CN115508801A - Target detection and identification method based on transmitted waveform matching - Google Patents
Target detection and identification method based on transmitted waveform matching Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
- G01S7/411—Identification of targets based on measurements of radar reflectivity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
Abstract
The invention provides a target detection and identification method based on transmitted waveform matching, which comprises the following steps: s1, transmitting radar signals by using conventional pulse signals and receiving target conventional echo signals; s2, performing time reversal processing on the target conventional echo signal to obtain a time reversal waveform; s3, emitting a time reversal signal by using a time reversal waveform, and receiving a target time reversal echo signal; s4, acquiring a frequency band for enhancing the spectrum energy of the target time reversal echo; s5, distributing the emission energy to the frequency band of the target time reversal echo spectrum energy enhancement to generate a matched emission waveform; s6, synthesizing the matched transmitting waveforms into matched transmitting signals; and S7, performing time-frequency analysis on the target echo to obtain time-frequency data, and extracting target characteristics from the time-frequency data by adopting a classifier to complete target detection and identification. The invention solves the problem of detecting weak targets by a radar system and improves the efficiency of detecting and identifying the targets by the radar.
Description
Technical Field
The invention belongs to the field of target detection of radar systems, and particularly relates to a target detection and identification method based on transmitted waveform matching.
Background
For the detection of a weak target by the existing radar system, the detection power of the radar system for the weak small target is generally improved by means of increasing the transmitting power and increasing the echo accumulation time. For increasing the transmitting power, the conventional radar system usually adopts a phased array system, and the transmitting power of the radar system is increased by increasing the number of transmitting channels and the transmitting power of a single channel and synthesizing high power by using space energy, so that the transmitting power of the radar system is increased, but along with the increase of the transmitting power, the heat consumption of the system is increased sharply, a severe challenge is provided for the heat dissipation design of the radar system, and the system is not suitable for being used by radar systems such as missile-borne radars and the like which are limited by the size of a platform. For increasing the echo accumulation time, under the moving platform, along with the increase of the accumulation time, the distance variation and the speed variation of the target in the accumulation time are increased, so that the problem of distance/speed migration is caused, the power and the detection precision of the radar system are reduced, and the method is not suitable for the detection of the radar system under the high-speed moving platform.
Under a broadband/ultra-wideband radar system, an ultra-wideband signal generally needs to transmit an extremely narrow pulse, and for a radar platform with a limited structural volume, it is difficult to transmit such a pulse, and in order to obtain a long detection distance, the required peak power is often very high, which greatly increases the risk of detection of the radar system; meanwhile, in the ultra-wideband signal, the gain effect of many frequency bands on a radar detection target is not great. Therefore, the frequency band division and frequency optimization can be carried out on the ultra-wideband signals, the frequency band matched with the target characteristics is selected to obtain the optimal echo energy enhancement effect, meanwhile, the time-frequency analysis and characteristic extraction are carried out on the target echo by combining an SPWVD (smooth pseudo-Wigner transform) and other time-frequency analysis method and SVM (support vector machine) and other classifier algorithms, and the detection and identification performance of the radar system on the target can be effectively improved.
At present, the following problems exist in the prior art: 1. only clutter can be suppressed, and the energy of a target echo is improved without gain; 2. the target echo can be matched, detected and identified, but the waveform design work aiming at the target resonance characteristic response is not carried out at the transmitting end, so that the matching degree is poor.
Disclosure of Invention
The invention aims to solve the problem of detection of a weak target by a broadband/ultra-wideband radar system under the condition that the size of a platform is limited. The ultra-wideband radar carries out segmentation on signal frequency bands, selects frequency bands matched with target characteristics, synthesizes working frequency bands to form transmitting waveforms matched with targets, and accordingly obtains the improvement of target echo signal energy. The invention can improve the detection power of the radar system to weak targets under the condition that the radar transmitting power is not improved, and reduce the design difficulty and the engineering realization difficulty of the radar system.
In order to achieve the above object, the present invention provides a method for detecting and identifying a target based on transmit waveform matching, which comprises: step S1, using a conventional pulse signal as a first transmitting waveform, transmitting a radar signal of a first frequency band, and receiving a target conventional echo signal of the first frequency band; s2, performing time reversal processing on the target conventional echo signal of the first frequency band to obtain a time reversal waveform of the first frequency band; s3, taking the time reversal waveform of the first frequency band obtained in the step S2 as a second emission waveform, emitting a time reversal signal of the first frequency band, and receiving a target time reversal echo signal of the first frequency band; step S4, processing the target conventional echo signal of the first frequency band in the step S1 and the target time reversal echo signal in the step S3 to obtain a frequency band of target time reversal echo frequency spectrum energy enhancement; s5, distributing the emission energy to the frequency band of the target time reversal echo spectrum energy enhancement, generating an amplitude modulation waveform matched with the target, and taking the amplitude modulation waveform as a matched emission waveform; s6, synthesizing the matched transmitting waveforms into amplitude modulation matched transmitting signals based on a complex modulation direct digital waveform synthesis frequency synthesizer; and S7, transmitting the matched transmitting signal synthesized in the step S6, receiving an echo signal of the matched transmitting signal to the target, performing time-frequency analysis on the echo signal of the target to obtain time-frequency data of the echo signal of the target, and extracting target characteristics from the time-frequency data by adopting a classifier to complete detection and identification of the target.
Preferably, the performing time-reversal processing on the target conventional echo signal of the first frequency band in step S2 is to perform time-domain inversion and frequency-domain phase conjugation processing on the received target conventional echo signal of the first frequency band to obtain a time-reversal waveform of the first frequency band. Optionally, the step S2 of performing time domain inversion and frequency domain phase conjugation on the received target conventional echo signal in the first frequency band includes the following steps: step S201, transforming a received target conventional echo signal y (t) of a first frequency band from a time domain to a frequency domain by utilizing Fourier transform; step S202, performing phase conjugation transformation on each frequency component; step S203, converting the signal back to a time domain through inverse Fourier transform to obtain a time reversal signal y (-t). .
Preferably, the step S4 of processing the target conventional echo signal of the first frequency band in the step S1 and the target time reversal echo signal in the step S3 to obtain a frequency band with enhanced target time reversal echo spectrum energy includes the following steps: step S401, broadband synthesis is respectively carried out on the target conventional echo signal and the target time reversal echo signal of the first frequency band, and a broadband conventional echo signal and a broadband time reversal echo signal are obtained; step S402, carrying out frequency spectrum processing on the broadband conventional echo signal and the broadband time reversal echo signal; and S403, extracting a frequency band with enhanced time reversal echo spectrum energy according to the spectrum result in the S402.
Preferably, in step S5, no energy is allocated to the frequency band with weakened energy of the time-reversal echo spectrum.
Preferably, the step S5 of generating the amplitude modulation waveform matched with the target is generated based on a direct digital waveform synthesis frequency synthesizer, and the direct digital waveform synthesis frequency synthesizer includes a frequency synthesis unit and an up-conversion module; the frequency synthesis unit provides an external reference input, a reference signal output, local oscillator signals of each stage and ADC/DAC sampling clock signals.
Preferably, the frequency synthesis unit is in communication connection with the up-conversion module, and outputs the reference signal to the up-conversion module, so as to implement primary up-mixing and secondary up-mixing of the output of the reference signal, and form an amplitude modulation waveform matched with a target.
Preferably, the direct digital waveform synthesis frequency synthesizer further includes an AD high-speed sampling module including an ADC unit and a DAC unit, and is configured to implement that the amplitude modulation waveform matched with the target is synthesized into the amplitude modulation matched transmit signal in step S6.
Preferably, in step S7, a SPWVD method is used to perform time-frequency analysis on the target echo matched with the transmit waveform.
Preferably, the time-frequency diagram is preprocessed to improve the image feature extraction capability, and the preprocessing method comprises converting the colored time-frequency diagram into a gray-scale space.
In summary, compared with the prior art, the target detection and identification method based on the transmitted waveform matching provided by the invention has the following beneficial effects:
(1) According to the invention, the transmitting energy is concentrated in the frequency band of the echo energy enhancement after time reversal, and the frequency band of the echo energy without gain does not distribute energy, so that the utilization rate of the transmitting power of the broadband radar is effectively improved;
(2) The complex modulation direct digital waveform synthesis frequency synthesizer based on the high-speed ADC and the DAC is utilized, a matching transmitting signal with amplitude modulation characteristics can be generated, unsaturated distortion-free output of the matching waveform signal is achieved, and maximization of target echo energy gain is guaranteed; meanwhile, the ultra-wideband signals are subjected to frequency band division, a signal frequency band matched with the target resonance characteristics is obtained through processing, and a radar transmitting waveform matched with the target characteristics is synthesized through the frequency band, so that the optimal echo energy enhancing effect is obtained, and the aim of increasing the detection power of a radar system on weak targets is fulfilled;
(3) The method combines the SPWVD and SVM time-frequency analysis method and the classifier, performs time-frequency analysis and image feature extraction on the echo on the basis of target echo energy enhancement, can fully utilize the time-frequency two-dimensional features to identify the target through time-frequency two-dimensional processing, improves the identification probability, and further improves the detection and identification efficiency of the radar on the target.
Drawings
FIG. 1 is a flow chart of a target detection and identification method based on transmit waveform matching according to the present invention;
FIG. 2 is a schematic diagram of a time reversal process according to an embodiment of the present invention;
FIG. 3 is a graph of a conventional echo versus time-reversed echo spectrum comparison for an embodiment of the present invention;
FIG. 4 is a graph of echo spectra after time-reversal echo energy allocation, in accordance with an embodiment of the present invention;
FIG. 5 is a functional block diagram of a direct digital waveform synthesis frequency synthesizer according to an embodiment of the present invention;
FIG. 6 shows an amplitude modulation signal and its envelope output from the frequency synthesizer according to an embodiment of the present invention;
FIG. 7 is a processing result diagram of the SPWVD time-frequency analysis method according to an embodiment of the present invention;
fig. 8 is a diagram of an SVM classification recognition result according to an embodiment of the present invention.
Detailed Description
The technical solution, the structural features, the achieved objects and the effects in the embodiments of the present invention will be described in detail with reference to fig. 1 to 8 in the embodiments of the present invention.
It is to be noted that, in the present invention, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
In this embodiment, a radar system works in a Ku waveband, a target is a typical target, a target angle is 30 °, and based on the conditions of the above embodiments, as shown in fig. 1, the method for detecting and identifying a target based on transmitted waveform matching provided by the present invention includes the following steps:
step S1, using a conventional pulse signal as a first transmitting waveform, transmitting a radar signal of a first frequency band, and receiving a conventional echo signal of a typical target of the first frequency band;
s2, performing time reversal processing on a certain typical target conventional echo signal of a first frequency band to obtain a time reversal waveform of the first frequency band;
s3, taking the time reversal waveform of the first frequency band obtained in the step S2 as a second emission waveform, emitting a time reversal signal of the first frequency band, and receiving a certain typical target time reversal echo signal of the first frequency band;
s4, processing the conventional echo signal of the certain typical target in the first frequency band in the step S1 and the time reversal echo signal of the certain typical target in the step S3 to obtain a frequency band with enhanced frequency spectrum energy of the time reversal echo of the certain typical target;
s5, distributing the emission energy to a frequency band of the time reversal echo spectrum energy enhancement of the certain typical target, generating an amplitude modulation waveform matched with the certain typical target, and taking the amplitude modulation waveform as a matched emission waveform;
s6, synthesizing the matched transmitting waveforms into amplitude modulation matched transmitting signals based on a complex modulation direct digital waveform synthesis frequency synthesizer;
and S7, transmitting the matched transmitting signal synthesized in the step S6, receiving an echo signal of the matched transmitting signal to a typical target, performing time-frequency analysis on the echo signal of the typical target to obtain time-frequency data of the echo signal of the typical target, and extracting characteristics of the typical target from the time-frequency data by adopting a classifier to complete detection and identification of the typical target.
The time reversal processing in step S2 is to perform time reversal operation of the time domain signal by time domain inversion and frequency domain phase conjugation based on a digital signal processing method. As shown in fig. 2, in a preferred embodiment, the time-reversal processing on a typical target conventional echo signal in the first frequency band in step S2 includes the following steps:
step S201, transforming a received certain typical target conventional echo signal y (t) of a first frequency band from a time domain to a frequency domain by utilizing Fourier transform;
step S202, performing phase conjugate transformation on each frequency component, namely performing inverse transformation equivalent to a time domain signal;
step S203, converting the signal back to a time domain through inverse Fourier transform to obtain a time reversal signal y (-t). Specifically, if a typical target conventional echo signal of the received first frequency band is y (t) = s (t) × h (t), the time-reversal waveform of the first frequency band obtained through the time-reversal processing is y (-t) = s (-t) × h (-t).
Wherein, the step S4 of processing the typical target conventional echo signal of the first frequency band in the step S1 and the typical target time reversal echo signal in the step S3 to obtain a frequency band with enhanced spectrum energy of the time reversal echo of the typical target includes the following steps:
step S401, respectively performing broadband synthesis on a certain typical target conventional echo signal and a certain typical target time reversal echo signal of a first frequency band to obtain a broadband conventional echo signal and a broadband time reversal echo signal;
step S402, carrying out frequency spectrum processing on the broadband conventional echo signal and the broadband time reversal echo signal;
and S403, extracting a frequency band with enhanced time reversal echo spectrum energy according to the spectrum result in the S402.
In this embodiment, a typical target normal echo signal and a typical target time reversal echo signal in the first frequency band are processed in steps S401 to S403, and the obtained frequency band with enhanced energy of the time reversal echo spectrum is shown in fig. 3.
Further, the transmission energy is allocated to the frequency band where the energy of the typical target time-reversal echo spectrum is enhanced, as shown in fig. 4, through step S5. And the frequency band with weakened time reversal echo spectrum energy is not distributed with energy. And converting the spectrum signal after energy distribution into an amplitude modulation waveform matched with a certain typical target, and taking the amplitude modulation waveform matched with the certain typical target as a matched transmitting waveform. The processing effect of step S5 is as shown in fig. 4, and the transmission energy is allocated to the frequency band of the time-reversal echo, and the amplitude (solid line in fig. 4) allocated to the frequency band with enhanced energy is greatly increased compared with the amplitude (dotted line in fig. 4) of the original time-reversal frequency band.
Still further, as shown in fig. 5, in this embodiment, the step S5 of generating the amplitude modulation waveform matching a certain typical target is generated based on a Ku-band direct digital waveform synthesis frequency synthesizer, where the Ku-band direct digital waveform synthesis frequency synthesizer includes a frequency synthesis unit 601 and an up-conversion module 602; specifically, the frequency synthesis unit 601 provides an external reference input (the frequency band of the external reference input in this embodiment is 10 to 320 MHz), reference signal outputs (the first reference signal output LO1out =8.2GHz and the second reference signal output LO2out = X1 to X5GHz in this embodiment), local oscillator signals of each stage, and ADC/DAC sampling clock signals; the frequency synthesis unit 601 is communicatively connected to the up-conversion module 602, and outputs the reference signal to the up-conversion module 602, so as to implement primary up-mixing and secondary up-mixing of the reference signal output, and through the processing of the up-conversion module 602, 1.2Ghz is input from the first SMP interface on the right side of the up-conversion module 602, and after sequentially performing mixing processing with the first reference signal output LO1out and the second reference signal output LO2out, the 1.2Ghz intermediate frequency signal is up-converted to an X4 to X8Ghz radio frequency signal, thereby forming an amplitude modulation waveform matched with a certain typical target. In this embodiment, the specific model of the frequency synthesis unit 601 is HQV S _ MW _2G1418SFS, and the specific model of the up-conversion module 602 is HQV S _ MW _2G1418UC.
Meanwhile, the step S6 of synthesizing the matching transmission waveform into the amplitude modulation matching transmission signal is also generated based on a Ku band direct digital waveform synthesis frequency synthesizer, and the core of the generation of the amplitude modulation matching transmission signal is an AD high-speed sampling module (not shown in the figure), which includes an ADC unit and a DAC unit. Specifically, the ADC unit is configured to convert an analog signal into a digital signal, in this embodiment, the ADC unit is designed using ADC12DJ5200RF of TI corporation, so as to implement high-speed sampling and preprocessing with a sampling rate of 9.64GSPS and a 12-bit resolution in a single channel mode; the DAC unit is configured to convert a digital signal into an analog signal, and in this embodiment, the DAC unit employs a DAC38RF82 of ADI corporation to implement I, Q complex modulation at a 2.4GSPS sampling rate in a single channel mode at a 16-bit resolution, so as to copy phase information matching a transmission signal. Specifically, as shown in fig. 6, fig. 6 shows the matched transmitting signal and its envelope (the upper graph of fig. 6 is the envelope) generated through steps S6 to S7.
In this embodiment, in step S7, a SPWVD method (smooth pseudo-wigner transform method) is used to perform time-frequency analysis on a certain typical target echo matching the transmitted waveform. The echo signals are mapped to a time-frequency domain through an SPWVD method, the influence of cross terms is removed while the original time-domain signal information is kept, but a small amount of noise still exists in a time-frequency graph obtained through the SPWVD method, and the extraction of image features is not facilitated. Therefore, the image feature extraction capability needs to be improved by preprocessing the time-frequency image. The pretreatment method comprises the following steps: the color time-frequency graph is converted into a gray-scale space, and then image feature extraction is performed, wherein the effect is shown in fig. 7, and fig. 7 is a time-frequency gray-scale graph of a typical target. Further, in this embodiment, in step S7, an SVM classifier is used to extract a characteristic of a certain typical target from the time data, so as to complete detection and identification of the certain typical target.
In summary, compared with the prior art, the target detection and identification method based on transmitted waveform matching provided by the invention improves the utilization rate of the transmitted power of the broadband radar, realizes the unsaturated undistorted output of the matched waveform signal, and improves the target detection and identification efficiency of the radar.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims (10)
1. A target detection and identification method based on transmitted waveform matching is characterized by comprising the following steps:
step S1, using a conventional pulse signal as a first transmitting waveform, transmitting a radar signal of a first frequency band, and receiving a target conventional echo signal of the first frequency band;
s2, performing time reversal processing on the target conventional echo signal of the first frequency band to obtain a time reversal waveform of the first frequency band;
s3, taking the time reversal waveform of the first frequency band obtained in the step S2 as a second emission waveform, emitting a time reversal signal of the first frequency band, and receiving a target time reversal echo signal of the first frequency band;
s4, processing the target conventional echo signal of the first frequency band in the S1 and the target time reversal echo signal in the S3 to obtain a frequency band with enhanced target time reversal echo frequency spectrum energy;
s5, distributing the emission energy to the frequency band of the target time reversal echo spectrum energy enhancement, generating an amplitude modulation waveform matched with the target, and using the amplitude modulation waveform as a matched emission waveform;
s6, synthesizing the matched transmitting waveforms into amplitude modulation matched transmitting signals based on a complex modulation direct digital waveform synthesis frequency synthesizer;
and S7, transmitting the matched transmitting signal synthesized in the step S6, receiving an echo signal of the matched transmitting signal to the target, performing time-frequency analysis on the echo signal of the target to obtain time-frequency data of the echo signal of the target, and extracting target characteristics from the time-frequency data by adopting a classifier to complete detection and identification of the target.
2. The method for detecting and identifying a target based on transmit waveform matching according to claim 1, wherein the step S2 of performing time reversal processing on the target conventional echo signal of the first frequency band is to perform time domain inversion and frequency domain phase conjugation processing on the received target conventional echo signal of the first frequency band to obtain a time reversal waveform of the first frequency band.
3. The method for detecting and identifying a target based on transmit waveform matching according to claim 2, wherein the step S2 of performing time domain inversion and frequency domain phase conjugation on the received target conventional echo signal in the first frequency band includes the following steps:
step S201, transforming a received target conventional echo signal y (t) of a first frequency band from a time domain to a frequency domain by utilizing Fourier transform;
step S202, performing phase conjugation transformation on each frequency component;
step S203, converting the signal back to a time domain through inverse Fourier transform to obtain a time reversal signal y (-t). .
4. The method for detecting and identifying a target based on transmit waveform matching according to claim 1, wherein the step S4 of processing the target conventional echo signal of the first frequency band in the step S1 and the target time-reversal echo signal in the step S3 to obtain a frequency band with enhanced target time-reversal echo spectrum energy comprises the following steps:
step S401, broadband synthesis is respectively carried out on a target conventional echo signal and a target time reversal echo signal of a first frequency band, and a broadband conventional echo signal and a broadband time reversal echo signal are obtained;
step S402, carrying out frequency spectrum processing on the broadband conventional echo signal and the broadband time reversal echo signal;
and S403, extracting a frequency band with enhanced time reversal echo spectrum energy according to the spectrum result in the S402.
5. The method for detecting and identifying targets based on transmit waveform matching according to claim 1, wherein in step S5, no energy is allocated to the frequency band with weakened energy of the time-reversal echo spectrum.
6. The method for detecting and identifying targets based on transmitted waveform matching according to claim 1, wherein the step S5 of generating the amplitude modulation waveform matched with the targets is based on a direct digital waveform synthesis frequency synthesizer, and the direct digital waveform synthesis frequency synthesizer comprises a frequency synthesis unit (601) and an up-conversion module (602); the frequency synthesis unit (601) provides an external reference input, a reference signal output, local oscillator signals of each stage and ADC/DAC sampling clock signals.
7. The method for detecting and identifying targets based on transmitted waveform matching according to claim 6, wherein the frequency synthesis unit (601) is connected to an up-conversion module (602) in communication, and outputs the reference signal to the up-conversion module (602) for implementing primary up-mixing and secondary up-mixing of the output of the reference signal to form an amplitude modulation waveform matching the target.
8. The method for detecting and identifying targets based on transmitted waveform matching according to claim 7, wherein the direct digital waveform synthesis frequency synthesizer further comprises an AD high-speed sampling module including an ADC unit and a DAC unit, for implementing the step S6 of synthesizing the amplitude modulation waveform matched with the target into the amplitude modulation matched transmitted signal.
9. The method for detecting and identifying targets based on transmit waveform matching as claimed in claim 1, wherein step S7 uses SPWVD to perform time-frequency analysis on the target echoes matching the transmit waveform.
10. The method of claim 9, wherein the pre-processing of the time-frequency diagram is performed to improve image feature extraction capability, and the pre-processing comprises converting the color time-frequency diagram into a gray-scale space.
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