CN116224246A - Suppression interference suppression method for joint design of transmitting waveform and receiving filter - Google Patents
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Abstract
The invention discloses a suppression interference suppression method for joint design of a transmitting waveform and a receiving filter, which comprises the steps of establishing a transmitting signal sequence, a receiving signal sequence model and an ASL-based receiving mismatch filter model; constructing a transmit waveform and receive filter joint optimization model considering the dynamic range of the receiver; and solving a joint optimization model by adopting a joint optimization algorithm of the transmitting waveform and the receiving filter to obtain an optimal solution of the transmitting signal and the mismatched filter parameters so as to guide the design of the transmitting signal sequence and the receiving filter. The dynamic range of the combined and optimized transmitting signal and receiving filter can be improved, and the optimized dynamic range can be obtained under different input interference signal ratios.
Description
Technical Field
The invention belongs to the technical field of radar interference, and particularly relates to a suppression interference suppression method for joint design of a transmitting waveform and a receiving filter.
Background
In modern radar systems, pulse compression techniques may utilize specially designed transmit and receive filters to achieve better target detection capability and higher range resolution. The dynamic range of a radar receiver is generally defined as a ratio of the maximum received signal amplitude to the minimum received signal amplitude as an important system design index, which directly affects the performance of multi-target detection. Increasing the dynamic range of the receiver may be achieved by designing a reasonable transmit signal sequence and receive filter.
The problem of jointly optimizing the transmit signal and the receive filter with a priori knowledge of the interference or clutter has been widely studied. Previous studies have focused on optimization of the cross-correlation and cross-ambiguity functions for transmit and receive filters under different doppler conditions. And meanwhile, the SINR/SCNR output by the optimizing filter is used as a measurement criterion, and the receiving filter is optimized. In the convergence process of these algorithms, each iteration needs to solve a convex optimization problem and a hidden convex optimization problem, which increases the complexity of the optimization algorithm. Meanwhile, the radar dynamic receiving range is improved to have an important influence on the target detection performance, and if the radar dynamic receiving range is not considered in the system design, targets are possibly submerged in side lobes of interference or side lobes of the targets are higher than other weak targets, so that the detection capability of the radar is reduced.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a suppression interference suppression method for joint design of a transmitting waveform and a receiving filter aiming at the defects of the prior art.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
a suppression interference suppression method for joint design of a transmitting waveform and a receiving filter comprises the following steps:
s1: establishing a transmitting signal sequence model, a receiving signal sequence model and an ASL-based receiving mismatch filter model;
s2: aiming at the model established in the step S1, constructing a transmitting waveform and receiving filter joint optimization model considering the dynamic range of a receiver;
s3: and solving a joint optimization model by adopting a joint optimization algorithm of the transmitting waveform and the receiving filter to obtain an optimal solution of the transmitting signal and the mismatched filter parameters so as to guide the design of the transmitting signal sequence and the receiving filter.
In order to optimize the technical scheme, the specific measures adopted further comprise:
the above S1 describes a process for establishing a model of a signal sequence to be transmitted and a model of a signal sequence to be received, that is, a model of a signal sequence to be received by superimposing and suppressing discrete point target signals, wherein the process comprises:
the transmitted signal sequence is expressed as s= [ s ] 1 ,s 2 ,...,s N ] T The method comprises the steps of carrying out a first treatment on the surface of the I.e. the transmitted signal is in the form of a phase-keyed signal
The received baseband signal contains a point target signal and a suppressed interference signal, which satisfies the following equation
r=Sx+w
wherein ,representing the transmitted sequence at different distance units, x= [ x ] 0 ,x 1 ,…,x N-1 ,x -(N-1) ,…,x -1 ] T ,x k The scattering coefficients representing different distance units, w, are defined as the interference independent of the target signal, assuming w and { x } k -independent of each other;
the electromagnetic scattering amplitude of the point target is x 0 Average clutter power E [ |x 0 | 2 ]=α 2 ;
The characteristics of the suppression interference use an interference covariance matrix W (1) Represented as wherein ,/>Defined as the average power of the interference, W (1) Is a diagonal element in the interference covariance matrix.
The process for establishing the receiving mismatch filter model based on the minimum mean square error characteristic of ASL in the above step S1 is as follows:
the receive filter employs a mismatch filter with minimum mean square error MSE at the desired distance bin x0The mismatch filter h satisfies h H s=1, then at distance x 0 The mean square error MSE at this point can be expressed as
wherein ,hH Q (s)h and sH Q (h) s represents the average sidelobe level, h H W (1) h represents the interference level after the mismatch filtering process,J k representing a shift matrix with the expression +.>Delta is the unit dirac function;
average sidelobe level ASL and h H s=1 can be expressed as h respectively H Q (s)h and sH Q (h) s, the ASL-based reception mismatch filter can be expressed as:
when h H When s is constant, kappa h H Q (s)h and hH W (1) The maximum of both h may be used to determine the dynamic range of the receive mismatch filter.
The above-mentioned construction process of the joint optimization model of the transmitting waveform and the receiving filter based on the JTRD algorithm in S2 is as follows:
to obtain a larger receiver dynamic range, it is desirable to minimize the average sidelobe level kh H Q (s) h and mismatch filter interference levelh H W (1) And h, enabling the interference level processed by the mismatch filter to be equal to the side lobe level as far as possible, and simultaneously designing the transmitting signal and the mismatch filter to maximally promote the receiving degree of freedom.
JTRD algorithm minimizes the average sidelobe level kh of the mismatch filtered signal H Q (s) h is used as an objective function, and the interference level h of a mismatch filter under a certain signal-to-interference ratio kappa is used H W (1) h. Maximizing the mismatched filtering output of the target signal as a constraint condition, and constructing an optimization model in the following form:
s.t.h H s=1
h H W (1) h=c (κ)
|s n |=1,n=1,2,...,N
wherein ,c(κ) The interference level defined as the mismatch filtering output is related to the preset signal-to-interference ratio kappa; h is a H The s=1 constraint can maximize the mismatch filtered output of the target signal, h H W (1) h suppresses the interference level to a given c (κ) Range at the same time of |s n I=1, n=1, 2.
The above-mentioned S3 combined optimization algorithm of the transmit waveform and the receive filter uses an alternate iterative direction optimization method to decompose the optimization model of the original problem into two sub-problems for alternate iterative optimization, where the two sub-problems are respectively: optimization sub-problem of optimizing filter coefficients when fixing transmit waveformsAnd sub-problem of optimizing the transmit signal when fixing the mismatch filter coefficients +.>
The optimization sub-problem when optimizing the filter coefficients in the fixed transmit waveform is described as
s.t.s H h=1
h H W (1) h=c (κ)
Is a convex optimization problem, because the objective function and the constraint term are both convex problems, the eigenvalue decomposition of the interference covariance matrix can be carried out to obtain +.> wherein ,V(1) Is a feature vector matrix;
v H v=c (κ)
problem pairing using Lagrangian dual methodSolving the problem->Can be expressed as +.>Wherein a and b correspond to the problems +.>Real and complex variables in the constraint, +.>Equivalent to
For a given parameter a and b, one can obtainMinimum solution, denoted->The method is equivalent to solving unconstrained minimisation +.>Lagrangian equation by letting +.>Gradient equal to 0, i.eI.e. by letting +.>Gradient equal to 0, can be obtained +.>Minimum solution, denoted->
problem pairing using the dual methodSolving, the Lagrangian dual equation g (a, b) is defined as the following optimization equation problem
The optimization (Karush-Kuhu-Tucker, KKT) condition of g (a, b) can be expressed as
The dual problem is defined as the problem of maximizing g (a, b) or minimizing-g (a, b);
in order to obtain a maximum g (a, b) relative to b, a g (a, b) gradient equal to 0 can be obtainedThus, +.>Can be carried into g (a, b)The coefficient of the mismatch filter h can be calculated by optimizing the parameters a and b;
the solution of parameter a may be obtained by solving a maximized unconstrained problem ζ (a) using Newton's method or a linear search strategy, and the Lagrangian multiplier a may be based on a given parameterDetermining the corresponding range interval as +.> or
wherein Has characteristic decomposition->Σ is a diagonal matrix, e= [ E ] 1 e 2 …e M ]Is a symmetric matrix, M is a matrix +.>Rank of (c);
maximizing ζ (a) given the transmitted signal sequence s gives the value of a, while the value of b can also be obtained by solving, in which case obtaining optimal parameter values a and b brings the Lagrangian dual function to an optimal value, equivalent to the problemThe optimal value is reached, so that the coefficient of the mismatch filter h can be calculated by optimizing the parameters a and b.
For the fixed mismatch filter coefficients, the problem of optimizing the signal from whomSince it is a non-convex problem, it is difficult to solve, so the re-optimization problem is->For the question->
The sub-problem of optimizing the transmit signal while fixing the mismatched filter coefficients is described as
s.t.h H s=1
|s n |=1,n=1,2,…,N
s.t.h H s=1
Solution optimization by Lagrangian dual methodProblem(s)The Lagrangian function equation for a problem can be expressed as
Wherein c and { d } n Respectively expressed as }The corresponding constraint in the problem is a dual variable, d= [ d ] 1 d 2 ...d N ] T ;
At the same time, the method comprises the steps of,is four times equation, and matrix Q (h) +Diag (d) is a positive definite matrix, the standing point of the Lagrangian function is satisfied +.>So that the following relation s=cq exists between the transmit signal and the mismatch filter (h) +Diag(d)] -1 h。
h(c,{d n })=-c 2 h H [Q (h) +Diag(d)] -1 h+c+c * -1 T d
the purpose is to find the optimal dual variables c and d n The dual function h (c, { d) n }) reaches a maximum value, and thus, the maximization of h (c, { d) n }), in which case the dual variable c=1/h H [Q (h) +Diag(d)] -1 h, the maximized dual optimization problem corresponding to the dual variable d is written as
d and c can be determined by maximizing ζ (d), and the optimized transmit signal s can be calculated by optimizing c, d, and h.
The initial content of the above-mentioned transmit waveform and receive filter joint optimization algorithm includes:
setting an iteration flag k=0, initializing a transmission sequence s (0) Let h be using a random coding sequence (0) =s (0) and v(0) =1。
In an ASL-based transmitting signal and receiving filter joint design algorithm, the optimizing step optimizes the transmitting signal and the mismatched filter coefficient by using an alternate iterative optimization mode;
the alternating optimizing step includes:
first optimizing a mismatch filterBy->Calculation of v (k) At the same time calculate Lagrangian multiplier a (k) Fix s (k) Calculate h (k+1) Alternate optimization of the transmit signal +.>By c=1/h H [Q (h) +Diag(d)] -1 h can obtain c (k) Fix h (k) Calculate s (k+1) 。
The above-described alternately optimized stop conditions are:
judging given iteration stop condition s (k+1) -s (k) ||+||h (k+1) -h (k) ||<∈ 1 Whether or not to meet, where E 1 For the predefined convergence range, if not, repeating the alternative optimization step, and if the iteration stop condition is satisfied, outputting the optimized emission waveform s (k+1) And the optimized adaptive filter coefficient h (k+1) . Namely, in the ASL-based transmitting signal and receiving filter joint design algorithm, the stopping step uses the step length iteration norm as a stopping condition, and when the transmitting signal iteration step length norm and the mismatch filter iteration step length norm are smaller than a set value epsilon 1 And when the algorithm stops optimizing iteration, outputting the transmitting signal parameter and the mismatch filter parameter at the moment.
The invention has the following beneficial effects:
compared with a typical joint optimization algorithm of a transmitting signal and a receiving filter, the method disclosed by the invention has the advantages that the optimization problem is included in the dynamic range of the receiver, and the side lobe level and the interference level after pulse compression are balanced under the premise of simultaneously considering the minimized target scattering coefficient root mean square error (Mean Square Error, MSE) and the dynamic range of the receiver. Meanwhile, for the calculation difficulty brought by the non-convex nature of each optimization sub-problem, a conversion form of the optimization sub-problem is provided to reduce the calculation complexity, the minimum average sidelobe level (Average Sidelobe Level, ASL) is taken as an objective function, the interference level range is restrained, the output of a target signal mismatch filter is maximized as a constraint condition, and for the transmitted signal under the main lobe interference suppression, a transmitting waveform and receiving filter combined optimization algorithm (Joint Transmit Signal and Receiving Filter Design, JTRD) based on the average sidelobe level (Average Sidelobe Level, ASL) is provided, and the JTRD optimization algorithm can simultaneously restrain the interference and the received signal sidelobe level, and improve the dynamic range of the receiver, so that the method is very important for multi-target detection and is particularly suitable for weak target detection under the main lobe interference suppression condition. Compared with a cognitive receiving filter and waveform design (Cognitive Receiver and Waveform, CREW) algorithm, the JTRD-ASL optimization algorithm improves the dynamic range after the combined optimization of the transmitting signal and the receiving filter by 22dB and 12dB respectively, and obtains the optimized dynamic range under different input Interference Signal Ratios (ISR).
Drawings
FIG. 1 is a schematic diagram of an ASL-based receive mismatch filter output dynamic range in an embodiment;
FIG. 2 is a diagram of Frank sequence mismatch filtering output in an embodiment;
FIG. 3 is a CREW sequence mismatch filtered output graph in an embodiment;
FIG. 4 is a graph of the output of a JTRD-ASL algorithm optimizing transmit signal and receive filter mismatch filtering in an embodiment;
FIG. 5 is a graph showing convergence of JTRD-ASL algorithm in an embodiment;
FIG. 6 is a plot of mismatch filtered outputs of an un-optimized transmit signal and an interfering signal at different ISRs in an embodiment;
FIG. 7 is a graph showing the mismatch filtered output of the optimized transmit and interference signals as a function of ISR in an embodiment;
FIG. 8 is a Frank sequence mismatch filtered output map for a multi-objective scenario in an embodiment;
FIG. 9 is a graph of CREW sequence mismatch filtering output for a multi-objective scenario in an embodiment;
FIG. 10 is a graph of the JTRD-ASL optimized mismatch filtered output for a multi-objective scenario in an embodiment;
FIG. 11 is a flow chart of the method of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Although the steps of the present invention are arranged by reference numerals, the order of the steps is not limited, and the relative order of the steps may be adjusted unless the order of the steps is explicitly stated or the execution of a step requires other steps as a basis. It is to be understood that the term "and/or" as used herein relates to and encompasses any and all possible combinations of one or more of the associated listed items.
As shown in fig. 11, a method for suppressing interference and optimizing the joint design of a transmit waveform and a receive filter includes:
s1: establishing a transmitting signal sequence model, a receiving signal sequence model and an ASL-based receiving mismatch filter model; the method comprises the steps of constructing a discrete point target signal superposition suppression interference receiving signal model, and constructing a mismatch filter model based on minimum mean square error (ASL) characteristics;
s2: aiming at the model established in the step S1, constructing a transmitting waveform and receiving filter joint optimization model considering the dynamic range of a receiver;
s3: and solving a joint optimization model by adopting a joint optimization algorithm of the transmitting waveform and the receiving filter to obtain an optimal solution of the transmitting signal and the mismatched filter parameters so as to guide the design of the transmitting signal sequence and the receiving filter.
This step decomposes into two sub-problems of transmit signal design and receive filter design using an alternating direction method based on a mismatch filter model based on minimum mean square error characteristics of the Average Sidelobe Level (ASL). By taking Average Sidelobe Level (ASL) reduction as an evaluation index, a JTRD optimization method based on ASL criteria and Lagrangian dual method is provided aiming at two sub-problems of transmitting signal design and receiving filter design. And solving the transmission optimized waveform and the mismatch optimized filter by a transmission waveform and reception filter joint waveform design (JTRD) optimization method to obtain an optimal solution of the parameters of the transmission signal and the mismatch filter.
In the embodiment, in step S1, a mismatch filter model of the discrete point target signal superposition suppression interference receiving signal model and the minimum mean square error characteristic based on ASL is constructed as follows:
the transmitted sequence is expressed as s= [ s ] 1 ,s 2 ,…,s N ] T I.e. the transmitted signal is in the form of a phase-keyed signal
Assuming that the received baseband signal contains a point target signal and a suppressed interference signal, the receiver acceptance signal is modeled as r=sx+w, where,
wherein, the S matrix stores the transmitted signal models at different distances, x k The scattering coefficients representing the different distance elements, w, are defined as the interference independent of the target signal.
Let w and { x } k And are independent of each other. If the electromagnetic scattering amplitude of a point target is x 0 Then the scattering power of the target at the point is E [ |x 0 | 2 ]=α 2 The interference can be characterized by an interference covariance matrix W (1) Represented as wherein ,/>Defined as the average power of the interference, W (1) Is a diagonal element in the interference covariance matrix.
At a desired distance unit x 0 A mismatch filter with minimum mean square error is adopted, and the mismatch filter h satisfies h for maximizing filtering output H s=1, at distance x 0 The mean square error MSE at this point can be modeled as
wherein ,hH Q (s)h and sH Q (h) s represents the average sidelobe level, h H W (1) h represents the interference level after the mismatch filtering process,
Taking into account h H Q (s)h and sH Q (h) s represents the average sidelobe level ASL and the maximized filter output constraint h, respectively H s=1, the ASL-based reception mismatch filter can be defined as
wherein ,is Signal-to-interference Ratio (SIR). When h H When s is constant, kappa h H Q (s)h and hH W (1) The maximum of both h can be used to determine the dynamic range of the receive mismatch filter, and fig. 1 presents a schematic diagram of the output dynamic range of the ASL-based receive mismatch filter.
In a more specific implementation, in order to minimize the average sidelobe level kh H Q (s) h and mismatch filter interference level h H W (1) And h, enabling the interference level processed by the mismatch filter to be equal to the side lobe level as far as possible, and simultaneously designing the transmitting signal and the mismatch filter to maximally promote the receiving degree of freedom. The optimization problem can be written in the following compact form
s.t.h H s=1
h H W (1) h=c (κ)
|s n |=1,n=1,2,...,N
wherein ,c(κ) The interference level, defined as the mismatch filtered output, is related to a predetermined signal-to-interference ratio k. Problem(s)Is intended to minimize the mismatch filtered signal sidelobe levels. And given h H The s=1 constraint can maximize the mismatch filtered output of the target signal, h H W (1) h suppresses the interference level to a given c (κ) Range at the same time of |s n I=1, n=1, 2.
In the embodiment, the decomposition and optimization problem using the alternate direction method in step S2 is two sub-problem processes of transmit signal design and receive filter design as follows:
optimizing the mismatched filter coefficients when fixing the transmitted signal according to the concept of the alternating direction method can result in sub-problemsOptimizing the transmitted signal while fixing the mismatched filter coefficients gives the sub-problem +.>
s.t.s H h=1 s.t.h H s=1
h H W (1) h=c (κ) |s n |=1,n=1,2,...,N
In an embodiment, the problem of optimizing the mismatched filter coefficients for a fixed transmit signalTo reduce the operation complexity, eigenvalue decomposition of the interference covariance matrix can be obtained +.> wherein ,V(1) Is a feature vector matrix;
v H v=c (κ)
in a more specific implementation, in step S3, with reduced Average Sidelobe Level (ASL) as an evaluation index, a JTRD optimization method based on an ASL criterion and a lagrangian dual method is proposed for two sub-problems of transmit signal design and receive filter design, as follows:
Real and complex variables in the constraint.
In an embodiment, a Lagrangian function may be writtenThe dual function g (a, b) of (a) is defined as follows
The first order optimality condition (Karush-Kuhu-Tucker, KKT) of the dual function g (a, b) is
The dual problem is thus defined as the problem of maximizing g (a, b), parameter a being set so as to obtain the maximized g (a, b) of parameter b, the gradient of g (a, b) over parameter b being equal to0 can be obtainedThereby can be obtained
So when the parameter b and the parameter a satisfy the relation of the above formula, the dual equation g (a, b) can be written as a formula containing only the parameter a
In an embodiment, where a back tracking linear search method is used to find the maximum parameter a, a method based on Armijo Goldstein condition search may be used to search for the maximum in a given direction. The algorithm design starts with a relatively large step size estimate that moves in the search direction and iteratively reduces the step size (i.e., "back-tracking") until the objective function value calculated from the gradient value of the objective function becomes smaller.
In an embodiment, the lagrangian multiplier a may be solved by the following method. Order theWherein Σ is a diagonal matrix, e= [ E ] 1 e 2 …e M ]Is a symmetrical matrix lambda i and ei Respectively is a matrix->Is described, and feature vectors. M is matrix->Rank of (2) may give lambda 1 ≥λ 2 ≥…≥λ M ,/>Order the
Can obtain
I.e. the
thus, the Lagrangian multiplier a is a positive integer and is not equal to 0, with the following relationship
The lagrangian multiplier a can be based on given parametersDetermining the corresponding range interval as +.>Or->
wherein Has characteristic decomposition->Σ is a diagonal matrix, e= [ E ] 1 e 2 …e M ]Is a symmetric matrix, M is a matrix +.>Rank of (c);
in an embodiment, maximizing ζ (a) given the transmitted signal s yields the value of parameter a, while also yielding parameter b based on the relationship between parameter b and parameter a, by optimizing the dual problem g (a, b), the Lagrange problemAnd the optimal solution of the filter h is obtained, so that the coefficient of the optimized mismatch filter h is obtained.
In an embodiment, the problem of optimizing the transmitted signal when the mismatched filter coefficients are fixedIn order to accelerate the solving of the problem, the problem is rewritten +.>For the question->
s.t.h H s=1
In an embodiment, the problem is solved using the Lagrangian dual methodSolving the problem->The Lagrangian equation form may be expressed as
Wherein c and { d } n Respectively expressed as }The corresponding constraint in the problem is a dual variable, d= [ d ] 1 d 2 ...d N ] T
Is a fourth order polynomial due to matrix Q (h) +Diag (d) is a positive definite matrix, so +.>Is bounded. The transmitted signal sequence s is graded to be equal to 0 to obtain
s=c[Q (h) +Diag(d)] -1 h
The dual function h (c, { d n }) is defined as an optimized result that maximizes the following problem
h(c,{d n })=-c 2 h H [Q (h) +Diag(d)] -1 h+c+c * -1 T d
In an embodiment, the dual variable c and the dual variable { d } n The relation of } is
c=1/h H [Q (h) +Diag(d)] -1 h
So the dual problem h (c, { d) n }) can be written as problem ζ (d)
In an embodiment, the lagrangian multiplier d may be solved by the following method. Order the wherein ,Σh As a diagonal matrix, f= [ F 1 f 2 …f M ]Is a symmetric matrix, eta i and fi Respectively is a matrix Q (h) Is described, and feature vectors. M is a matrix Q (h) Rank of (1), may be given η 1 ≥η 2 ≥…≥η M . Let->
recording device
Can obtain
and
Finally, the following relationship can be obtained
So according to given parametersThe lagrangian multiplier d should be located +.>Or->Between, wherein->
In an embodiment, maximizing ζ (d) given a mismatch filter coefficient h yields a value of a dual variable d, while based on a dual variable c and a dual variable { d } n The relation of the two can obtain a dual variable c by optimizing the dual problem h (c,{d n }) may beTo get Lagrangian problemAnd thus an optimized transmit signal s.
In a more specific implementation, the process of solving the transmit optimized waveform and the mismatch optimized filter by the transmit waveform and receive filter joint waveform design (JTRD) optimization method in step S4 to obtain the optimal solution of the transmit signal and the mismatch filter parameters is divided into an initial step, an iterative step and a stop step.
An initial step of an ASL-based transmit signal and receive filter joint design algorithm sets an iteration count index k=0 while initializing the transmit signal to s using a random phase encoded signal (0) Let the receiving filter coefficient h (0) =s (0) and v(0) =1. Simultaneously, the signal-to-interference ratio kappa is set, and the interference level c of mismatched filtering output is set (κ) . Initializing Lagrangian multiplier a (0) ,d (0) 。
The iterative steps of the ASL-based transmitting signal and receiving filter joint design algorithm are as follows: optimizing mismatch filtersLagrangian multiplier a (k) According to the relation
Calculation b (k) By means ofCalculation of v (k) Fix the transmitted signal s (k) Calculating a mismatch filter coefficient h (k+1) 。
Thereafter optimizing the transmitted signalOpposite Lagrangian multiplier d (k) According to the relation
c=1/h H [Q (h) +Diag(d)] -1 h
Calculation c (k) Fix the mismatch filter coefficient h (k) Calculating the transmitted signal s (k+1) 。
The stop step of the ASL-based transmitting signal and receiving filter joint design algorithm is as follows:
judging whether the optimized coefficient meets the step length stopping condition, namely the step length s (k+1) -s (k) ||+||h (k+1) -h (k) ||<∈ 1 Wherein, E1 is a preset stop step. When the iteration step norm meets the stop condition, stopping the iteration and simultaneously outputting the optimized transmission signal s (k+1) And optimized mismatch filter h (k+1) If the iteration stop condition is not satisfied, k=k+1, and the steps of the iteration step are repeated at the same time.
Simulation experiment:
in order to ensure the consistency of experimental results, noise frequency modulation interference in the suppression type interference is used, and the corresponding mathematical expression isThe instantaneous frequency f (t) of the noise-modulated disturbance w (t) is f (t) =f 0 +k fm n(t)。
Assuming n (t) is band-limited white noise, the interference spectrum can be expressed by the following equation
Let the frequency modulation factor be defined as m f =k fm δ/B n > 1, when m f When > 1, the spectral shape approximates a Gaussian distribution, and the interference bandwidth can be written asAssuming a spectrum determination, the cross-correlation coefficient and covariance matrix are fixed.
Let the carrier frequency be f 0 =9.4 GHz, the transmit sequence contains n=100 rectangular sub-pulses, perThe time width of the sub-pulse is t p =100 ns. For noisy fm interferers, the interferer bandwidth is set to 2.5MHz.
Using average sidelobe levels, which may be defined as asl=10log, to scale the transmit signal and interference signal joint optimization receive filter output results 10 h H κQ (s) h (dB). And meanwhile, comparing the mismatch filtering output of the optimized transmitting signal with the mismatch filtering output of the Frank sequence and the CREW sequence.
The autocorrelation function of the Frank sequence as shown in fig. 2 has lower side lobe levels, and the ASL response results in about-37 dB. When the Interference-to-Signal Ratio (ISR) is 10dB, the output result of the Interference Signal after the mismatch filter processing is about-10 dB. This greatly limits the dynamic range of the receive filter output.
Fig. 3 shows the output of a mismatched filter after the joint optimization of the transmit waveform and the receive filter by a cognitive receive filter and waveform design (Cognitive Receiver and Waveform, brew) algorithm. ASL of the mismatch filter output is suppressed to around-34 dB. However, the interfering signal output by the mismatch filter is suppressed to-18 dB.
Fig. 4 shows the result of a mismatched filter output for joint optimization of transmit waveforms and receive filters using the JTRD-ASL optimization algorithm. The mismatch filter output ASL and the interfering signal are suppressed at-30 dB simultaneously. The dynamic range of the combined optimization of the transmit signal and the receive filter is improved by 22dB and 12dB, respectively, in contrast to Frank code and brew sequences.
Fig. 5 shows an output level curve of the disturbance, with the ordinate representing the mismatch filter outputs ASL and is (k+1) -s (k) ||+||h (k+1) -h (k) The abscissa is the number of iterations. From the graph, the algorithm converges after about 8 iterations of optimization.
Fig. 6 shows the mismatch filtered output of the pre-optimized transmit signal and the interference signal along with the ISR change, and fig. 7 shows the mismatch filtered output of the post-optimized transmit signal and the interference signal along with the ISR change. Fig. 6 and 7 depict the output range of the mismatch filter, the transmitted signal and the interfering signal compared to the input ISR. The input ISR range is defined as 0 to 20dB, and the suppression range of the transmitted signal remains unchanged until the output of the mismatch filter is optimized, and the suppression range of the interfering signal decreases as the input ISR increases. However, for a mismatch filter output where the transmit signal and the receive filter are jointly optimized, the degree of suppression of the transmit signal and the interference signal is unchanged and an optimized dynamic range can be obtained at different inputs ISR.
Meanwhile, the simulation laboratory is performed on point targets, and the method provided by the invention is also applicable to multi-target scenes. The multi-objective simulation parameters are as follows, assuming ISR equal to 10dB, the three objectives are divided into units at-40, 0, 20 distances, corresponding amplitudes of-10 dB,0dB and 12dB, respectively.
Fig. 8 shows the result of the Frank encoded mismatch filter output in a multi-object scenario.
Fig. 9 shows the output result of a mismatch filter optimized by the brew algorithm in a multi-target scenario, where two weak targets are submerged in the side lobes of the strong signal and interference, and cannot be detected.
Fig. 10 shows that the output result of the mismatch filter optimized by the JTRD-ASL algorithm in the multi-target scene is marked by circles after the transmission signal and the mismatch filter are optimized, so that the two weak targets can be smoothly detected by the radar receiver, and the signal sidelobes and the interference are obviously reduced after the optimization. Weak targets are effectively detected.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (10)
1. The suppression interference suppression method for the joint design of the transmitting waveform and the receiving filter is characterized by comprising the following steps of:
s1: establishing a transmitting signal sequence model, a receiving signal sequence model and an ASL-based receiving mismatch filter model;
s2: aiming at the model established in the step S1, constructing a transmitting waveform and receiving filter joint optimization model considering the dynamic range of a receiver;
s3: and solving a joint optimization model by adopting a joint optimization algorithm of the transmitting waveform and the receiving filter to obtain an optimal solution of the transmitting signal and the mismatched filter parameters so as to guide the design of the transmitting signal sequence and the receiving filter.
2. The method for suppressing interference according to claim 1, wherein the process of establishing the model of the transmission signal sequence and the reception signal sequence in S1 is as follows:
the transmitted signal sequence is expressed as s= [ s ] 1 ,s 2 ,...,s N ] T ;
The received baseband signal contains a point target signal and a suppressed interference signal, which satisfies the following equation
r=Sx+w
wherein ,representing the transmitted sequence at different distance units, x= [ x ] 0 ,x 1 ,…,x N-1 ,x -(N-1) ,…,x -1 ] T ,x k Scattering coefficients representing different distance units, w being defined as the distance to the targetInterference of signals independent of each other, assuming w and { x } k -independent of each other;
the electromagnetic scattering amplitude of the point target is x 0 Average clutter power E [ |x 0 | 2 ]=α 2 ;
3. The method for suppressing interference according to claim 1, wherein the establishing process of the ASL-based receiving mismatch filter model in S1 is as follows:
the receiving filter uses a mismatch filter with a minimum mean square error MSE, at a desired distance element x 0 Where the mismatch filter h satisfies h H s=1, then at distance x 0 The mean square error MSE at this point is expressed as
wherein ,hH Q (s)h and sH Q (h) s represents the average sidelobe level, h H W (1) h represents the interference level after the mismatch filtering process,J k representing a shift matrix with the expression +.>Delta is the unit dirac function;
average sidelobe level ASL and h H s=1 are denoted as h respectively H Q (s)h and sH Q (h) s, the ASL based receive mismatch filter is expressed as:
when h H When s is constant, kappa h H Q (s)h and hH W (1) The maximum of both h is used to determine the dynamic range of the receive mismatch filter.
4. The method for suppressing interference by joint design of a transmit waveform and a receive filter according to claim 1, wherein the constructing process of the joint optimization model of the transmit waveform and the receive filter in S2 is as follows:
to obtain a larger dynamic range of the receiver, the average sidelobe level kh of the mismatch filtered signal is minimized H Q (s) h is used as an objective function, and the interference level h of a mismatch filter under the signal-to-interference ratio kappa is used H W (1) h. Maximizing the mismatched filtering output of the target signal as a constraint condition, and constructing an optimization model in the following form:
s.t.h H s=1
h H W (1) h=c (κ)
|s n |=1,n=1,2,...,N
wherein ,c(κ) The interference level defined as the mismatch filtering output is related to the preset signal-to-interference ratio kappa; h is a H s=1 constraint maximizes the mismatch filtered output of the target signal, h H W (1) h suppressing the interference level to a given levelC of (2) (κ) Range at the same time of |s n I=1, n=1, 2.
5. The method for suppressing interference by joint design of a transmit waveform and a receive filter according to claim 1, wherein S3 the transmit waveform and receive filter joint optimization algorithm uses an alternative optimization method to decompose an optimization model into two sub-problems for alternative iterative optimization, the two sub-problems are respectively: an optimization sub-problem when optimizing the filter coefficients when fixing the transmit waveform and a sub-problem when optimizing the transmit signal when fixing the mismatched filter coefficients.
6. The method for suppressing interference by joint design of transmit waveform and receive filter as set forth in claim 5, wherein said optimization sub-problem in optimizing filter coefficients while fixing transmit waveform is described as
s.t.s H h=1
h H W (1) h=c (κ)
Is a convex optimization problem, and the eigenvalue decomposition is carried out on the interference covariance matrix to obtain +.>
wherein ,V(1) Is a feature vector matrix;
v H v=c (κ)
problem pairing using Lagrangian dual methodSolving the problem->Expressed in Lagrangian equation form asWherein a and b correspond to the problems +.>Real and complex variables in the constraint, +.>Equivalent to
For a given parameter a and b, we getMinimum solution, denoted->The method is equivalent to solving unconstrained minimisation +.>Lagrangian equation by letting +.>Gradient equal to 0, i.e.)>I.e. by letting +.>Gradient equal to 0, get->The least solution, expressed as
problem pairing using the dual methodSolving, the Lagrangian dual equation g (a, b) is defined as the following optimization equation problem
The optimization conditions of g (a, b) are expressed as
The dual problem is defined as the problem of maximizing g (a, b) or minimizing-g (a, b);
in order to obtain a maximum g (a, b) relative to b, a g (a, b) gradient equal to 0 is obtainedThus, get +.>Can be carried into g (a, b)Calculating the coefficient of the mismatch filter h through optimizing the parameters a and b;
solving the parameter a is obtained by solving a maximized unconstrained problem ζ (a) using Newton's method or a linear search strategy, and the Lagrangian multiplier a is based on a given parameterDetermining the corresponding range interval as +.>Or->
wherein Has characteristic decomposition->Σ is a diagonal matrix, e= [ E ] 1 e 2 …e M ]Is a symmetric matrix, M is a matrix +.>Rank of (c);
maximizing ζ (a) given the transmitted signal sequence s yields a value of a, while b is also obtained by solving, where obtaining optimal parameter values a and b results in an optimal value of the Lagrangian dual function, equivalent to the problemThe optimal value is reached, so the coefficient of the mismatch filter h can be calculated by optimizing the parameters a and b.
7. The method for suppressing interference in a joint design of a transmit waveform and a receive filter according to claim 5, wherein the sub-problem of optimizing the transmit signal while fixing the mismatched filter coefficients is described as
s.t.h H s=1
|s n |=1,n=1,2,...,N
s.t.h H s=1
Solving the optimization problem by Lagrangian dual method The Lagrangian function equation of the problem is expressed as
Wherein c and { d } n Respectively expressed as }The corresponding constraint in the problem is a dual variable, d= [ d ] 1 d 2 …d N ] T ;
d and c are determined by maximizing ζ (d), then the optimized transmit signal s is calculated from the optimized c, d and h.
8. The method for suppressing interference suppression in combination with a transmit waveform and a receive filter according to claim 5, wherein the initial content of the transmit waveform and receive filter combination optimization algorithm comprises:
setting an iteration flag k=0, initializing a transmission sequence s (0) Let h be using a random coding sequence (0) =s (0) and v(0) =1。
9. The method of suppressing interference for a transmit waveform and receive filter joint design of claim 5, wherein said alternately optimizing step comprises:
10. The method for suppressing interference in combination with a transmit waveform and receive filter design of claim 5, wherein the alternate optimization stop condition is:
judging given iteration stop condition s (k+1) -s (k) ||+||h (k+1) -h (k) ||<∈ 1 Whether or not to meet, where E 1 For the predefined convergence range, if not, repeating the alternative optimization step, and if the iteration stop condition is satisfied, outputting the optimized emission waveform s (k+1) And the optimized adaptive filter coefficient h (k+1) 。
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