JP2006292597A - Radar signal processor, and cfar processing method used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar signal processor capable of preventing an amplitude value of a test cell from getting low, and capable of evading a target detection rate from getting low, even when a plurality of other target signals, a clutter spread along a time direction, an interference signal or the like exists in the vicinity of a degree coming within an averaged cell, with respect to the test cell. <P>SOLUTION: A CFAR (constant false alarm rate) processor (1) 1 restrains the signal spread along the time direction such as the clutter included in a reception signal. A large signal detector 2 detects the signal exceeding a threshold value TH1 out of the signal-restrained reception signals, and a large signal cell removing device 3 removes the cell of the detected signal from the reception signals. A CFAR processor (2) 4 averages the reception signals from the large signal cell removing device 3, and divides the reception signals before processed by an averaged reception signal. A target detector 5 detects the signal exceeding a threshold value TH2 out of the reception signals from the CFAR processor (2) 4, to be output as a target signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radar signal processing apparatus and a CFAR processing method used therefor, and more particularly, to a radar signal processing apparatus that performs CFAR (Constant False Alarm Rate) processing.

  Conventionally, a radar signal processing apparatus generally employs CFAR processing for clutter suppression (see, for example, Patent Document 1 and Non-Patent Document 1). The clutter signal is a reflected signal from the ground, clouds, etc. and spreads in the time direction, while the target signal of aircraft, ships, etc. does not spread in the time direction. It is used to suppress clutter.

  As shown in FIG. 4, the radar signal processing apparatus that performs this CFAR processing includes a CFAR processor (1) 6 and a target detector 7. The CFAR processor (1) 6 includes an averaging processor 61 that performs an averaging process and a divider 62 that performs a division, and as shown in FIG. 5, a signal spreading in the time direction such as clutter. And is output to the target detector 7. The target detector 7 outputs a signal exceeding a predetermined threshold value TH2 as a target signal.

  A general CFAR processing operation will be described with reference to FIGS. FIG. 3 shows a general CFAR process, and FIG. 5 shows examples of signal waveforms in each conventional configuration. The CFAR process is largely composed of an averaging process and a division process.

  The received signal is a signal obtained by sampling a signal continuous in the time direction at regular intervals, and the time and the distance correspond to each other. Therefore, the received signal can be considered as a signal divided into cells for each predetermined distance. In the averaging process, an average value of amplitude values of signals entering a plurality of cells (average cells) on both sides (or one side) of the test cell in which the signal of interest enters is calculated. In the division process, the amplitude value of the test cell is divided by the average value of the averaging cell.

  When a clutter signal spreading in the time direction enters the test cell, the average value changes according to the size of the clutter, and the amplitude value of the test cell is suppressed to the noise level. By delaying the CFAR process by one cell in the time direction, the clutter signal spreading in the time direction is suppressed.

  On the other hand, when a target signal that has not spread in the time direction is input to the test cell and only noise is present in the averaging cell, the clutter signal remains without being suppressed. However, in the CFAR processing, even if the clutter signal is not spread in the time direction, the average value increases when there are a plurality of signals having a large amplitude value in the averaging cell. The amplitude value decreases.

JP-A-3-248077 "Radar signal processing technology" (Sekine Matsuo, published by the Institute of Electronics, Information and Communication Engineers, published on September 20, 1991, P.96-99, Figure 5.2)

  In the conventional radar signal processing apparatus described above, when another target signal enters the averaging cell of the CFAR circuit (see FIG. 3), the average value in the averaging cell increases compared to the case of only noise [FIG. 5 (2)], because the divider divides the amplitude value of the target signal of the test cell by the increased average value, a plurality of other target signals are close to the test cell so that they enter the averaging cell. If the signal is present (hereinafter referred to as a proximity signal), the amplitude value decreases, and the detection rate of the target signal existing in the test cell decreases (see FIG. 5).

  In addition, in the conventional radar signal processing apparatus, not only the other target signal, but also when the clutter signal or interference signal spreading in the time direction is close, the amplitude value of the test cell is reduced as described above, There is a problem that the target detection rate decreases.

  Therefore, the object of the present invention is to eliminate the above-mentioned problems, and to be close enough to the test cell so that a plurality of other target signals, clutter spreading in the time direction, interference signals, etc. enter the averaging cell. Therefore, it is an object of the present invention to provide a radar signal processing apparatus and a CFAR processing method used therefor that can avoid a decrease in target detection rate without reducing the amplitude value of a test cell.

A radar signal processing device according to the present invention is a radar signal processing device that performs CFAR (Constant False Alarm Rate) processing for suppressing clutter on a received signal,
First CFAR processing means for suppressing a signal spreading in a time direction including the clutter in the received signal;
A large signal detecting means for comparing a received signal output from the first CFAR processing means with a preset first threshold and detecting a signal exceeding the first threshold;
Large signal cell removing means for removing a corresponding cell from the received signal based on cell information of the signal detected by the large signal detecting means;
Second CFAR processing means for dividing the received signal before processing by the averaged signal after averaging the received signal from which the cells have been removed by the large signal cell removing means;
Target detection means for comparing a received signal output from the second CFAR processing means with a preset second threshold value and outputting a signal exceeding the second threshold value as a target signal; .

  A CFAR processing method according to the present invention is a CFAR processing method used in a radar signal processing apparatus that performs CFAR (Constant False Alarm Rate) processing for suppressing clutter on a received signal, wherein the radar signal processing apparatus includes: The first CFAR process for suppressing the signal spreading in the time direction including the clutter in the received signal is compared with the received signal output from the first CFAR process and a preset first threshold value. A large signal detection process for detecting a signal exceeding the first threshold, and a large signal cell removal process for removing a corresponding cell from the received signal based on cell information of the signal detected by the large signal detection process; The received signal from which the cells have been removed in the large signal cell removal process is averaged, and then the averaged signal is received before the process. The second CFAR process for dividing the signal, the received signal output from the second CFAR process and a second threshold value set in advance are compared, and a signal exceeding the second threshold value is used as a target signal. The target detection process to be output is executed.

  That is, the radar signal processing apparatus of the present invention includes a first CFAR (Constant False Alarm Rate) processing unit that suppresses a signal spread in the time direction such as clutter included in a received signal, and a first CFAR processing unit. A large signal detecting means for comparing the received signal output from the signal with a predetermined threshold TH1 to detect cell information of a signal exceeding the threshold TH1, and cell information of a signal exceeding the threshold TH1 detected by the large signal detecting means. A large signal cell removing means for removing the corresponding cell from the received signal based on the received signal and outputting it to the second CFAR processing means; and after averaging the received signal output from the large signal cell removing means A second CFAR processing unit that divides the received signal by the averaged signal, and the division result of the second CFAR processing unit is compared with a predetermined threshold TH2. And a target detecting means for outputting a signal exceeding the value TH2 as the target signal.

  As described above, in the radar signal processing apparatus of the present invention, after the clutter signal spreading in the time direction is suppressed in the first CFAR processing means, the large signal not spreading in the time direction is detected by the large signal detection means. An averaging process is performed on the received signal which is detected at a predetermined threshold TH1 lower than the threshold TH2 in the means and the large signal which has not spread in the time direction based on the detected cell information of the large signal is removed by the large signal cell removing means. It is carried out.

  As a result, in the radar signal processing apparatus of the present invention, it is avoided that the average value in the averaging cell increases compared to the case of only noise. Even if clutter spread in the time direction, interference signals, etc. are close enough to enter the averaging cell, the test cell amplitude value is not reduced and the target detection rate is not lowered. It becomes possible.

  The present invention is configured and operated as described below so that a plurality of other target signals, clutter spread in the time direction, interference signals, and the like are close to the test cell so that they enter the averaging cell. Even if it exists, the effect that the fall of a target detection rate can be avoided, without reducing the amplitude value of a test cell.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a radar signal processing apparatus according to an embodiment of the present invention. In FIG. 1, a radar signal processing apparatus according to an embodiment of the present invention includes a CFAR (Constant False Alarm Rate) processor (1) 1, a large signal detector 2, a large signal cell remover 3, and a CFAR processor ( 2) It is composed of 4 and the target detector 5.

  The CFAR processor (1) 1 includes an averaging processor 11 that performs an averaging process on a received signal, and a divider 12 that divides the received signal before processing by an averaged received signal, and is included in the received signal. Suppresses signals that spread in the time direction, such as clutter. The large signal detector 2 compares the received signal output from the CFAR processor (1) 1 with a predetermined threshold TH1, detects a signal exceeding the threshold TH1, and detects cell information of the signal as a large signal cell remover 3 Output to.

  The large signal cell remover 3 removes the corresponding cell from the received signal based on the cell information of the signal exceeding the threshold value TH1 from the large signal detector 2, and the received signal obtained by removing the corresponding cell is the CFAR processor (2). Output to 4. The CFAR processor (2) 4 performs an averaging process on the reception signal output from the large signal cell remover 3 in the averaging processor 41, and then receives the reception signal before the process is averaged in the divider 42. Divide by the signal and output the division result to the target detector 5. The target detector 5 compares the received signal output from the CFAR processor (2) 4 with a predetermined threshold value TH2, and outputs a signal exceeding the threshold value TH2 as a target signal.

  FIG. 2 is a diagram showing signal waveform examples in each configuration of the radar signal processing apparatus according to one embodiment of the present invention. The operation of the radar signal processing apparatus according to one embodiment of the present invention will be described with reference to FIGS.

  First, a received signal [see FIG. 2 (1)] including a target signal which is a clutter signal continuous in the time direction and a plurality of proximity signals not continuous in the time direction is input to the CFAR processor (1) 1. The averaging processor 11 of the CFAR processor (1) 1 performs an averaging process on the received signal. FIG. 2 (2) shows the waveform after the averaging process in the averaging processor 11, and a large amplitude value appears at the time when the clutter signal and the target signal exist.

  Next, the divider 12 of the CFAR processor (1) 1 divides the received signal by the received signal after the averaging process. As a result, the clutter signal continuous in the time direction is substantially suppressed to the noise level, and the amplitude value of the target signal is reduced [see FIG. 2 (3)]. The signal after division is input to the large signal detector 2.

  The large signal detector 2 compares the input signal with a predetermined threshold TH1 and outputs cell information of the received signal exceeding the threshold TH1 to the large signal cell remover 3. Here, by setting the threshold value TH1 to a value lower than the threshold value TH2 in the target detector 5, which will be described later, as shown in FIG. 2 (4), the target signal having the amplitude value reduced by the averaging process is detected. Is done. This is intended to extract a large signal in which the threshold TH1 is not continuous in the time direction, and not only the target signal but also noise or the like may be detected more than in the case of the threshold TH2. This is because it is not necessary to satisfy the false alarm probability Pfa required for the radar apparatus in this process.

  The large signal cell remover 3 removes the corresponding cell of the received signal based on the cell information of the signal exceeding the threshold value TH1 from the large signal detector 2 [see FIG. 2 (5)], and removes the corresponding cell from the received signal. The removed signal is output to the CFAR processor (2) 4.

  The averaging processor 41 of the CFAR processor (2) 4 performs an averaging process on the received signal input from the large signal cell remover 3. In the averaging process of the CFAR processor (2) 4, the number of cells obtained by subtracting the number of cells removed by the large signal cell remover 3 from the total number of cells to be processed becomes the population parameter during the averaging process. FIG. 2 (6) shows the waveform after the averaging processor, and a large amplitude value appears only during the time when the clutter signal exists.

  The divider 42 of the CFAR processor (2) 4 divides the received signal before processing by the received signal after averaging processing. As a result, the clutter signal continuous in the time direction is suppressed, and only the target signal which is a large signal not continuous in the time direction remains [see FIG. 2 (7)].

  The target detector 5 compares the received signal output from the CFAR processor (2) 4 with the threshold value TH2, and outputs a signal exceeding the threshold value TH2 as a target signal. Here, the threshold value TH2 is set so as to satisfy the detection probability Pd and the false alarm probability Pfa required for the radar apparatus.

  Thus, in the present embodiment, after suppressing the clutter signal that spreads in the time direction in the CFAR processor (1) 1, the large signal that does not spread in the time direction in the large signal detector 2 is converted into the threshold value TH2 in the target detector 5. An average process is performed on the received signal, which is detected by a predetermined threshold TH1 lower than the received signal, and the large signal not spread in the time direction by the detected large signal cell information is removed by the large signal cell remover 3.

  Thus, in this embodiment, since the average value in the averaging cell is prevented from increasing as compared with the case of only noise, in the CFAR process, a plurality of other target signals in the time direction are applied to the test cell. Even when spread clutter, interference signals, etc. are close enough to enter the averaging cell, it is possible to avoid a decrease in target detection rate without reducing the amplitude value of the test cell.

It is a block diagram which shows the structure of the radar signal processing apparatus by one Example of this invention. It is a figure which shows the signal waveform example in each structure of the radar signal processing apparatus by one Example of this invention. It is a figure for demonstrating a general CFAR process. It is a block diagram which shows the structure of the radar signal processing apparatus by a prior art example. It is a figure which shows the signal waveform example in each structure of the radar signal processing apparatus by a prior art example.

Explanation of symbols

1 CFAR processor (1)
2 Large signal detector
3 Large signal cell remover
4 CFAR processor (2)
5 Target detector 11, 41 Averaging processor 12, 42 Divider

Claims (8)

A radar signal processing apparatus that performs CFAR (Constant False Alarm Rate) processing for suppressing clutter on a received signal,
First CFAR processing means for suppressing a signal spreading in a time direction including the clutter in the received signal;
A large signal detecting means for comparing a received signal output from the first CFAR processing means with a preset first threshold and detecting a signal exceeding the first threshold;
Large signal cell removing means for removing a corresponding cell from the received signal based on cell information of the signal detected by the large signal detecting means;
Second CFAR processing means for dividing the received signal before processing by the averaged signal after averaging the received signal from which the cells have been removed by the large signal cell removing means;
And a target detecting means for comparing the received signal output from the second CFAR processing means with a preset second threshold value and outputting a signal exceeding the second threshold value as a target signal. A characteristic radar signal processing apparatus.   The radar signal processing apparatus according to claim 1, wherein the first threshold value is set to a value lower than the second threshold value.   3. The radar signal processing apparatus according to claim 2, wherein the second threshold value is set so as to satisfy a detection probability and a false alarm probability required for the radar apparatus.   The second CFAR processing means performs an averaging process using as a parameter the number of cells obtained by subtracting the number of cells removed by the large signal cell removal means from the total number of cells processed by the own apparatus. The radar signal processing apparatus according to any one of claims 1 to 3.   A CFAR processing method used in a radar signal processing device that performs CFAR (Constant False Alarm Rate) processing for suppressing clutter on a received signal, wherein the radar signal processing device includes the clutter in the received signal. The first CFAR process for suppressing the signal spreading in the time direction, the received signal output from the first CFAR process, and a preset first threshold value are compared, and the first threshold value is exceeded. A large signal detection process for detecting a signal, a large signal cell removal process for removing a corresponding cell from the received signal based on cell information of the signal detected in the large signal detection process, and a large signal cell removal process. A second CFAR process is performed in which the received signal from which the cells have been removed is averaged, and the received signal before processing is divided by the averaged signal. And a target detection process of comparing the received signal output from the second CFAR process with a preset second threshold value and outputting a signal exceeding the second threshold value as a target signal. And a CFAR processing method.   6. The CFAR processing method according to claim 5, wherein the first threshold value is set to a lower value than the second threshold value.   7. The CFAR processing method according to claim 6, wherein the second threshold value is set so as to satisfy a detection probability and a false alarm probability required for the radar apparatus.   The second CFAR processing means performs an averaging process using as a parameter the number of cells obtained by subtracting the number of cells removed by the large signal cell removal means from the total number of cells processed by the own apparatus. The CFAR processing method according to claim 5.

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