the same as the configuration of the target detection apparatus according to the first embodiment shown in FIG.

  As described above, the maximum value detection and determination cell range specifying circuit 4 specifies the determination cell range using the wavelet expansion coefficient having the maximum value among the wavelet expansion coefficients sent from the two-dimensional DWT circuit 3. . The determination cell range specified by the maximum value detection and determination cell range specifying circuit 4 is sent to the CFAR circuit 5.

  The operation of the target detection apparatus according to the third embodiment configured as described above has been described with reference to the flowchart of FIG. 7 except that the maximum value detection and determination cell range specification circuit 4 performs the above-described operation. The operation is the same as that of the target detection apparatus according to the first embodiment.

  As described above, according to the target detection apparatus according to the third embodiment of the present invention, the signal is decomposed into a signal in the vertical direction, the horizontal direction, or the diagonal direction by the two-dimensional DWT and the maximum value is used. Even if the spread on the time-frequency axis is not known, the most efficient extraction method can be automatically selected. As a result, the target detection performance can be improved even if the high speed target is a small target.

  The target detection apparatus according to the fourth embodiment of the present invention uses the maximum value of the two-dimensional DWT wavelet expansion coefficient when there is a possibility that the target signal straddles adjacent cells, and N = N1 × N2 around the target signal. (N, N1, and N2 are positive integers) When M (M is a positive integer, M ≦ N) or more cells exceed the threshold, the target is detected. .

  FIG. 8 is a block diagram illustrating the configuration of the target detection apparatus according to the fourth embodiment. The target detection apparatus according to the fourth embodiment is configured by replacing the detection circuit 6 of the target detection apparatus shown in FIG. 1 with an M / N detection circuit 7.

  FIG. 9 is a diagram for explaining the operation of the target detection apparatus according to the fourth embodiment. First, the inter-CPI video integration circuit 2 generates synthesized CPI data on the PRI-frequency axis, that is, on the time-frequency axis as shown in FIG. 9A and sends it to the two-dimensional DWT circuit 3. The two-dimensional DWT circuit 3 performs two-dimensional discrete wavelet transform on the signal sent from the inter-CPI video integration circuit 2 as input data as shown in FIG. 9B, and as shown in FIG. 9C. The signal is sent to the maximum value detection / judgment cell range designation circuit 4.

  The maximum value detection / judgment cell range designation circuit 4 obtains the maximum value from the wavelet expansion coefficients W1v, W1h, and W1d, and as shown in FIG. 9D, N1 × N2 ranges around the maximum value. A signal representing the cell is sent to the M / N detection circuit 7 via the CFAR circuit 5.

  The M / N detection circuit 7 compares a signal representing N cells sent from the maximum value detection and determination cell range specification circuit 4 via the CFAR circuit 5 with a predetermined threshold level, and M or more are predetermined. If the threshold level is exceeded, the target is detected and the detection result is output as a detection value.

  The operation of the target detection apparatus according to the fourth embodiment configured as described above is the same as that of FIG. 7 except that the maximum value detection and determination cell range specifying circuit 4 and the M / N detection circuit 7 perform the above-described operations. This is the same as the operation of the target detection apparatus according to the first embodiment described with reference to the flowchart.

  As described above, according to the target detection apparatus according to the fourth embodiment of the present invention, the target signal is likely to straddle adjacent cells on the axis of the wavelet expansion coefficient of the two-dimensional DWT. Even if a false alarm other than the target occurs, the probability that only the target can be detected is reduced by reducing the false alarm. As a result, the target detection performance can be improved even if the high speed target is a small target.

  The target detection apparatus according to the fifth embodiment of the present invention extracts from the maximum of the extreme values of the wavelet expansion coefficient of the two-dimensional DWT to the Lth (L is a positive integer) in order to cope with the detection of a plurality of targets. In each extreme value, if there are N = N1 × N2 cells around the extreme value, and M or more cells exceed the threshold, the target is detected.

  The configuration of the target detection apparatus according to the fifth embodiment is the same as that of the target detection apparatus according to the fourth embodiment shown in FIG. 8 except for the operations of the maximum value detection and determination cell range designation circuit 4 and the M / N detection circuit 7. The same.

  The operation of the target detection apparatus according to the fifth embodiment will be described with reference to FIG. 9 described above. First, the inter-CPI video integration circuit 2 generates synthesized CPI data on the PRI-frequency axis, that is, on the time-frequency axis as shown in FIG. 9A and sends it to the two-dimensional DWT circuit 3. The two-dimensional DWT circuit 3 performs two-dimensional discrete wavelet transform on the signal sent from the inter-CPI video integration circuit 2 as input data as shown in FIG. 9B, and as shown in FIG. 9C. The signal is sent to the maximum value detection / judgment cell range designation circuit 4.

  The maximum value detection / judgment cell range designation circuit 4 obtains the maximum value from the wavelet expansion coefficients W1v, W1h, and W1d, and from the maximum values of the extreme values of the plurality of wavelet expansion coefficients as shown in FIG. A signal representing a cell in the range of N1 × N2 (= N) around each extreme value up to the Lth is sent to the M / N detection circuit 7 via the CFAR circuit 5.

  For each extreme value, the M / N detection circuit 7 compares a signal representing N cells sent from the maximum value detection and determination cell range designation circuit 4 via the CFAR circuit 5 with a predetermined threshold level, If M or more exceeds a predetermined threshold level, the target is detected and the detection result is output as a detection value.

  The operation of the target detection apparatus according to the fifth embodiment configured as described above is the same as that shown in FIG. 7 except that the maximum value detection and determination cell range specifying circuit 4 and the M / N detection circuit 7 perform the above-described operations. This is the same as the operation of the target detection apparatus according to the first embodiment described with reference to the flowchart.

  As described above, according to the target detection apparatus according to the fifth embodiment of the present invention, the target signal is likely to straddle adjacent cells on the axis of the wavelet expansion coefficient of the two-dimensional DWT. Even if a false alarm other than the target occurs, it is possible to reduce the false alarm, detect only the target, and use a plurality of extreme values, thereby increasing the probability of detecting a plurality of targets. . As a result, the target detection performance can be improved even if the high speed target is a small target.

  The target detection apparatus according to the sixth embodiment of the present invention is not a maximum value extraction or addition data of a plurality of CPIs as in the target detection apparatus according to the first embodiment, but a target position (range-cross range axis or range-angle axis). A target signal is added to the data obtained by extracting or adding the maximum values between a plurality of frames indicating a target by two-dimensional DWT.

  FIG. 10 is a block diagram illustrating the configuration of the target detection apparatus according to the sixth embodiment of the present invention. This target detection apparatus is configured by replacing the inter-CPI video integration circuit 2 of the target detection apparatus according to the first embodiment with an inter-frame video integration circuit 8.

  The per-CPI FFT circuit 1 performs fast Fourier transform (FFT) on input data for each CPI. Thereby, data representing the target position on the range-angle axis as shown in FIG. Data representing the target position obtained by the FFT circuit 1 for each CPI is sent to the inter-frame video integration circuit 8.

  The inter-frame video integration circuit 8 sequentially stores data representing the target position sent from the CPI-by-CPI FFT circuit 1, and performs the maximum value extraction or addition operation of the stored data representing the target position for each CPI. Then, synthetic CPI data as shown in FIG. 11B is generated. The synthesized CPI data generated by the interframe video integration circuit 8 is sent to the two-dimensional DWT circuit 3.

  Next, the operation of the target detection apparatus according to Embodiment 6 of the present invention configured as described above will be described with reference to the flowchart shown in FIG.

  First, transmission / reception is performed (step S21). Next, fast Fourier transform (FFT) is performed (step S12). That is, the FFT circuit 1 for each CPI performs fast Fourier transform on input data in one CPI obtained by transmission / reception in step S11, generates data representing a target position on the range-angle axis, and generates an inter-frame video integration circuit 8 Send to. The inter-frame video integration circuit 8 sequentially stores data representing the target position sent from the FFT circuit 1 for each CPI.

  Next, it is checked whether or not the search range has ended (step S23). If it is determined in step S23 that the search range has not ended, then the beam position is changed (step S24). That is, the search range is changed so that processing for the next beam position is performed. Then, it returns to step S21 and the process mentioned above is repeated.

  If it is determined in step S23 that the search range has ended, it is then checked whether or not the number of frames has ended (step S25). If it is determined in step S25 that the number of frames has not ended, then the frame number is changed (step S26). That is, the frame number is changed so that processing for the next frame is performed. Then, it returns to step S21 and the process mentioned above is repeated.

  If it is determined in step S25 that the number of frames has been completed, then inter-frame integration is performed (step S27). That is, the inter-frame video integration circuit 8 performs the maximum value extraction or addition operation of the data representing the target position for each frame received from the CPI FFT circuit 1 and stored, as shown in FIG. Composite CPI data is generated and sent to the two-dimensional DWT circuit 3.

  Next, two-dimensional DWT is performed (step S28). That is, the two-dimensional DWT circuit 3 uses the wavelet expansion coefficient obtained by performing the two-dimensional DWT on the synthesized CPI data sent from the inter-frame video integration circuit 8 as a maximum value detection and determination cell range designation circuit. Send to 4.

  Next, maximum value detection and determination cell range specification are performed (step S29). That is, the maximum value detection and determination cell range specifying circuit 4 extracts the maximum value of the wavelet expansion coefficient from the signal shown in FIG. 11B, specifies the CFAR determination cell range, and specifies the specified determination cell range. Is sent to the CFAR circuit 5.

  Next, CFAR processing and detection processing are performed (step S18). That is, the CFAR circuit 5 performs the CFAR process in the determination cell range indicated by the data sent from the maximum value detection and determination cell range specifying circuit 4 and sends the result to the detection circuit 6. The detection circuit 6 compares the signal sent from the CFAR circuit 5 in which the false alarm probability is suppressed to a certain low level with a predetermined threshold level, detects the target based on the comparison result, and detects the detected result. Output as detection value.

  As described above, according to the target detection apparatus according to the sixth embodiment of the present invention, since the target signal is added by the two-dimensional DWT using the data obtained by adding the frames, the target is detected. The probability that the target can be detected can be improved. As a result, the target detection performance can be improved even if the high speed target is a small target.

  Although the target detection apparatus according to the first to sixth embodiments described above is configured to detect a target using the two-dimensional DWT as it is, the target detection apparatus according to the seventh embodiment of the present invention is a two-dimensional DWT. A target range is extracted based on the result, signals are transmitted / received again within the extracted range, and integration is performed efficiently to detect the target with higher accuracy.

  FIG. 13 is a block diagram illustrating a configuration of the target detection device according to the seventh embodiment of the present invention. In this target detection device, a target range extraction circuit 9, a radar control device 10, and an FFT circuit 11 are added between the maximum value detection and determination cell range designation circuit 4 and the CFAR circuit 5 of the target detection device according to the sixth embodiment. Has been configured.

  The target range extraction circuit 9 extracts the target range based on the signal output from the maximum value detection and determination cell range designation circuit 4. A signal representing the target range extracted by the target range extraction circuit 9 is sent to the radar control device 10.

  The radar control device 10 transmits and receives signals toward the target range indicated by the signal sent from the target range extraction circuit 9. A reception signal transmitted from the target in the target range by transmission / reception by the radar control device 10 is input to the FFT circuit 11 as input data 2. The FFT circuit 11 performs fast Fourier transform on the input data 2 and sends it to the CFAR circuit 5.

  Next, the operation of the target detection apparatus according to Embodiment 1 of the present invention configured as described above will be described with reference to the flowchart shown in FIG. In addition, the same code | symbol as the code | symbol used in FIG. 12 is attached | subjected to the step which performs the process same as the flowchart which shows operation | movement of the target detection apparatus based on Example 6 shown in FIG. 12, and description is abbreviate | omitted.

  First, the process of step S21-step S28 is the same as the process shown in the flowchart which shows operation | movement of the target detection apparatus based on Example 6 shown in FIG. In step S29, maximum value detection and determination cell range specification are performed. That is, the maximum value detection and determination cell range specifying circuit 4 extracts the maximum value of the wavelet expansion coefficient from the signal shown in FIG. 11B, specifies the CFAR determination cell range, and specifies the specified determination cell range. Is sent to the target range extraction circuit 9.

  Next, target range extraction is performed (step S31). That is, the target range extraction circuit 9 extracts the target range based on the signal sent from the maximum value detection and determination cell range designation circuit 4 and sends a signal indicating that to the radar control device 10.

  Next, transmission / reception is performed (step S32). That is, the radar control device 10 transmits / receives a signal toward the target range indicated by the signal transmitted from the target range extraction circuit 9. The received signal reflected by the target in the target range by the transmission / reception by the radar control device 10 is input to the FFT circuit 11 as the input data 2.

  Next, fast Fourier transform (FFT) is performed (step S33). That is, the FFT circuit 11 performs a Fourier transform on the input data 2 and sends the result to the CFAR circuit 5.

  Next, CFAR processing and detection processing are performed (step S34). That is, the CFAR circuit 5 performs CFAR processing on the signal sent from the FFT circuit 11 and sends the result to the detection circuit 6. The detection circuit 6 compares a signal with a low false alarm probability sent from the CFAR circuit 5 to a certain low level with a predetermined threshold level, detects a target based on the comparison result, and the detection result Is output as a detection value.

  As described above, according to the target detection device according to the seventh embodiment of the present invention, the SN ratio can be improved by extracting the target range and performing multi-pulse integration within the limited range, so that it is efficient. The target can be detected. As a result, the target detection performance can be improved even if the high speed target is a small target.

  In the target detection apparatus according to the first to sixth embodiments described above, the wavelet expansion coefficient of the two-dimensional DWT is configured to wavelet transform the input signal only once, but is configured to expand a plurality of times. You can also

  The present invention is applicable to a radar device or a receiving device that detects and tracks a small target that moves at high speed.

It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the video integration between CPI performed in the target detection apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the wavelet transformation performed in the target detection apparatus which concerns on Example 1 of this invention. It is a figure which shows the wavelet expansion coefficient of the wavelet transformation performed in the target detection apparatus which concerns on Example 1 of this invention. It is a figure which shows the time-frequency filter of the wavelet transformation performed in the target detection apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the input / output signal of the wavelet transform performed in the target detection apparatus which concerns on Example 1 of this invention. It is a flowchart for demonstrating operation | movement of the target detection apparatus which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 4 of this invention. It is a figure for demonstrating the wavelet transformation performed in the target detection apparatus which concerns on Example 4 of this invention. It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 6 of this invention. It is a figure for demonstrating the wavelet transformation performed in the target detection apparatus based on Example 6 of this invention. It is a flowchart for demonstrating operation | movement of the target detection apparatus which concerns on Example 6 of this invention. It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 7 of this invention. It is a flowchart for demonstrating operation | movement of the target detection apparatus which concerns on Example 7 of this invention. It is a block diagram which shows the structure of the conventional target detection apparatus. It is a block diagram which shows the detail of the CFAR circuit used with the conventional target detection apparatus. It is a figure which shows the mode of the target which appears in a received signal in each of several PRI transmitted / received in the conventional target detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 FFT circuit for every CPI 2 Video integration circuit between CPI 3 Two-dimensional DWT circuit 4 Maximum value and determination cell range designation circuit 5 CFAR circuit 6 Detection circuit 7 M / N detection circuit 8 Interframe video integration circuit 9 Target range extraction circuit 10 Radar Control device 11 FFT circuit

Claims (2)

An FFT circuit for each CPI that performs Fourier transform on input data for each coherent processing interval (CPI);
An inter-frame video integration circuit that generates a frame indicating a target position on the range-angle axis for each CPI obtained by Fourier transform by the FFT circuit for each CPI , and generates a maximum value or an added signal between the frames;
A two-dimensional DWT circuit for performing a two-dimensional discrete wavelet transform on the output of the inter-frame video integration circuit ;
A target detection apparatus for detecting a target by performing predetermined processing on an output of the two-dimensional DWT circuit. A target range extraction circuit that extracts a target range where a target exists based on the output of the two-dimensional DWT circuit;
  An FFT circuit that performs fast Fourier transform on input data obtained for transmission / reception with respect to the target range extracted by the target range extraction circuit;
  The target detection apparatus according to claim 1, wherein the target is detected by performing predetermined processing on the output of the FFT circuit.

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