JPH10239422A - Rador device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of undesired signal having several spectrum peaks by selecting a signal for obtaining the load of an adaptive filter, obtaining at least one or more load, and extracting a target signal from a reception beam synthesizing signal. SOLUTION: This device comprises a demodulator 11, undesired signal suppresser 12 with an adaptive filter, and target detector 13. A reception signal being an output signal of a demodulator 11 is first divided and transferred to an adaptive load control range bin selector. An undesired signal exists over ten range bins while most of target echos are within one range bin. When a target exists in the range bin to be treated, data for controlling the load of the adaptive filter is selected so that a target signal may not contained in the load control data. By the application of load control for minimizing the output power of undesired signal being the main component of reception signal, a filter amplitude characteristic according to the spectrum shape of undesired signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CW (Continuous Wave) using a modulated wave as a transmission wave.
The present invention relates to a radar apparatus for detecting a target signal by removing unnecessary reflected echoes (hereinafter, referred to as unnecessary signals) caused by clutter or the like other than a target signal by a filter.

[0002]

2. Description of the Related Art FIG. 7 shows Kondo et al .: "Suppression of radar clutter by a notch filter bank", IEICE Transactions B-II, vol. J78-BII, No. 9 (1
995) is a configuration diagram of a radar apparatus provided with unnecessary signal suppression means using a plurality of notch filters having different stopband widths disclosed in U.S. Pat. 7, 1 and 6 are antenna elements, 2 is a transmitter, 3 is a modulation signal generator, 7 is a receiver, 8 is an A / D converter, 10 is beam forming means, 11
Denotes demodulation means, 13 denotes target detection means, and 15 denotes unnecessary signal suppression means using a filter bank. In the following description,
For simplicity of expression, all signals are represented by complex signals. Each receiver amplifies a received signal in the RF band internally received by each antenna element, and performs phase detection to generate a complex video signal. This analog video signal is sampled at a fixed sampling period T in an A / D converter provided in each receiving device and is converted into a digital signal.

[0003] Here, the transmission wave is converted to FMCW (Frequency).
ncy Modulated Continuos W
ave) The operation will be described for an example of modulation by the ave method. F
In the MCW method, as shown in FIG.
, The reflected wave from the target located at the distance R is received with a delay of 2R / c with c as the speed of light, so the previous transmission frequency is received for a time corresponding to 2R / c. Will be. From this, assuming that the frequency difference between transmission and reception is fr, fr can be obtained from equation (1).

[0004]

(Equation 1)

[0005] Here, T _s is the frequency sweep time (frequency is Δ
f time required to change). Further, when Expression (1) is modified, Expression (2) is obtained, and the distance R to the target can be obtained from the frequency difference fr between transmission and reception.

[0006]

(Equation 2)

Accordingly, as demodulation processing, distance information (hereinafter referred to as range bins) can be obtained by performing a discrete Fourier transform on the output signal of the beam forming means. Can be obtained. Unwanted signal suppression processing is performed on the two-dimensional received signal data including the range and the time for each range bin. FIG. 8 is a processing block diagram of an unnecessary signal suppressing unit using a notch filter bank. First, the spectrum analysis unit 30 transforms an input signal into a frequency domain by performing a discrete Fourier transform. Spectrum analysis means 30
Estimating means 3 from the unnecessary signal spectrum obtained in
1 and the center frequency estimating means 32 estimate the bandwidth and the center frequency, respectively. Based on the estimated center frequency and bandwidth, the notch filter switching determination means 33
A notch filter having a stopband width most suitable for suppressing an unnecessary signal having the estimated bandwidth is selected. In the notch filter bank 34, a plurality of notch filters having different stopband widths are prepared, and unnecessary signal components in the received signal are suppressed by using the notch filters selected by the notch filter switching determination means 33. The signal after the unnecessary signal suppression processing is transferred to the target detection means 13 and the CFAR
(Constant False Alarm Rat
io) The target signal is detected by an automatic detection process such as the process.

However, when the received unnecessary signal is not a single peak but has a complicated spectrum shape having a plurality of peaks as shown in FIG. 10, the unnecessary signal suppressing means uses the unnecessary signal indicating the peak having the highest level. Only the components will work. Therefore, since other unnecessary signal components remain, there is a possibility that the false alarm probability will be increased in the target detection means at the subsequent stage.

[0009]

In a conventional radar apparatus provided with unnecessary signal suppressing means using a plurality of notch filters corresponding to unnecessary signals having a Gaussian spectrum, an unnecessary signal having a complicated spectrum shape is required. There is a problem that unremoved remains occur and the probability of false alarm increases in the target detection means.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and a plurality of spectral peaks are obtained by using an adaptive filter which performs weight adjustment with at least one range bin different from a range bin which performs unnecessary signal suppression processing. It is an object of the present invention to obtain a radar apparatus provided with unnecessary signal suppressing means capable of suppressing unnecessary signals having the above.

[0011]

In order to achieve the above object, a radar device according to the present invention comprises a transmitting means for radiating a transmission wave, and a reflection wave from a target, which is converted into a digital baseband signal. And a beam forming means for performing reception beam synthesis based on the digital baseband signal. In the configuration for performing target detection from the reception beam synthesis signal, a signal for calculating the weight of the adaptive filter from the reception beam synthesis signal is generated. An adaptive load adjustment range bin selecting means to be selected, and an adaptive load adjusting means for obtaining at least one load using the selected adaptive load adjustment signal are provided, and a target signal is extracted from the received beam combined signal. An adaptive filter type unnecessary signal suppressing unit is provided.

Further, the adaptive load adjustment range bin selecting means selects a range bin in a predetermined section as a range bin for adaptive load adjustment except for a range bin to be processed and a range bin adjacent to both sides of the range bin to be processed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a diagram showing a configuration of a radar apparatus according to the embodiment of the present invention. In the figure, 1 and 6 are antenna elements, 2 is a transmitter, 3 is a modulation signal generator, 7 is a receiver, 8 is an A / D converter, 10 is beam forming means, 11 is demodulation means, and 12 is the present invention. Unnecessary signal suppression means using an adaptive filter, which is an important component, 13 is a target detection means, and 14 is a signal processing device composed of these elements. Hereinafter, important components of the radar apparatus according to the present invention will be described in detail with reference to FIG. A feature of the present invention is that an unnecessary signal suppressing unit 1 using an adaptive filter is provided.
2 are provided, and therefore these operations will be mainly described.

The operation of the unnecessary signal suppressing means using the adaptive filter according to the first embodiment will be described with reference to FIGS. FIG. 2 is a processing block diagram of an unnecessary signal suppressing unit using the adaptive filter. In the figure, 23 is a delay unit for each unit sample, 15 is a complex adder, 16 is a complex subtractor, 17 is a complex multiplier, 18 is an adaptive weight adjustment range bin selection means, and 19 is a modified DMI (Direct Mat).
(Rix Inversion) algorithm. The received signal, which is the output signal of the demodulation means 11, is first branched and transferred to the adaptive weight adjustment range bin selection means 18. In general, unwanted signals exist over ten range bins, while target echoes often fall within one range bin. Therefore, the adaptive load adjustment range bin selecting means 18 selects data for adjusting the load of the adaptive filter so that the target signal is not included in the load adjustment data when the target exists in the range bin to be processed.

FIG. 3 is a block diagram showing the internal configuration of the adaptive load adjustment range bin selecting means 18. As shown in FIG. In the figure, 50 is a data buffer for temporarily storing data, 51 is a load adjustment data transfer means for controlling data output to the data buffer, 52 is a range bin counter for controlling a range bin to be processed, and 53 is a user Is a memory for storing parameters necessary for load adjustment that can be set arbitrarily. The load adjustment data transfer means 51
A range bin to be used for load adjustment is selected based on the range bin number transferred from the processing range bin counter 52 and the parameters NR and Δir transferred from the parameter storage memory 53. Then, the data buffer 50 is controlled so that the data corresponding to the range bin section is transferred to the adaptive load adjusting means 19 based on the modified DMI algorithm.

FIG. 4 shows the relationship between the processing range bin and the load adjustment range bin. 4, in order to avoid confusion, the horizontal direction is a range bin, and the time series is arranged in a direction perpendicular to the paper surface. The unnecessary signal suppression processing is sequentially performed, for example, from a short distance to a long distance in a range where the processing is required. In FIG. 4, the top figure is
The case where the range bin number ir is processed is shown, and the processing target range bin 21 and the load adjustment range bin 22 are represented by Δi
The interval is set by r. However, the number of load adjustment range bins depends on the characteristics of the received unnecessary signal in the distance direction. If the reception level and frequency characteristics change significantly in the distance direction, it is necessary to set a smaller number of load adjustment range bins. is there. Further, when performing signal processing near the edges of the processing range, that is, near the minimum range bin and the maximum range bin, the load adjustment range bin cannot be partially set, so that the number of data that can be used for adaptive load adjustment decreases. When the processing of the range bin number ir is completed, as shown in FIG. 4, the processing continues in the order of ir + 1, ir + 2, ir + 3, and all the range bins are processed.

The data selected by the adaptive load adjusting range bin selecting means 18 is transferred to the adaptive load adjusting means 19. In general, in an adaptive filter that updates the load for each input data sample, the load value changes with time (changes for each sample), so the phase characteristic of the filter is not linear. This means that an integration loss occurs in the S / N ratio improvement by the integration processing in the target detection means or the like and the target detection processing in the frequency domain, which is not preferable. Therefore,
It is necessary to fix the weight of the adaptive filter within the same processing range bin, and it is desirable to adopt a block processing type algorithm instead of a sequential processing type algorithm as the adaptive algorithm. Here, the adaptive filter weight adjustment is performed using an algorithm obtained by modifying the DMI algorithm which is a block processing type algorithm. FIG. 5 is a flowchart of the calculation performed by the adaptive load adjusting means 19 by the modified DMI algorithm when the processing range bin number is ir. Hereinafter, the load adjustment method will be described in comparison with this flowchart. The flow chart includes the processing contents of the adaptive load adjustment range bin selecting means 18 and the adaptive load adjusting means 19 based on the modified DMI algorithm in order to match with a mathematical expression described later.

Range bin number, time series sample number,
Assuming that the weights of the adaptive filters are i, n, and L, the received signal transferred to the unnecessary signal suppressing unit is x (n,
i). At this time, the load vector Wav,
It is assumed that the received signal vector D is expressed by Expressions (3) and (4), respectively (Step 60). Next, the autocorrelation matrix Rav and the cross-correlation vector Pav are obtained by using the data of the range bin selected by the adaptive load adjustment range bin selection means 18, that is, the data transferred from the data buffer 50. Steps 61 and 62 are operations relating to the adaptive load adjustment range bin selecting means 18. On the other hand, steps 63-6
At 8, in the range bin section selected by the adaptive load adjustment range bin selecting means 18, the time averaging operation is performed in a loop related to the variable k to improve the estimation accuracy of the autocorrelation matrix Rav and the cross-correlation vector Pav. The above flow of the load adjustment is expressed by the following equation. In the modified DMI algorithm, the autocorrelation matrix Rav and the cross-correlation vector P
av is represented by Expression (5) and Expression (6), respectively.

[0019]

(Equation 3)

Here, NS is a load calculation start sample number, NE is a load calculation end sample number, and is = i
r−NR−Δir, ie = ir + NR + Δir.
However, ir−Δir ≦ i ≦ ir + Δir is not used.
The autocorrelation matrix Rav and the cross-correlation vector P obtained by the above equation
Using av, the adaptive filter load vector Wav can be obtained from Expression (7).

[0021]

(Equation 4)

Using the adaptive weight calculated as described above, the output signal of the adaptive filter, that is, the output signal e (n, ir) of the unnecessary signal suppressing means can be obtained from equation (8).

[0023]

(Equation 5)

Equation (7) is an algorithm for directly calculating the Wiener-Hopf equation, and the load is adjusted so that the average power of the output signal e (n, ir) shown in equation (8) is minimized. The optimum load can be obtained.

Now, the Wiener-Hopf equation will be briefly described. For convenience of explanation, a variable i representing a range bin is excluded. Output signal e (n)
Is squared to give equation (9).

[0026]

(Equation 6)

Here, assuming that E [] is an averaging operation, an average value is defined as in equations (10a) and (10b). From equations (10a) and (10b), the average value on both sides of equation (9) is as shown in equation (11).

[0028]

(Equation 7)

Equation (12) can be obtained by partially differentiating W.

[0030]

(Equation 8)

When the load vector takes the optimum value Wo, equation (11) shows the minimum value. That is, Equation (11) is a quadratic function of the load vector W, and Equation (13) holds because the load vector that shows the minimum value in Equation (12) is the optimum value Wo. The autocorrelation vector R is a Hermitian matrix, and the equation (14) holds. Therefore, when the complex conjugate transposition of the equation (13) is taken and deformed, the optimal load vector can be obtained from the equation (15).

[0032]

(Equation 9)

As described above, the first embodiment of the present invention employs a method that does not suppress the target signal when adjusting the weight of the adaptive filter, and minimizes the output power of the unnecessary signal that is the main component of the received signal. By performing the load adjustment in such a manner as described above, it is possible to realize a filter amplitude characteristic according to the unnecessary signal spectrum shape. Therefore, it is possible to suppress an unnecessary signal having a complicated spectrum as shown in FIG.

In the above-described embodiment, the range between the processing range bin and the adaptive load adjustment range bin is at least 1 since the range side lobe of the target signal may be generated by performing the discrete Fourier transform by the demodulation means 11.
It is desirable to leave more than the range bin. That is, Δi in FIG.
The range bin data indicated by r is not used. However, as another embodiment, the range bin on both sides may be selected as the adaptive load adjustment range bin without providing Δir.

[0035]

As described above, according to the present invention, since the adaptive filter having the range bin selecting means for adjusting the load and the adaptive load adjusting means for obtaining the filter load from the selected signal is used, the present invention is complicated. This has the effect of suppressing even unnecessary signals having a special spectrum. Furthermore, by applying an algorithm that makes the load of the adaptive filter time-invariant for each range bin, there is an effect that loss in integration processing for target detection is reduced and target signal detection performance is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a radar device according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram of an unnecessary signal suppressing unit according to the first embodiment.

FIG. 3 is a block diagram showing an internal configuration of an adaptive load adjustment range bin selection unit according to the first embodiment.

FIG. 4 is a diagram illustrating a relationship between a range bin to be processed and a range bin for load adjustment according to the first embodiment;

FIG. 5 is a flowchart illustrating an operation of the adaptive filter according to the first embodiment.

FIG. 6 is a spectrum diagram illustrating an operation of the radar device according to the first embodiment.

FIG. 7 is a configuration diagram of a conventional radar device.

FIG. 8 is a processing block diagram of a conventional unnecessary signal suppressing unit using a notch filter bank.

FIG. 9 is a diagram illustrating the operation of a conventional radar device.

FIG. 10 is a spectrum diagram illustrating the operation of the conventional radar device.

[Description of References] 1 antenna element, 2 transmitter, 3 modulation signal generator,
5 transmitter, 6 antenna element, 7 receiver, 8 A
/ D converter, 9 receiving device, 10 beam forming means, 1
Reference Signs List 1 demodulation means, 12 unnecessary signal suppression means using adaptive filter, 13 target detection means, 14 signal processing device, 18
Adaptive load adjustment range bin selection means, 19 Adaptive load adjustment means.

Claims (2)

[Claims] A transmitting means for radiating a transmitting wave, a receiving means for receiving a reflected wave and converting the reflected wave into a digital baseband signal, and a beam forming means for performing a receiving beam synthesis using the digital baseband signal; In the configuration for performing target detection from the received beam combined signal, an adaptive load adjustment range bin selecting means for selecting a signal for obtaining a load of the adaptive filter from the received beam combined signal, and using the selected signal for adaptive load adjustment And an adaptive load adjusting means for obtaining at least one weight, and an adaptive filter type unnecessary signal suppressing means for extracting a target signal from the received beam composite signal. 2. The adaptive load adjustment range bin selecting means selects a range bin in a predetermined section as a load adjustment range bin except for a range bin to be processed and a range bin on both sides of the range bin to be processed. Radar equipment.