CN111142097A - A Target Direction Estimation Method in AM Broadcast External Radiator Radar - Google Patents
A Target Direction Estimation Method in AM Broadcast External Radiator Radar Download PDFInfo
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- CN111142097A CN111142097A CN201910606032.9A CN201910606032A CN111142097A CN 111142097 A CN111142097 A CN 111142097A CN 201910606032 A CN201910606032 A CN 201910606032A CN 111142097 A CN111142097 A CN 111142097A
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- 230000005855 radiation Effects 0.000 claims abstract description 19
- 238000005070 sampling Methods 0.000 claims description 13
- 239000011159 matrix material Substances 0.000 claims description 7
- 238000005516 engineering process Methods 0.000 claims description 5
- 238000004364 calculation method Methods 0.000 claims description 4
- 230000003044 adaptive effect Effects 0.000 claims description 3
- 238000005314 correlation function Methods 0.000 claims 2
- 230000002708 enhancing effect Effects 0.000 abstract description 2
- 238000011084 recovery Methods 0.000 description 4
- 230000007547 defect Effects 0.000 description 2
- 238000007476 Maximum Likelihood Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000003491 array Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000021615 conjugation Effects 0.000 description 1
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- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
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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
- G01S13/50—Systems of measurement based on relative movement of target
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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
- G01S7/418—Theoretical aspects
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Abstract
本发明公开了一种调幅广播外辐射源雷达中的目标方向估计方法，包括：确定直达波信号与每一天线接收信号的互模糊函数；基于所述模糊函数，根据待确定回波信号的时延及对应的多普勒频移，获得与所述回波信号对应的虚拟阵列信号；根据所述虚拟阵列信号，获取所述回波信号的波达方向。该方法基于模糊函数的性质，根据待确定回波信号的延迟及对应的多普勒频移，获得与原回波信号对应的虚拟阵列信号，从而增强回波信号的信噪比和信干比，构建显著提升期望回波信号信噪比和信干比的虚拟阵列信号，使得估计极低信噪比回波信号的方向更为准确。
The invention discloses a method for estimating target direction in an AM broadcasting external radiation source radar, comprising: determining a mutual ambiguity function between a direct wave signal and a signal received by each antenna; Extending the corresponding Doppler frequency shift, a virtual array signal corresponding to the echo signal is obtained; according to the virtual array signal, the direction of arrival of the echo signal is obtained. The method is based on the properties of the fuzzy function, and according to the delay of the echo signal to be determined and the corresponding Doppler frequency shift, the virtual array signal corresponding to the original echo signal is obtained, thereby enhancing the signal-to-noise ratio and the signal-to-interference ratio of the echo signal, A virtual array signal is constructed that significantly improves the signal-to-noise ratio and signal-to-interference ratio of the desired echo signal, making it more accurate to estimate the direction of the echo signal with a very low signal-to-noise ratio.
Description
Technical Field
The invention belongs to the field of wireless signal positioning, and particularly relates to a target direction estimation method in an amplitude modulation broadcast external radiation source radar.
Background
An external radiation source radar system detects and tracks targets by processing signals from non-cooperative sources. It is difficult to measure the Direction-of-Arrival (DOA) of the echo signals because the Signal-to-Noise Ratio (SNR) of the echo signals is usually very low and there is strong direct Signal interference.
Most external radiation source radar systems use time differences and doppler frequency shifts to detect objects, which are difficult to obtain for radiation sources with limited bandwidth, such as amplitude modulated radio signals. Therefore, the orientation of the target becomes an important parameter for detecting, tracking, and positioning the target. Currently, phase interferometer technology, Adcock antenna arrays and range-doppler domain array signal processing methods have been used for some external radiation source radar systems. However, these methods have the defects of large system error, serious coupling effect, lack of theoretical analysis and the like, and are difficult to estimate the direction of the echo signal with extremely low signal-to-noise ratio.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a target direction estimation method in an amplitude modulation broadcast external radiation source radar, which can solve the problems of enhancing the signal-to-noise ratio and the signal-to-interference ratio of an echo signal, and can construct a virtual array signal for remarkably improving the signal-to-noise ratio and the signal-to-interference ratio of an expected echo signal, so that the direction of the echo signal with extremely low signal-to-noise ratio is more accurately estimated.
The invention provides a target direction estimation method in an amplitude modulation broadcast external radiation source radar, which comprises the following steps: determining a mutual ambiguity function of the direct wave signal and the received signal of each antenna; based on the fuzzy function, obtaining a virtual array signal corresponding to the echo signal according to the time delay and the corresponding Doppler frequency shift of the echo signal to be determined; and acquiring the arrival direction of the echo signal according to the virtual array signal.
The invention has the following beneficial effects: by calculating the cross-ambiguity function of the direct wave and the array, a virtual array signal is constructed according to the delay of the echo signal to be determined and the corresponding Doppler frequency shift, so that the signal-to-noise ratio and the signal-to-interference ratio of the echo signal are enhanced, and the direction of the echo signal with the extremely low signal-to-noise ratio is more accurately estimated.
Drawings
The invention will be further described with reference to the accompanying drawings and embodiments, in which:
FIG. 1 is a flow chart of an embodiment of the present invention;
FIG. 2 is a two-dimensional time-Doppler plot after conventional processing;
FIG. 3 is a graph of azimuth-Doppler shift in an embodiment of the present invention;
fig. 4 is an elevation-doppler shift diagram in an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a method for estimating a target direction in an am broadcast external radiation source radar, including:
and S10, determining the mutual ambiguity function of the direct wave signal and the received signal of each antenna.
In S10, it is assumed that there are 1 direct wave and L echo signals in the received signal, and the received signal x (k) is composed of the direct signal and its echo signals in the form of time delay and doppler shift, which can be expressed as:
wherein K is a sampling point, and the total number is K; s (k) is a time domain signal; a isi、ηi、τiV and viRespectively the steering vector, amplitude attenuation, time delay and Doppler frequency shift of the ith echo signal;
Fsis the sampling rate; n (k) represents noise; matrices x (k), n (k) and aiIs mx 1, let i-0 denote the direct signal, which corresponds to η0＝1，τ 00 and ν0＝0。
Let the number of antenna elements be M, and the signal received by each antenna be xm(k) And M is 1,2, …, M, performing a beam forming technology on the array signal, and acquiring a direct wave signal as a reference signal: y isR(k)＝wHx (k) s (k), where w is the weight vector of the beamformer. Reference signal yR(k) And the reception signal x of the m-th antennam(k) Is a mutual fuzzy function Fm(τ, ν) is:
where τ represents time shift and ν represents frequency shift, indicates conjugation.
And S20, based on the fuzzy function, obtaining a virtual array signal corresponding to the original echo signal according to the delay of the echo signal to be determined and the corresponding Doppler frequency shift.
In S20, FmThe combination of (τ, v) is expressed as a matrix-form array mutual ambiguity function F (τ, v):
F(τ,ν)＝[F1(τ,ν),F2(τ,ν),...,FM(τ,ν)]T
where T denotes transpose.
F (τ, ν) is an M × 1 dimensional matrix, which can be expressed as:
for an echo signal with i-L, if τL，ν＝νLAnd known yR(k) S (k), then:
wherein tau isLV and vLTime shift and Doppler shift of the L-th echo signal, aLAnd ηLA steering vector and amplitude attenuation representing the lth echo signal.
From this, a virtual array signal corresponding to the original echo signal, i.e. an enhanced virtual echo signal, is obtained.
And S30, acquiring the arrival direction of the echo signal according to the virtual array signal.
According to the virtual array signal, the direction of arrival of the corresponding echo signal to be determined can be obtained by adopting a direction of arrival estimation method, such as a rotation invariant algorithm, a maximum likelihood estimation algorithm and the like.
According to the target direction estimation method in the amplitude modulation broadcast external radiation source radar, the virtual array signal corresponding to the original echo signal is obtained according to the delay of the echo signal to be determined and the corresponding Doppler frequency shift based on the fuzzy function, so that the signal-to-noise ratio and the signal-to-interference ratio of the echo signal are enhanced, the virtual array signal which obviously improves the signal-to-noise ratio and the signal-to-interference ratio of the expected echo signal is constructed, and the direction of the echo signal with the extremely low signal-to-noise ratio is estimated more accurately.
On the basis of the foregoing embodiment, as an alternative embodiment, before S10, the method further includes: and S00, applying a beam forming technology to the direct wave direction, and acquiring the direct wave signal from the received combined signal of the direct wave signal and the echo signal.
According to the above-mentioned combined signal, the direct wave is obtained by applying the beam forming technique to the direction of the direct wave, i.e. the direct signal y in the reference channelR(k) S (k) and echo signals in the monitoring channels
May be obtained by beam forming techniques.
On the basis of the above embodiment, as an alternative embodiment, S30 includes: and according to the virtual array signal, applying a single sampling point MUSIC method to the virtual array signal to obtain the direction of arrival of the echo signal. By the MUSIC method of a single sampling point, more accurate direction of arrival can be obtained.
On the basis of the above embodiment, as an optional embodiment, applying a single sampling point MUSIC method to the virtual array signal, and acquiring the direction of arrival of the echo signal includes: acquiring an array signal of a single sampling point of the virtual array signal, and performing cross-correlation calculation on the array signal of the single sampling point to further obtain a covariance matrix of a recovery rank; and applying an MUSIC method to the covariance matrix of the recovery rank to acquire the direction of arrival of the echo signal.
Specifically, in S30, the array signal of one sampling point is set as:
FL＝[F1(τL,νL),F2(τL,νL),...,FM(τL,νL)]T
the following cross-correlation calculation is made:
wherein FL(m + i) denotes FLThe m + i th element in (b).
The covariance matrix of the recovery rank is:
wherein, KrIs a constant between the number of sources and the number of array elements.
The direction of arrival is estimated using the conventional MUSIC method:
wherein ENIs RFThe superscript H denotes the conjugate transpose, a (θ) is the steering vector:
where d is the array pitch, λ is the wavelength, and θ is the direction of arrival.
According to the target direction estimation method in the amplitude modulation broadcast external radiation source radar, the direction of arrival of the echo signal is obtained through the single sampling point MUSIC method, and the more accurate direction of arrival can be obtained.
On the basis of the foregoing embodiment, as an alternative embodiment, in S10, the applying a beamforming technique to the direct wave direction includes: a robust adaptive beamforming technique is applied to the direct wave direction. By using a robust adaptive beamforming technique, strong interference can be eliminated, making the finally obtained direction of arrival more accurate.
On the basis of the above embodiment, as an alternative, the dimension of the noise subspace is M-2.
Specifically, F (τ)L,νL) There are three signal components: a with guide vectorLWith a steered virtual undesired signal vector aiAnd n (k) virtual noise; the ratio DUR of the amplitude of the virtual desired echo signal to the amplitude of the undesired signal is:
wherein i is 0,1, …, L-1.
The ratio DNR of the amplitude of the virtual desired echo signal to the virtual noise amplitude is:
wherein, PSAnd PNThe power of the direct signal and the noise, respectively.
Since the direct signal is very strong, the direct wave cannot be completely cancelled even if the ratio of the amplitude of the virtual desired echo signal to the amplitude of the virtual undesired signal is very large. In the embodiment of the present invention, the dimension of the noise subspace is set to be M-2, that is, the signal subspace is composed of the desired signal and the residual direct wave.
In a specific application of the invention, a Uniform Circular Array (UCA) of 16 antennas is provided, with the radiation source being more than 1000 kilometers away, so that the transmitted signal reaches the receiving array by ionospheric reflection. The frequency of the source signal is 15.5MHz and the bandwidth <8 kHz.
Setting the receiving array signal as x (k), the processing flow is as follows:
step 1: forming a beam in the direct wave direction to obtain a reference signal: y isR(k)＝wHx(k)≈s(k)。
Step 2: calculating a cross-ambiguity function of the reference signal and the array signal:
and 3, step 3: since the bandwidth of the AM broadcast signal is very narrow, a time difference τ is arbitrarily selectedLAt a Doppler shift of vLForming a single sample point array signal FL＝[F1(τL,νL),F2(τL,νL),...,FM(τL,νL)]T。
And 4, step 4: calculating a covariance matrix of the recovery rank:
And 5, step 5: to RFCarrying out eigenvalue decomposition to obtain a signal subspace EN。
And 6, step 6: computing spatial spectra
Actual time of calculation vLCan be obtained by scanning, and can be combined to obtain a Doppler-DOA image.
The results of the conventional processing of the test data and the results of the inventive processing are shown in FIGS. 2-4. Figure 2 is a time-doppler plot of the combination of data extracted in the doppler dimension from a 2 minute conventional range-doppler plot, from which figure 2 a number of clear target tracks can be seen. And selecting the target at 85 seconds and 18.3Hz for target direction estimation. Since the uniform circular array has two directional dimensions, fixing one of them to scan the other, for example fixing a pitch angle of 65 °, can obtain the degree of the azimuth angle corresponding to the pitch angle. Fig. 3 and 4 are the results of the azimuth and elevation angle estimates of the target at 85 seconds, respectively, where fig. 3 is a doppler-azimuth plot for a fixed elevation angle of 65 ° and fig. 4 is a doppler-elevation plot for a fixed elevation angle of 213 °.
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