Disclosure of Invention
Aiming at the defects of the prior art, the technical problem solved by the invention is how to reasonably allocate resources of a multi-target imaging task in a single radar from the perspective of the target direction and the distance direction so as to improve the overall performance of the system.
In order to solve the technical problems, the technical scheme adopted by the invention is a resource self-adaptive scheduling method for inverse synthetic aperture radar two-dimensional sparse imaging, on the basis that radar performs feature cognition on each target, the pulse resource demand of each target is calculated, the sub-pulse transmitting position required to be allocated to each target is further determined according to the constraint condition selected by the radar, and echoes are obtained through alternate observation of the targets, so that the inverse synthetic aperture imaging task of a plurality of targets is completed, and the method comprises the following steps:
the radar transmits a small amount of pulses to each target and estimates the flight parameters of the target, and the specific process is as follows:
the waveform parameters for estimating the target parameters of a small number of pulses transmitted by each target are set as follows: carrier frequency f
rcPulse width T of sub-pulse
rpFrequency step length Δ f
rSub-pulse repetition frequency F
PRFBandwidth B
r. After the radar echo signal is obtained, the distance of the jth target from the radar can be measured by a radar conventional algorithm
Target speed
Target course
Target height
(II) estimating the two-dimensional size of the target, wherein the specific process is as follows:
for radar echo signals, an inverse synthetic aperture radar imaging method in the prior art is adopted to obtain a j-th target coarse resolution inverse synthetic aperture radar image Srj(k, l) normalizing the inverse synthetic aperture radar image using the following equation:
wherein k and l respectively represent the position of the target distance direction and the position direction envelope, and a proper threshold T is set
sCalculating distance to envelope position minimum
And maximum distance to envelope position
According to the relation between the target distance and the envelope position, the distance dimension of the jth target can be obtained
Where ρ is
rr=c/(2B
r) Is the distance resolution; the minimum and maximum values of the position envelope position in the azimuth direction are calculated by the same method respectively
The azimuth dimension of the jth target can be obtained
Wherein
Is the azimuth resolution.
(III) determining the number of target transmission pulse trains and the number of sub-pulse transmissions under the pulse trains by the radar, and the specific process is as follows:
setting a target distance to a reference dimension
Reference dimension of azimuth
And the distance-to-reference resolution ρ required for imaging
refrAzimuthal reference resolution ρ
refaThen imaging of jth targetDirection-distance resolution ρ
jrAnd azimuthal resolution ρ
jaComprises the following steps:
wherein
Is the jth target range dimension,
Is the jth target azimuth dimension. Setting the minimum value of the azimuth resolution as rho
mina. The maximum frequency step length Δ f required to allow the radar to show the size profile of all targets without ambiguity at all
jComprises the following steps:
where c is the speed of light, the number of transmitted minimum sub-pulses N in the pulse train of the jth targetjComprises the following steps:
in order to meet the requirement of the required azimuth resolution for imaging the jth target, the number M of the required transmission pulse trainsjComprises the following steps:
wherein u is1A constant greater than 1 for adjusting the number of transmit bursts, λ being the signal wavelength, FPRFThe sub-pulse repetition frequency.
And (IV) estimating the target azimuth sparsity and the distance sparsity, wherein the specific process is as follows:
coarse resolution inverse synthetic aperture for jth targetRadial radar image SrjThe row with the largest element sum value in (k, l) was normalized to S 'as follows'rj(l) The element sum maximum column is normalized as S ″, as followsrj(k):
Setting a suitable threshold value to T
MIs prepared from S'
rj(l) Discretized representation is vector S'
rjWill be S ″)
rj(k) The discretization is represented as vector S ″
rjThen the azimuth sparsity of the jth target
And distance to sparsity
Comprises the following steps:
(V) determining the number L of target azimuth sparse transmission pulse trains by the radarjNumber Z of sub-pulses emitted to sparse by sum distancejThe specific process is as follows:
according to the compressed sensing theory, the number of pulse trains and the number of sub-pulses which are sparsely transmitted in the azimuth direction and the distance direction required by the jth target are respectively as follows:
wherein c is1Is a constant related to the recovery accuracy, and usually takes a value between 0.5 and 2.
And (VI) calculating the threat degree of the target by the following specific process:
calculation of the threat degree mainly considers the distance of the target
Speed of rotation
Course of course
Height
Four parameters, assuming that the radar needs to be on N
totallImaging an object, N
totallThese four factors affecting the threat for each target are written in the form of a matrix:
A=(aij)4×Ntotall (10)
in the formula, aij(i=1,2…,4;j=1,2…,Ntotall) A threat coefficient representing an ith factor of a jth target, i ═ 1,2 …,4 represent the distance of the target from the radar, the speed of the target, the heading of the target, and the altitude of the target, respectively, and j ═ 1,2 …, Ntotall;
Normalizing each factor to Y according to formula (11)ijThe weight of each factor is calculated as beta by the equation (12)i:
Wherein each factor occurs with a probability
If p is
ijWhen 0, then
Calculating the threat degree of the jth target according to the following formula:
wherein beta is1、β2、β3、β4And respectively obtaining weight coefficients for the distance from the target to the radar, the speed of the target, the course of the target and the height of the target.
(VII) under the condition of meeting the resource constraint, establishing a resource scheduling model and carrying out resource allocation, wherein the concrete process is as follows:
suppose the scheduling interval is T and the sub-pulse repetition frequency is FPRFThen the total number of sub-pulses within the scheduling interval: ptotall=T×FPRF;
Based on the basis, the following performance indexes are defined for the radar imaging resource scheduling algorithm:
(1) the sum of the target threat degrees of the radar completing the imaging task is as follows:
wherein N issRepresenting a target sequence number sequence for completing the imaging task in a scheduling interval T, wherein Nu is the number of targets for completing the imaging task in the scheduling interval;
(2) the scheduling success rate is as follows: the ratio of the number of targets actually and successfully executing the imaging tasks to the number of targets applying for executing the imaging tasks in the scheduling interval T is as follows:
wherein N istotallThe total number of targets for applying for executing the imaging tasks in the scheduling interval;
(3) the utilization rate of pulse resources is as follows: in the scheduling interval T, the ratio of the number of the sub-pulses occupied by the imaging task to the total number of the sub-pulses in the scheduling interval is completed:
(4) sum of performance indexes:
SPI=w1.STC+w2.SSR+w3.PRU (17)
wherein w1、w2、w3A weight coefficient.
Based on the performance indexes, a resource scheduling model is established as follows:
any pulse train of I'jiThe sum of the number of the sub-pulses in the pulse train is less than or equal to Nj
The resource scheduling model according to equation (18) can be described as:
step 1: setting the initial time j as 1, using the most front sub-pulse in the current rest idle pulse as the start position start for observing the j th target emission sub-pulsej;
Step 2: according to the number M of the sub-pulses required during the full-aperture observationj×NjDetermining the position of a terminator pulse of the task;
step 3: from the starting position to the end position by NjFor spacing, uniformly dividing MjA pulse train;
step 4: randomly picking out L from the currentjEach pulse train being randomly inserted Z within each selected pulse trainjAnd observing the sub-pulses.
Step 5: if j < NtotallAnd j equals j +1 and returns to the first step.
Step 6: obtaining a target sequence number sequence N for completing the imaging task within the scheduling interval T under the priority ordering modesThe number Nu of targets for completing the imaging task;
step 7: and calculating the sum of target threat degrees, scheduling success rate, pulse resource utilization rate and performance indexes of the radar for completing the imaging task in the priority sorting mode.
Adding the above-mentioned NtotallAnd (3) according to the principle that each combination in the priority sorting mode is substituted into the model to perform resource allocation according to the target priority, calculating the SPI of each combination through the allocation processes from Step1 to Step7, and selecting a pulse resource allocation sequence with the maximum Sum of Performance Indexes (SPI) and meeting the conditions of 3 constraints in the model as a final resource scheduling sequence result.
(VIII) obtaining a target two-dimensional image by using the existing two-dimensional sparse imaging technology, wherein the specific process is as follows:
and reasonably distributing radar pulse resources according to the resource scheduling model, alternately observing targets, and after receiving target echo signals, realizing inverse synthetic aperture radar two-dimensional imaging on each target by using the conventional two-dimensional sparse imaging technology.
By adopting the technical scheme of the invention, the resource allocation of the single-step radar facing to multiple targets can be realized from the aspects of the target azimuth direction and the distance direction, the radar resources are saved, and the overall performance of a radar system is improved.
Detailed Description
The following description will be made with reference to the accompanying drawings and examples, but the present invention is not limited thereto.
Example (b):
let T be 1s for scheduling interval and F for sub-pulse repetition frequencyPRF10kHz, the total number of sub-pulses within the scheduling interval: ptotall=T×F PRF10000, N in the scheduling interval TtotallThe individual target applies for an imaging task.
Fig. 1 shows a resource adaptive scheduling method for inverse synthetic aperture radar two-dimensional sparse imaging, which is implemented by calculating the pulse resource demand of each target on the basis of feature cognition of each target by a radar, determining the sub-pulse transmitting position required to be allocated to each target according to the constraint condition selected by the radar, and acquiring echoes through alternate observation of the targets, thereby completing the inverse synthetic aperture imaging task of multiple targets, and comprises the following steps:
the radar transmits a small amount of pulses to each target and estimates the flight parameters of the target, and the specific process is as follows:
the waveform parameters for estimating the target parameters of a small number of pulses transmitted by each target are set as follows: carrier frequency f
rcSub-pulse width T of 10GHz
rp0.3 mus, frequency step length Δ f
r3M, bandwidth B
r300 MHz. Randomly selecting 300 sub-pulses to transmit to each target, and measuring the distance between the jth target and the radar by using a radar conventional algorithm after radar echo signals are obtained
Target speed
Target course
Target height
The respective target parameters are shown in table 1.
TABLE 1 target parameter tables
(II) estimating the two-dimensional size of the target, wherein the specific process is as follows:
reconstruction F for filling zero in missing part of received echo dataPRFThe data of each observation point is used as the echo signal of the target coarse resolution inverse synthetic aperture radar image, and the echo signal of each target is processedThe wave signals are processed by inverse synthetic aperture radar imaging to obtain a rough image of each target, which is recorded as Srj(k, l). And normalizing the image to obtain a normalized image, which is recorded as S'rj(k,l):
Where k and l represent the target distance and azimuth envelope positions, respectively, according to the formula ρ
rr=c/(2B
r) Calculating the distance resolution according to
And calculating the azimuth resolution. Selecting a threshold value T
s0.38, the calculated distance is minimal towards the envelope position
And maximum distance to envelope position
According to the relation between the target distance and the envelope position, the distance dimension of the jth target can be obtained
Where ρ is
rr=c/(2B
r) Is the distance resolution; the minimum and maximum values of the position envelope position in the azimuth direction are calculated by the same method respectively
The azimuth dimension of the jth target can be obtained
Wherein
For azimuthal resolution, the two-dimensional recognition results for each target were calculated as shown in table 2 below.
TABLE 2 target feature recognition results
(III) determining the number of target transmission pulse trains and the number of sub-pulse transmissions under the pulse trains by the radar, and the specific process is as follows:
setting a target distance to a reference dimension
Reference dimension of azimuth
And the distance-to-reference resolution ρ required for imaging
refrAzimuthal reference resolution ρ
refaThe distance direction rho of the j th target required for imaging
jrAnd azimuthal resolution ρ
jaComprises the following steps:
wherein
Is the jth target range dimension,
Is the jth target azimuth dimension. Setting the minimum value of the azimuth resolution as rho
mina. The target distance is set to the reference dimension
An azimuth reference dimension of
Distance direction reference resolution is rho
refr0.5m and an azimuth reference resolution ρ
refa0.5m, the maximum frequency step length Δ f required to allow the radar to show the size profile of all targets completely unambiguous
jComprises the following steps:
where c is the speed of light, the number of transmitted minimum sub-pulses N in the pulse train of the jth targetjComprises the following steps:
in order to meet the requirement of the required azimuth resolution for imaging the jth target, the number M of the required transmission pulse trainsjComprises the following steps:
wherein u is1In order to adjust a constant greater than 1 for the number of the transmitted bursts, the value is 1.1, λ is the signal wavelength, and the results of calculating the number of the bursts to be transmitted for each target and the number of the sub-pulses transmitted under the bursts are shown in table 2 above.
And (IV) estimating the target azimuth sparsity and the distance sparsity, wherein the specific process is as follows:
coarse resolution inverse synthetic aperture radar image S for jth targetrjThe line normalization process for which the element sum value in (k, l) is the maximum is S'rj(l) The column normalization process with the largest sum of elements is S ″rj(k):
Setting the threshold value to T
M0.3, mixing S'
rj(l) Discretized representation is vector S'
rjThen the azimuth sparsity of the jth target
Is vector S'
rjIs greater than T
MThe number of elements (c). S ″)
rj(k) The discretization is represented as vector S ″
rjThen the distance of the jth target is sparse
Is vector S ″)
rjIs greater than T
MThe number of elements (c):
the results of estimation of the azimuth sparsity and the range sparsity of each target are shown in table 2 above.
And (V) determining the number of the target azimuth sparse transmission pulse trains and the number of the distance sparse transmission sub-pulses, wherein the specific process is as follows:
according to the compressed sensing theory, the number L of the pulse trains which are sparsely transmitted in the azimuth direction and the distance direction and are required by the jth targetjNumber of and subpulses ZjRespectively as follows:
wherein c is1The value of the constant is 0.51, and the estimation results of the number of the pulse trains emitted sparsely in each target direction and the number of the sub-pulses emitted sparsely in each target direction are shown in the table 2.
And (VI) calculating the threat degree of the target by the following specific process:
calculation of the threat degree mainly considers the distance of the target
Speed of rotation
Course of course
Height
Four parameters, assuming that the radar needs to be on N
totallImaging an object, N
totallThese four factors affecting the threat for each target are written in the form of a matrix:
A=(aij)4×Ntotall (10)
in the formula, aij(i=1,2…,4;j=1,2…,Ntotall) A threat coefficient representing an ith factor of a jth target, i ═ 1,2 …,4 represent the distance of the target from the radar, the speed of the target, the heading of the target, and the altitude of the target, respectively, and j ═ 1,2 …, Ntotall;
Normalizing each factor to Y according to formula (11)ijThe weight of each factor is calculated as beta by the equation (12)i:
Wherein each factor occurs with a probability
If p is
ijWhen 0, then
Calculating the threat degree of the jth target according to the following formula:
wherein beta is1、β2、β3、β4Weight coefficients are obtained for the distance from the target to the radar, the speed of the target, the heading of the target and the height of the target, respectively, and estimation results of the threat degrees of the targets are shown in table 2 above.
And (seventhly), under the condition of meeting the resource constraint, carrying out the specific process of resource allocation according to the resource scheduling model as follows:
setting 4 different priorities from high to low is: 0.4, 0.3, 0.2, 0.1, N for which there is a task application in the scheduling intervaltotallThe free ranking of 4 targets with 4 different priorities results in 24 prioritization as shown in table 3 below.
TABLE 3 target priority ranking list
Calculating the SPI of each combination in the 24 priority sorting modes according to the principle that each combination is firstly substituted into the following model for resource allocation according to the target priority:
pulse train I'
jiThe sum of the number of the sub-pulses in the pulse train is less than or equal to N
j
The impulse resource allocation procedure according to equation (18) can be described as:
step 1: setting the initial time j as 1, using the most front sub-pulse in the current rest idle pulse as the start position start for observing the j th target emission sub-pulsej;
Step 2: according to the number M of the sub-pulses required during the full-aperture observationj×NjDetermining the position of a terminator pulse of the task;
step 3: from the starting position to the end position by NjFor spacing, uniformly dividing MjA pulse train;
step 4: randomly picking out L from the currentjEach pulse train being randomly inserted Z within each selected pulse trainjAnd observing the sub-pulses.
Step 5: if j < NtotallAnd j equals j +1 and returns to the first step.
Step 6: obtaining a target sequence number sequence N for completing the imaging task within the scheduling interval T under the priority ordering modesThe number Nu of targets for completing the imaging task;
step 7: the sum of the target threat degrees, the scheduling success rate, the pulse resource utilization rate and the performance index of the radar completing the imaging task under the priority ranking mode is calculated as follows:
(1) the sum of the target threat degrees of the radar completing the imaging task is as follows:
wherein N issRepresenting a target sequence number sequence for completing the imaging task in a scheduling interval T, wherein Nu is the number of targets for completing the imaging task in the scheduling interval;
(2) the scheduling success rate is as follows: the ratio of the number of targets actually and successfully executing the imaging tasks to the number of targets applying for executing the imaging tasks in the scheduling interval T is as follows:
wherein N istotallAnd applying the total number of targets for executing the imaging tasks in the scheduling interval.
(3) The utilization rate of pulse resources is as follows: in the scheduling interval T, the ratio of the number of the sub-pulses occupied by the imaging task to the total number of the sub-pulses in the scheduling interval is completed:
(4) sum of performance indexes:
SPI=w1·STC+w2·SSR+w3·PRU (17)
wherein the weight coefficient is w1=0.3、w2=0.5、w3=0.2;
The ith pulse train transmitted by the radar to the jth target is I'ji。
And (3) according to the principle that each combination in the 24 priority ordering modes is substituted into the model to perform resource allocation according to the target priority, calculating the SPI of each combination through the allocation processes from Step1 to Step7, and selecting a pulse resource allocation sequence with the largest sum of the performance indexes and the SPI meeting the conditions of 3 constraints in the model as a final resource scheduling sequence result as shown in fig. 3 as shown in fig. 2.
(eighth) finally, obtaining a target two-dimensional image by using the existing two-dimensional sparse imaging technology, wherein the specific process is as follows:
and reasonably distributing radar pulse resources according to the resource scheduling model, alternately observing targets, and after receiving target echo signals, realizing inverse synthetic aperture radar two-dimensional imaging on each target by using the conventional two-dimensional sparse imaging technology.
By adopting the technical scheme of the invention, the resource allocation of the single-step radar facing to multiple targets can be realized from the aspects of the target azimuth direction and the distance direction, the radar resources are saved, and the overall performance of a radar system is improved.
The embodiments of the present invention have been described in detail with reference to the drawings and examples, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention.