JP2009250616A - Radar signal processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar signal processing device having a simple constitution, capable of improving a target detection probability by suppressing in the low state, a wrong alarm probability caused by a noise, in a pulse Doppler radar device. <P>SOLUTION: This device is equipped with: a reception part for receiving a reflected wave from a target, and outputting a time series of received pulse signals in each distance from the radar device; a signal processing part for applying coherent integration to the time series of the received pulse signals for each distance, and calculating a frequency series of received data in each distance; a signal detection part for applying CFAR processing relative to each frequency component to the frequency series of the received data for each distance, and detecting the frequency series of the received data having an S/N ratio over a detection threshold; and a filter correlating part for determining whether the time series of the received pulse signals is generated by the reflected wave from the target or by a noise, based on the correlation in the frequency direction of the detected frequency series of the received data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radar signal processing apparatus used in a radar apparatus, and more particularly to a pulse Doppler radar system that obtains a Doppler filter component by performing coherent integration processing on a received signal. The present invention relates to a radar signal processing apparatus that can improve the detection probability of N received signals.

  In radar signal processing, a radar signal processing device described in Japanese Patent Laid-Open No. 2001-208835 is known as a conventional device that improves the detection probability of a low S / N reception signal while suppressing the false alarm probability of reception processing. is there.

  In this conventional radar signal processing apparatus, target detection processing is performed by comprehensive judgment of a plurality of signal processes throughout the apparatus. By this comprehensive process, the false alarm probability Pfa can be kept low without reducing the detection probability Pd. Specifically, in this radar signal processing device, in order to increase the target detection probability in the clutter-free region, an “inter-hit amplitude difference test system” and a “CFAR (Constant False Alarm Rate) processing system” 2 signal processing. In any signal processing, the detection threshold is set lower than the detection threshold (threshold value) of the original received signal necessary to obtain the desired false alarm probability Pfa.

  In general, if the radar signal detection threshold is set low, the radar signal detection probability Pd is increased, but the probability of detecting a noise signal is also increased, so that the false alarm probability Pfa is also increased. However, in this conventional apparatus, the false alarm probability Pfa is kept low while keeping the detection probability Pd high by comprehensively processing using the results of the individual signal processing in the above two systems. Is. In other words, the former “hit amplitude difference test system” processes the target signal from the noise signal by paying attention to the signal amplitude difference between hits of the received signal. On the other hand, the processing of the latter “CFAR processing system” performs normal CFAR processing. By taking the logical product (AND operation) of these two signal processing outputs, the detection probability Pd is improved while satisfying the desired false alarm probability Pfa.

  The overall processing of the above two systems of signal processing will be described in more detail. First, in the processing of “CFAR processing system”, the CFAR coefficient of the CFAR circuit is set lower than a value satisfying a desired false alarm probability Pfa. With this setting, the detection probability Pd can be increased. On the other hand, in the process of “amplitude difference test system between hits”, the amplitude within the same coherent pulse interval (hereinafter referred to as “CPI”) of the same range bin is substantially constant in the original radar signal. On the other hand, it is noted that noise signals are scattered in a Rayleigh distribution.

  The detection threshold is set by utilizing the difference in properties between the radar signal and the noise signal. In the processing of the “amplitude difference test system between hits”, for example, the variance of the amplitude between hits is calculated, and if the variance is smaller than a certain value, the output signal is output to the subsequent AND circuit as “detected”. send. The detection threshold set at this time is set to a value lower than usual so that the values of the false alarm probability Pfa and the detection probability Pd are larger. In the AND circuit, when there is a detection output from the above two processing systems, that is, when both are “detection present”, “detection is present”, and the result is output to the subsequent processing device. By the total processing of the two signal processings, only a signal having a large amplitude and a small amplitude variance between hits is output as a received signal. As a result, a desired false alarm probability Pfa is achieved, and the value of the detection probability Pd including detection of a low S / N signal can be increased.

JP 2001-208835 A

  However, since the conventional radar signal processing apparatus described above requires two signal processing systems, that is, an “hit amplitude difference test system” and a “CFAR processing system”, the signal processing apparatus becomes large-scale, There was a problem that it was difficult to reduce costs.

  In addition, as means for increasing the detection probability Pd of a low S / N signal by a method other than the above and further suppressing the false alarm probability Pfa, in principle, “increase transmission pulse power per transmission pulse”, “multiple transmission pulses” Can be mentioned. However, the former means has a problem that the transmission unit becomes large-scaled and the cost of the entire apparatus increases as the power increases. On the other hand, the latter means has a problem in that the data rate is lowered with the increase in the number of transmission pulses, and the implementation of the apparatus is restricted.

  The present invention has been made to solve the above-described problems of the prior art. The present invention has a system for performing normal coherent integration processing and CFAR processing. In this system, the CFAR coefficient of the CFAR circuit is set lower than a value necessary to satisfy the desired false alarm probability Pfa (that is, the detection threshold is lowered), thereby detecting a low S / N signal. The detection probability Pd including is increased. As a result, the false alarm probability Pfa is increased and the false alarms are increased. Accordingly, in order to compensate for the increase in the false alarm probability Pfa, attention is paid to the difference in correlation (continuity) in the frequency domain between the target signal and the noise signal, and the target signal and the noise signal are determined based on the difference in correlation. The false alarm probability Pfa is suppressed by identifying.

  A radar signal processing device according to claim 1 is used in a radar device, and receives a reflected wave from a target and outputs a time series of received pulse signals for each distance from the radar device; A signal processing unit that performs coherent integration on the time series of received pulse signals for each distance to calculate a frequency series of received data for each distance, and CFAR processing for each frequency component for the frequency series of received data for each distance And a signal detector for detecting a frequency sequence of received data having an S / N ratio equal to or higher than a detection threshold, and a time series of the received pulse signal based on the correlation in the frequency direction of the frequency sequence of the detected received data. And a filter correlator for determining whether the target is a reflected wave or noise.

  In the radar signal processing device according to claim 2, in the signal detection unit, the value of the CFAR coefficient in the CFAR process is set lower than the original coefficient value that can obtain the desired false alarm probability Pfa, and the detection threshold is set. By lowering the signal, the detection probability Pd of the radar apparatus is increased by enabling detection of a low S / N signal from the target, and the filter correlator has a correlation between the signal from the target and noise in the frequency direction. The difference between the two is analyzed, the signal from the target and noise are discriminated based on the analysis result, and the false alarm probability Pfa is suppressed.

  Since the radar signal processing apparatus of the present invention has the configuration as described above, in particular, by adopting a combination of normal CFAR processing in the signal detection unit and correlation processing in the filter correlation unit, There is an effect that it is possible to obtain a radar device that does not use a signal processing device, has a low detection cost, and has a low false alarm probability.

Embodiment 1 FIG.
Generally, when a threshold value (threshold value) for signal detection is lowered, a target having a low S / N (a target existing at a long distance from a radar device or a target having a low RCS (Radar Cross Section)) is detected. And detection probability Pd is improved. However, the false alarm probability Pfa due to noise or the like increases at the same time. Here, considering the amplitude distribution of the received signal from the target and noise in the frequency direction, the received signal from the target has a larger amplitude in the adjacent Doppler frequency component than in the Doppler frequency component having a large amplitude. On the other hand, in the case of noise, the amplitude is not always large in the frequency component adjacent to the Doppler frequency component having a large amplitude. Therefore, it is possible to improve the determination accuracy of the received signal and noise from the target by using the difference in the properties, and to suppress the false alarm probability Pfa. The present embodiment utilizes this property.

  FIG. 1 is a schematic block diagram showing the configuration of the radar signal processing apparatus of the present invention. In FIG. 1, 1 is a transmission unit that outputs a transmission pulse signal, 2 is an antenna unit that radiates the transmission pulse signal to space and receives a reflected wave from the target object, and 3 is a reception process for the reflected wave from the target object. It is a receiving part. Reference numeral 4 denotes a signal processing unit that performs coherent integration processing on the received pulse signal sequence to calculate a received data sequence.

  The received pulse signal train is a signal that can be expressed on a two-dimensional coordinate axis of distance and time. If the received pulse signal sequence is classified according to the distance from the radar apparatus, it can be viewed as a time-series set of received pulse signals for each distance. On the other hand, the received data series is a signal that can be expressed on a two-dimensional coordinate axis of distance and frequency. If the received data series is classified according to the distance from the radar apparatus, it can be viewed as a set of frequency series of received data for each distance. As is clear from the above description, the received data sequence can be regarded as a result of subjecting the received pulse signal sequence to a Fourier transform process on a time-series signal for each distance.

  A signal detection unit 5 performs signal detection processing such as CFAR for each frequency component on the reception data sequence calculated by the signal processing unit 4 to detect a signal having an S / N ratio equal to or higher than the detection threshold. Reference numeral 6 refers to the correlation (continuity) on the frequency axis of the received data sequence that has passed through the signal detection unit 5 and is quantized, and whether the signal detected by the signal detection unit 5 is a signal from the target target. A filter correlation unit that determines whether the signal is a noise signal.

  Next, the operation of the radar signal processing apparatus of the present invention having the above configuration will be described. The transmission unit 1 generates and outputs a transmission pulse signal. This transmission pulse signal is radiated as a transmission radio signal from the radar apparatus to the space through the antenna unit 2 via the circulator. The radiated radio wave signal is reflected by the target and returns to the radar apparatus again as a received radio wave signal. This received radio wave signal is received by the antenna unit 2 and input to the receiving unit 3 via the circulator.

  The receiving unit 3 outputs the received radio wave signal to the signal processing unit 4 as a received pulse signal sequence. This received pulse signal sequence is a signal that can be expressed on a two-dimensional coordinate axis of distance and time. The signal processing unit 4 performs coherent integration on the received pulse signal sequence to calculate a received data sequence. This received data series is a signal that can be represented on a two-dimensional coordinate axis of distance and frequency. FIG. 2 shows an example of the received data series. By performing a coherent integration process on the received pulse signal sequence, a received data sequence expressed on the “distance-frequency” axis is converted and generated.

  The signal detection unit 5 performs signal detection processing such as CFAR for each frequency component on the received data series. In the CFAR process, a certain threshold value (detection threshold) corresponding to the S / N ratio of the signal to be processed is set. A signal having an S / N ratio equal to or higher than the detection threshold is detected. FIG. 3 shows a state of the quantized reception data sequence obtained by the CFAR process on the distance versus frequency axis. Here, the setting of the detection threshold in the CFAR process is set lower than the threshold value necessary for obtaining the original false alarm probability Pf. This is because the false alarm probability Pfa can be improved by determining the correlation in the frequency direction of the detection signal by the filter correlation unit 5 in the subsequent stage. It becomes possible to increase the detection probability by including the detection of the low S / N signal by increasing the detection signal by lowering the threshold.

  If the detected signal is continuously detected in the frequency axis direction, the filter correlator 5 determines that the received signal is from the target and “detects”. This continuity in the frequency axis direction is also called correlation. Specifically, it is determined that there is a correlation (continuity) when a signal having a predetermined level or higher exists within a certain frequency range. On the other hand, if the signal is not continuously detected in the frequency axis direction, it is determined as noise (false alarm), and the detected signal is set to “no detection”. The result of filter correlation in FIG. 3 is shown in FIG. In FIG. 4, a signal surrounded by a broken line is detected as a signal from the target. Thereby, it is possible to suppress the false alarm probability Pfa while maintaining the detection probability Pd including the detection of the low S / N signal.

It is a block diagram which shows schematic structure of the radar signal processing apparatus by Embodiment 1 of this invention. It is a figure which shows an example of the received data series after the coherent integration in the signal processing part in the radar signal processing apparatus according to the first embodiment of the present invention. It is a figure which shows an example of the received data series quantized after the CFAR process in the signal detection part in the radar signal processing apparatus according to Embodiment 1 of the present invention. It is a figure which shows an example of the signal from the target detected by the filter correlation in the filter correlation part in the radar signal processing apparatus by Embodiment 1 of this invention.

Explanation of symbols

1 transmitting unit, 2 antenna unit, 3 receiving unit, 4 signal processing unit, 5 signal detecting unit,
6 Filter correlation unit.

Claims (2)

In a radar signal processing device used in a radar device,
A reception unit that receives a reflected wave from the target and outputs a time series of received pulse signals for each distance from the radar device; and
A signal processing unit that performs coherent integration on a time series of received pulse signals for each distance and calculates a frequency series of received data for each distance;
A signal detector for performing a CFAR process for each frequency component on the frequency sequence of the received data for each distance and detecting a frequency sequence of the received data having an S / N ratio equal to or higher than a detection threshold;
A filter correlator that determines whether the time series of the received pulse signal is due to a reflected wave from the target or noise based on the correlation in the frequency direction of the frequency series of the detected reception data. Radar signal processing device. In the signal detection unit, the value of the CFAR coefficient in the CFAR process is set lower than the original coefficient value capable of obtaining the desired false alarm probability Pfa, and the detection threshold is lowered to reduce the low S / N from the target. By enabling signal detection, the detection probability Pd of the radar device is increased,
The filter correlator analyzes the difference in correlation between the signal from the target and the noise in the frequency direction, determines the signal and noise from the target based on the analysis result, and suppresses the false alarm probability Pfa. The radar signal processing apparatus according to claim 1.

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