CN106443595B - A kind of cognition radar waveform design method of anti-instantaneous forwarding slice reconstruct interference - Google Patents
A kind of cognition radar waveform design method of anti-instantaneous forwarding slice reconstruct interference Download PDFInfo
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Abstract
The present invention proposes a kind of cognition radar waveform design method of anti-instantaneous forwarding slice reconstruct interference, the prior information obtained using cognition radar, therefrom extract the relevant parameter of slice reconstruct interference, according to cross-correlation integral sidelobe level minimum criteria between the waveform autocorrelation integral sidelobe level of weighting and the waveform and slice reconstruct interference of weighting, thus the phase code transmitted waveform that can satisfy interference free performance index designed.The present invention is in instantaneous forwarding slice reconstruct interference scene, improve the signal interference ratio near real goal, achieve the purpose that real goal correctly detects, it is good with real-time, the wide advantage of applicability, it can be applied in Radar ECM system, significantly increase ability to work of the radar under novel interference environment.
Description
Technical Field
The invention belongs to the technical field of radar anti-interference, and particularly relates to a radar anti-interference waveform design technology.
Background
New jammers based on Digital Radio Frequency Memory (DRFM) make the radar face interfering signals that are coherent with the transmitted signal.
After intercepting the radar detection signal, the jammer copies, transforms and modulates the radar detection signal to form an interference signal, and then the interference signal is transmitted back to the radar receiver to form novel deception interference which is coherent with the transmitted signal. One of the typical novel spoofing interferences is slice reconstruction interference, see U.S. Patent "m.j.sparrow, j.cakilo.ecm techniques to reciprocal compression radar. united States Patent,7081846,2006-07-25", which affects normal detection of a target by a radar and also consumes radar resources greatly. Especially when jammers can retransmit jammer signals quickly or even instantaneously, radars cannot resist such jammers by simple waveform agility, and such instantaneous retransmission jammers have a very serious influence on normal operation of radars. Therefore, the method has important theoretical value and practical significance for ensuring the correct detection and tracking of the radar to the target under the transient interference environment and improving the capability of the radar to resist the transient forwarding slice reconstruction interference.
The design of radar waveform is an effective measure against the interference of a novel radar based on a digital radio frequency memory DRFM, and various researches on the interference have been made by domestic and foreign research institutions. Soumekh was first concerned with using waveform design techniques to combat DRFM-based copy-fraud interference, see the literature "SAR-ECCM using Phase-conditioned LFM ChirpSignals and DRFM Repeat Jammer Pearlation. IEEE Transactions on Aerospace and electronic System,42(1):191 + 205, 2006". The chirp signal based on phase disturbance and the chirp signal based on frequency modulation disturbance proposed by the document have a good countermeasure effect when the time lag of the interference signal forwarded by the jammer is one or more Pulse Repetition Intervals (PRI) of the radar echo signal. However, when aiming at other types of non-duplicated deception jamming, the anti-jamming performance is poor, and particularly when the delay time of a jamming machine forwarding interference signal relative to a radar echo signal is short, namely under the condition of so-called instantaneous forwarding jamming, the anti-jamming performance is seriously reduced, and a real target may not be correctly detected by a radar. From the published literature at present, the design of radar transmit waveforms for anti-transient forward slice reconstruction interference has not been studied.
Disclosure of Invention
The invention aims to solve the technical problem that a cognitive radar waveform design method is provided for countermeasure aiming at an interference mode which is instantaneous forwarding interference and can be realized based on a DRFM (digital radio frequency modulation) interference machine, and particularly considering novel slice reconstruction interference.
The invention adopts the technical scheme that the cognitive radar waveform design method for resisting instantaneous forwarding slice reconstruction interference comprises the following steps:
a method for designing a cognitive radar waveform resisting instantaneous forwarding slice reconstruction interference is characterized in that a cognitive pulse radar continuously transmits a ray frequency modulation pulse signal and continuously receives an echo signal, and when the fact that a slice reconstruction interference signal is detected in the echo signal is judged, the following steps are carried out:
1) estimating the number m of the interception segments and the replication times l of the slice reconstruction interference signal according to the echo signal;
2) respectively assigning values to the number α of sub-pulses in the slice reconstruction interference pulse and the number p of time slots to be filled in each sub-pulse by using the estimated number m of the intercepted segments and the number l of the copying times to obtain a codeword jam of the slice reconstruction interference signal;
where N denotes the total number of sub-pulses of the phase-encoded signal, phinIs the phase of the nth sub-pulse, phin∈[0,2π]The sub-pulse sequence number variable N is 1,2 … N [ ·]TRepresenting a transpose;
3) calculating an autocorrelation function R (k) of a transmitted waveform from a complex codeword sequence s of the transmitted phase encoded signal; calculating a cross-correlation function R of a transmitting waveform and a slice reconstruction interference waveform according to the complex codeword sequence s and the slice reconstruction interference signal codeword jamsjam(k)；
4) Constructing a cost function lambda, lambda ═ lambda1WISL+λ2WICSL；
Wherein WISL is the weighted integral autocorrelation sidelobe level, WICSL is the weighted integral cross-correlation sidelobe level, lambda1And λ2Weight factors of weighted integral autocorrelation sidelobe level and weighted integral cross-correlation sidelobe level, respectively, and1+λ2＝1；
wherein, w1(k) And w2(k) The weighting vectors of the weighted integral self-correlation side lobe level and the weighted integral cross-correlation side lobe level are respectively used for carrying out dynamic adjustment according to the actually required side lobe suppression range; k is an independent variable, k is-N +1, …,0, …, N-1, and N is the number of sub-pulses of the phase encoding signal;
5) solving the phase parameter vector phi [ phi ] when the cost function lambda is minimized1,φ2,…,φN]For phase parameter vectors of the transmit waveform designed, i.e. satisfied
The phase coding signal used by the cognitive pulse radar is a phase coding emission waveform which can meet the anti-interference performance index and is designed according to the weighted waveform autocorrelation integral sidelobe level and the minimum criterion of the cross correlation integral sidelobe level between the weighted waveform and the slice reconstruction interference by utilizing the prior information acquired by the cognitive radar and extracting the relevant parameters of the slice reconstruction interference from the prior information.
The phase coding waveform designed by the invention has wide application range, can be designed in real time according to related parameters of slice reconstruction interference estimated by a radar in a cognitive process, can dynamically adjust the weighting vector of the integral autocorrelation side lobe level and the weighting vector of the integral cross-correlation side lobe level according to the interested suppression side lobe range, has strong pertinence, and can adjust the weighting factors of the weighted integral autocorrelation side lobe level and the weighted integral cross-correlation side lobe level according to the strength of the interference, so that the radar can still effectively resist the interference under an instant forwarding strong slice reconstruction interference scene, and the effective detection of a real target is realized.
The method has the advantages that in an instantaneous forwarding slice reconstruction interference scene, the signal-to-interference ratio near a real target is improved, the purpose of correct detection of the real target is achieved, the method has the advantages of being good in real-time performance and wide in applicability, can be applied to a radar electronic countermeasure system, and obviously enhances the working capacity of the radar in a novel interference environment.
Drawings
FIG. 1 is a flow chart of the algorithm of the present invention.
Fig. 2 shows the processing result of radar signals under strong interference by using a conventional P3 code waveform.
Fig. 3 is a graph of the autocorrelation of the designed phase encoding waveform and a graph of the cross-correlation of the phase encoding waveform with the slice reconstruction interference waveform.
Fig. 4 shows the radar signal processing results under strong slice reconstruction interference using the designed phase-coded waveform.
Fig. 5 is an iterative convergence curve when designing a phase encoding waveform.
Detailed Description
The invention provides a radar phase coding waveform design method for resisting instantaneous forwarding slice reconstruction interference based on a cognitive pulse radar, which comprises the following steps of:
as shown in fig. 1, a method for designing a radar phase-encoded waveform resistant to transient forward slice reconstruction interference includes the following steps:
step 1: interference detection step
The cognitive pulse radar continuously transmits a chirp signal, continuously receives an echo signal, performs basic analysis on the echo signal, determines whether a slice reconstruction interference signal is detected in the echo signal, continues to perform step 1 if no slice reconstruction interference exists, and returns to step 2 if slice reconstruction interference is detected. The detection of slice reconstruction interference is well-established and will not be described herein.
Step 2: interference parameter estimation step
The cognitive pulse radar carries out real-time analysis on echo signals with slice reconstruction interference signals, and the related parameters of the slice reconstruction interference signals are estimated by using the existing method based on Wigner-Ville transformation and the like: the number of segments m and the number of copies l.
And step 3: constructing a cost function:
the phase-encoded waveform emitted by the radar isOne point per chip, the mathematical expression is as follows:
wherein, tbFor phase-encoding the sub-pulse width, N is the number of sub-pulses, s ═ s1 s2 … sN]TFor complex code word sequences of phase-coded signals, the variable N of the sub-pulse number is 1,2 … N, each element s of the sequence snCode word value representing the point taken for each chip [ ·]TRepresenting transposition, and t represents a current time variable;
code word snThe expression of (a) is:
φnis the phase of the nth sub-pulse of the waveform, phin∈[0,2π]；
The complex envelope u (t) of the sub-pulses is expressed as:
t is the radar transmission pulse width, and T equals Ntb。
For slice reconstruction interference, the received signal of the radar receiving end in the current PRT can be expressed as:
r(t)＝sR(t)+jam(t)+w(t)
wherein s isRAnd (t) is a real target echo signal, jam (t) is a slice reconstruction interference signal which is generated by an interference machine intercepting a radar emission waveform in the current pulse repetition time and according to a generation mode of slice reconstruction interference, and w (t) is a Gaussian white noise signal.
Constructing a slice reconstruction interference signal code word jam by the transmission waveform according to the estimated number m of the segments of the slice reconstruction interference signal and the replication times l and the generation mechanism and the characteristics of reconstruction interference:
wherein α is the number of sub-pulses in the slice reconstruction interference pulse, p is the number of slots to be padded by each sub-pulse, and is equal to the number of slices reconstruction interference parameter truncation segment m and the number of times of copying l, m is α, l is p and has the length of the whole signal code word N is α · p, and since the sequence formed by the code word values corresponding to each sub-pulse is called a complex code word sequence, the number of sub-pulses and the code word length are the same quantity.
The correlation characteristic of the transmitted waveform is determined by the complex codeword sequence s of the waveform, taking into account the autocorrelation function r (k) of the complex codeword sequence s:
wherein k is a sub-pulse sequence number variable, and R (0) is an autocorrelation function peak value; it is readily demonstrated that R (k) ═ R*(-k); denotes conjugation.
Introducing an integrated autocorrelation Sidelobe level isl (integrated Sidelobe level) of a complex codeword sequence s, wherein the expression is as follows:
considering the cross-correlation function of the transmitting waveform and the slice reconstruction interference waveform, namely considering the cross-correlation of the complex codeword sequence s and the slice reconstruction interference codeword sequence jam:
introducing Integrated Cross-correlation side lobe Level (ICSL) between the complex codeword sequence s and the slice reconstruction interference codeword sequence jam, and making
Sometimes, only the side lobes in a certain range near the autocorrelation main lobe are more interested, and in order to further improve the detection probability of the target, only some side lobe levels near the main lobe can be reduced to reduce the influence on the target detection. Considering the weighting processing of the self-correlation side lobe level, a group of weights are designedSome side lobe levels near the main lobe are kept as low as possible. The weighted Integrated autocorrelation sidelobe level wisl (weighted Integrated sidelobe level) of the complex codeword sequence s is:
similarly, considering weighting processing to the cross-correlation side lobe level, a set of weights is designedSome cross-correlation side lobe levels are made as low as possible. When the distance deception jamming is resisted, if the relative time delay between the slice reconstruction jamming and the target is known, the jamming to the target and the distance unit near the target can be reduced by designing the weight, so that the influence of the jamming on target detection is reduced. Defining Weighted Integrated Cross-correlation side lobe Level WICSL (Weighted Integrated Cross-correlation delay Level) as:
wherein, for any k, w1(k)≥0,w2(k)≥0。
In order to improve the detection performance and the slice reconstruction interference resistance of the radar, the waveform design aims to: the weighted integral autocorrelation sidelobe level of the complex codeword sequence s is as small as possible, and the weighted integral cross-correlation sidelobe level between the complex codeword sequence s and the slice reconstruction interference code codeword sequence jam is as small as possible. However, it is difficult to minimize the sidelobe level of the waveform while minimizing the sidelobe level of the waveform, so a compromise cost function needs to be designed:
Λ＝λ1WISL+λ2WICSL
wherein λ is1、λ2Weight factors of weighted integral autocorrelation sidelobe level and weighted integral cross-correlation sidelobe level, respectively, and1+λ21. When the interference energy is large, λ2The value of (a) should be increased appropriately.
In order to suppress slice reconstruction interference, the objective of waveform design is to make the value of the following cost function as small as possible by designing the code words of the phase-encoded waveform set, and then the problem turns into:
wherein phi is [ phi ]1,φ2,…,φN]Is a vector of phase parameters of the transmit waveform.
From the above, constructing a cost function Lambda, firstly assigning a value to the number α of sub-pulses in the slice reconstruction interference pulse and the number p of time slots to be depopulated by each sub-pulse by using the number m of the slice reconstruction interference parameters and the replication times l estimated in the step 2 to obtain a slice reconstruction interference signal codeword jam, and then calculating the cross correlation R of a complex codeword sequence s and a slice reconstruction interference code codeword sequence jamsjam(k) And constructing a cost function lambda according to the weighted integral cross-correlation side lobe level WICSL and the weighted integral self-correlation side lobe level WISL.
And 4, step 4: the cost function simplifies the step, which is to simplify the calculation of step 5.
Step 4-1: simplified integrated autocorrelation sidelobe levels
Defining the autocorrelation matrix of s as:
the autocorrelation function of s is related to this autocorrelation matrix by:
wherein A ism,nRepresenting the mth row and nth column elements of matrix a.
Defining two (N-1) -dimensional column vectors q separatelyrAnd q iscThe expression is as follows:
when the phase parameter of the nth chip in s has a phase increment of delta phi, the chip is updated toBy using the conjugate symmetry of the autocorrelation function, the new autocorrelation function can be simplified as:
wherein q isr(k) And q isc(k) Respectively represent vectors qrAnd q iscThe kth element of (1).
Calculating the square of the autocorrelation function R (k) of the codeword sequence sAnd the euler formula is utilized to expand the real parameters, the real parameters at most contain 5 non-zero real parameters, and the expansion result is as follows:
wherein a is0(k)、a1(k)、a2(k)、a3(k)、a4(k) For simplifying intermediate quantity:
(·)iand (·)rRespectively representing the imaginary and real parts of the element.
Step 4-2: simplified integral cross-correlation side lobe levels
When the radar transmits in a certain PRT, the wave form is s ═ s1,s2,...,sN]TAnd if the slice reconstruction interference waveform is jam ═ jam1,jam2,...,jamN]T＝[s1,…,s1,sp+1,…,sp+1,…,s(α-1)p+1,…,s(α-1)p+1]TWherein N is α. p,andφs(k) and phijam(k) The phase parameters of the k-th chip of the waveform s and jam, k being 1,2, …, N, respectively. Defining a cross-correlation matrix
The elements of the cross-correlation function of the waveforms s and jam are the sums of the elements on the diagonal of the matrix B, i.e.
Wherein, Bm,nRepresenting the mth row and nth column elements of matrix B. The cross-correlation function of the waveforms s and jam satisfies
When the phase parameter of the mth chip in the waveform s has an increment of delta phi, i.e.At this time, the slice reconstruction interference waveform may or may not be changed, which is discussed in the following cases:
1. when m is (n-1) p +1, n is 1,2, …, α, jam has p chips (m to m + p-1 chips) changing in phase simultaneously, and the chips all have delta phi
The mth chip in the waveform s is updated toAt this time, p chips (m to m + p-1 chips) in the waveform jam are updated at the same time, and the chips are updated toOrder to
The new cross-correlation function can be written as:
the mth chip in the calculation waveform s is updated toCross-correlation of post complex codeword sequence s with slice reconstructed interfering codeword sequence jamSquare of the modeAnd the euler formula is utilized to expand the real parameters, the real parameters at most contain 5 non-zero real parameters, and the expansion result is as follows:
wherein b is0(k)、b1(k)、b2(k)、b3(k)、b4(k) For simplifying intermediate quantity:
wherein,(·)iand (·)rRespectively representing the imaginary and real parts of the element.
2. When m ≠ (n-1) p +1, n ≠ 1,2, …, α, no change occurs in chips in jam.
At this point, the new cross-correlation function can be written as:
computingAnd the euler formula is utilized to expand the real parameters, the real parameters at most contain 3 non-zero real parameters, and the expansion result is as follows:
wherein b is0(k)、b1(k)、b2(k) For simplifying intermediate quantity:
step 4-3: simplifying cost functions
Wherein c isi(k) The method is to simplify the intermediate quantity,
ci(k)＝λ1w1(k)ai(k)+(1-λ1)w2(k)bi(k)
i＝0,1,2,3,4 k＝-N+1,…0,…,N-1
and 5: the pattern search algorithm solves the cost function:
step 5-1: initializing the phase parameter phi
The initialization phase may be a random phase, or may be a phase of a common phase-encoded waveform such as a P3 code waveform or a P4 code waveform.
Step 5-2: performing algorithm iterations
Phase parameter phi for the nth phase of the transmit waveformnExpressing the cost function Λ 'as a unary function Λ' [ phi ] of the phase parameter according to the reduction result in the step 4-3n]At this time, the multidimensional optimization problem in the step 3 is converted into a one-dimensional optimization problem:the phase parameter vector Φ is updated using the one-dimensional optimization search results until all phase parameters of the waveform are updated once.
Step 5-3: and stopping iteration, and outputting the designed phase encoding waveform according to the phase parameter vector phi.
Without the simplification of step 4, step 5 directly solves the phase parameter vector phi when the cost function Λ is minimum,
simulation verification and analysis
The effects of the present invention are further explained by the following simulation experiments.
Simulation scene:
the number of transmitting phase coding waveform chips N is 256, the pulse width T is 1 mu s, the pulse repetition period PRT is 10 mu s, the number of slice reconstruction interference sub-pulses α is 8, namely the number of the truncation sections is 8, the number of copying times is 32, the target and the interference are respectively positioned at 5 mu s and 5.1 mu s, the input signal-to-noise ratio SNR is 10dB, the number of PS iteration times is 200, and the number of Monte Carlo simulation times is 200.
Weighting some autocorrelation sidelobe areas (the area is called autocorrelation sidelobe suppression area) of the waveform, and the corresponding weight is
P1Is an integer of 1. ltoreq. P1≤N-1
Similarly, weighting is carried out on some cross-correlation side lobe areas (the area is called as cross-correlation side lobe suppression area) of the cross-correlation function of the waveform and slice reconstruction interference, and the corresponding weight is
P2Is an integer of 0 to P2≤N-1
The weighting areas can be adjusted according to actual engineering application and requirements, and only the weighting mode is discussed in the simulation.
Simulation analysis:
fig. 2 shows the radar signal processing result of the conventional P3 code waveform under strong slice reconstruction interference, and the interference-to-signal ratio JSR is 25 dB. It can be seen that when the interference-to-signal ratio is high, i.e., the interference is strong, the slice reconstruction interference forms a high peak after the matched filtering, which affects the radar detection.
FIG. 3 is a graph of the autocorrelation of a designed phase encoded waveform and a graph of the cross-correlation of the phase encoded waveform with a slice reconstruction interference waveform, λ1＝0.8，P1＝40，P2N. It can be seen that the autocorrelation sidelobes and the cross-correlation sidelobes are well suppressed within the interested sidelobe suppression range, and the normalized amplitude is below-30 dB.
Fig. 4 shows the processing result of the radar signal under the condition that the interference-signal ratio JSR is 25dB by using the designed phase coding waveform, and it can be seen that when the interference-signal ratio is high, i.e. the interference is strong, the slice reconstruction interference is effectively suppressed after being matched and filtered.
Fig. 5 is a convergence curve of the process of designing the phase encoded waveform described above. It can be seen that after the phase parameters are iteratively calculated for 50 times, the value of the cost function tends to converge, the speed is high, and the real-time performance is good.
Claims (3)
1. A method for designing a cognitive radar waveform resisting instantaneous forwarding slice reconstruction interference is characterized in that a cognitive pulse radar continuously transmits a chirp signal at first and continuously receives an echo signal at the same time, and when the slice reconstruction interference signal is detected in the echo signal, the following steps are carried out:
1) estimating the number m of the interception segments and the replication times l of the slice reconstruction interference signal according to the echo signal;
2) respectively assigning values to the number α of sub-pulses in the slice reconstruction interference signal pulse generated according to the phase coding signal and the number p of time slots to be filled in each segment of sub-pulse by using the estimated number m pairs of the intercepted segments and the number l of times of copying to obtain a slice reconstruction interference signal codeword jam;
where N denotes the total number of sub-pulses of the phase-encoded signal, phinIs the phase of the nth sub-pulse, phin∈[0,2π]Number variable N ═ 1,2 … N, [ ·]TRepresenting a transpose;
3) calculating an autocorrelation function R (k) of a transmitted waveform from a complex codeword sequence s of the transmitted phase encoded signal; calculating a cross-correlation function R of a transmitting waveform and a slice reconstruction interference waveform according to the complex codeword sequence s and the slice reconstruction interference signal codeword jamsjam(k)；
4) According to R (k) and Rsjam(k) Constructing a cost function lambda, lambda ═ lambda1WISL+λ2WICSL；
Wherein WISL is the weighted integral autocorrelation sidelobe level, WICSL is the weighted integral cross-correlation sidelobe level, lambda1And λ2Weight factors of weighted integral autocorrelation sidelobe level and weighted integral cross-correlation sidelobe level, respectively, and1+λ2＝1；
wherein, w1(k) And w2(k) Weighting vectors of the weighted integral autocorrelation sidelobe level and the weighted integral cross correlation sidelobe level are respectively, and dynamic adjustment is carried out according to the actually required sidelobe suppression range; k is an independent variable, k is-N +1, …,0, …, N-1, and N is the number of sub-pulses of the phase encoding signal;
5) solving the phase parameter vector phi [ phi ] when the cost function lambda is minimized1,φ2,…,φN]For transmitting phase-encoded signals designed for the vector of phase parameters, i.e. satisfying
2. The method for designing the anti-transient forwarding slice reconstruction interference cognitive radar waveform as claimed in claim 1, wherein the cost function Λ is simplified, and in step 5), the simplified cost function Λ 'is solved, wherein the simplified cost function Λ' is as follows:
where Δ φ represents an increment that satisfies the mth chip s in the complex codeword sequence smHas an increment of delta phi, the chip is updated to exp j (delta phi)]sm；ci(k) Is a reduced intermediate quantity, i is 0,1,2,3,4, ci(k)＝λ1w1(k)ai(k)+λ2w2(k)bi(k)；
Simplified intermediate quantity a0(k)、a1(k)、a2(k)、a3(k)、a4(k)、b0(k)、b1(k)、b2(k)、b3(k)、b4(k) Respectively as follows:
the simplified intermediate quantities x, y, z, x ', y ', z ' are respectively:
simplified intermediate quantity qr、qc、qr(m)、qc(m)Respectively as follows:
wherein s ═ s1 s2 … sN]T，jam＝[jam1,jam2,…,jamN]T，snRepresenting the nth codeword value, jam, of the transmitted phase-encoded waveformnAn nth codeword value representing a slice reconstructed interference signal,*watch conjugation, (.)iAnd (·)rRespectively representing the imaginary and real parts, x, of the elementi、yi、ziIs the imaginary part of the intermediate quantities x, y, z, xr、yr、zrIs the real part of the intermediate quantity x, y, z, xi′、yi′、zi'is the imaginary part of the intermediate quantities x', y ', z', xr′、yr′、zr'is the real part of the intermediate quantities x', y ', z'; q. q.sr(m)(k + N) is an intermediate quantity qr(m)The k + N th element of (1).
3. The method for designing the anti-instantaneous forwarding slice reconstruction interference cognitive radar waveform as claimed in claim 2, wherein the specific method for solving the simplified cost function Λ' by using the pattern search algorithm is as follows:
1) initializing a phase parameter phi;
2) performing algorithm iteration: phase parameter phi for the nth phase of the transmit waveformnThe simplified cost function Λ ' is expressed as a unitary function Λ ' of the phase parameter [ phi ' ]n]Solving forAnd updating the phase parameter vector phi by using the one-dimensional optimization search result, stopping iteration until all phase parameters of the phase encoding signal are updated once, namely N is equal to N, and outputting the designed phase encoding waveform according to the final phase parameter vector phi.
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