阅读说明：本技术 一种估计pri值并提取脉冲序列的方法和装置 (Method and device for estimating PRI value and extracting pulse sequence ) 是由 张群英 成文海 董家铭 卢伟 刘小军 方广有 于 2021-09-01 设计创作，主要内容包括：本公开提供了一种估计PRI值并提取脉冲序列的方法和装置,通过融合周期识别准则和序列检索算法,能够在脉冲流同时存在较大PRI抖动和脉冲缺失的情况下,完成对PRI值相同或相近的雷达信号的分选,提高了分选正确率。(The invention provides a method and a device for estimating a pulse sequence (PRI) value and extracting the pulse sequence, which can finish the sorting of radar signals with the same or similar PRI values under the condition that pulse streams have larger PRI jitter and pulse loss at the same time by fusing a period identification criterion and a sequence retrieval algorithm, thereby improving the sorting accuracy.)

1. A method of estimating a PRI value and extracting a pulse sequence, comprising:

acquiring a pulse stream, an arrival time sequence of the pulse stream and a preset PRI value range;

dividing the preset PRI value range into at least one PRI box according to preset estimation precision, and calculating the frequency spectrum value of the at least one PRI box;

calculating a detection threshold of the at least one PRI box, wherein the PRI value of which the corresponding frequency spectrum value exceeds the detection threshold belongs to a to-be-selected PRI set;

screening a PRI value from the PRI set to be selected by using a period identification criterion to obtain an estimated PRI value of the first round of sorting;

selecting the pulses in the pulse stream one by one in sequence as initial pulses;

searching and separating a pulse corresponding to the estimated PRI value from the pulse stream according to the initial pulse to obtain a target pulse;

updating the estimated PRI value according to the target pulse to obtain an updated PRI value;

determining whether a next pulse of the target pulse exceeds a latest arrival time in the arrival time sequence of the pulse stream;

if the next pulse of the target pulse does not exceed the latest arrival time, taking the target pulse as a new initial pulse, and continuing to execute the step of searching and separating the pulse corresponding to the estimated PRI value from the pulse stream according to the initial pulse to obtain the target pulse;

if the next pulse of the target pulses exceeds the latest arrival time, judging whether the number of the target pulses separated from the pulse stream meets a first preset condition;

if the number of the target pulses separated from the pulse stream does not meet a first preset condition, adjusting the initial pulse;

if the number of the target pulses separated from the pulse stream meets a first preset condition, storing the separated target pulses as a pulse sequence, and adjusting the initial pulse;

judging whether the number of the initial pulse selected from the pulse stream is larger than a first threshold value or not, and if the number of the initial pulse selected from the pulse stream is smaller than or equal to the first threshold value, continuing to execute the step of sequentially selecting the pulses in the pulse stream one by one as the initial pulse;

if the number of the initial pulse selected from the pulse stream is greater than a first threshold value, ending the pulse sequence separation;

calculating the PRI value of each separated pulse sequence to obtain a PRI value sample set, and obtaining a sample center of the PRI value sample set, wherein the pulse sequence corresponding to the sample center is a target pulse sequence;

judging whether the number of the pulses remaining in the pulse stream is greater than a second threshold value, and if the number of the pulses remaining in the pulse stream is greater than the second threshold value, continuing to perform the step of calculating the frequency spectrum value of the at least one PRI box;

and if the number of the pulses remaining in the pulse stream is less than or equal to the second threshold value, finishing sorting.

2. The method according to claim 1, wherein the dividing the predetermined PRI value range into at least one PRI bin according to a predetermined estimation accuracy comprises:

dividing the preset PRI value range into H PRI boxes H according to the preset estimation precision_iIs the number of the PRI box, i is a positive integer, i ═ 1, 2., H;

h th_iCentral value of PRI boxComprises the following steps:

h th_iWidth of one PRI boxComprises the following steps:

where ε is the upper limit of the jitter of the PRI value, [ t [_min，t_max]Is the preset PRI value range, t_minIs the minimum value of the PRI value, t_maxIs the maximum value of the PRI value.

3. The method of estimating a PRI value and extracting a pulse sequence according to claim 2, wherein the calculating the spectral value of the at least one PRI bin specifically comprises:

selecting the nth pulse and the mth pulse from the pulse stream to obtain the arrival time t of the nth pulse_nAnd the arrival time t of the mth pulse_mWherein the initial value of n is 2, and the initial value of m is 1;

calculating the arrival time t of the nth pulse_nAnd the arrival time t of the m-th pulse_mTime difference τ between_nm，τ_nm＝t_n-t_m；

The calculation includes the time difference τ_nmOf PRI bins, wherein the minimum value of the number of PRI bins in the set P is h_x：

The maximum number of PRI boxes in the set P is h_d：

Wherein Δ τ ═ t_max-t_min)/H；

Then said time difference τ is included_nmThe set of PRI bins P of (a) is: p ═ h_x，...，h_d]Calculating the frequency spectrum value of each PRI box in the set P;

updating the n and the m to obtain n 'and m';

and repeating the steps according to the n ' and the m ' until the n ' meets a second preset condition.

4. The method of claim 3, wherein the updating n and m to obtain n 'and m' specifically comprises:

keeping n unchanged, updating m to obtain m', m ═ m-1;

judging whether m 'meets a third preset condition, and if m' does not meet the third preset condition, determining that n ═ n and m ═ m-1;

if m ' meets the third preset condition, determining that n ' meets a fourth preset condition, wherein n ' is n + 1;

if n ' does not satisfy the fourth preset condition, then m ' -n ' -1;

and if the n' meets the fourth preset condition, stopping the operation.

5. A method of estimating PRI values and extracting pulse sequences according to claim 3, wherein said calculating the spectral values of each PRI bin in said set P comprises:

extracting a PRI box from the set P to obtain an alternative PRI box h_τ；

Obtaining the alternative PRI boxes h_τInitial time of (O)_τTaking O_τ＝t_n；

Calculating the alternative PRI bins h_τInitial phase η of_τ；

The initial phase eta is measured_τDecomposing to obtain a decomposition result, and judging whether the decomposition result meets a fifth preset condition or not;

if the decomposition result meets the fifth preset condition, updating the alternative PRI box h_τInitial time of (O)_τAnd an initial phase η_τObtaining an updated initial time O_τ' and initial phase η_τ', based on said updated initial phase eta_τ' updating the alternative PRI boxes h_τSpectral value D of_τObtaining updated spectral values D_τ′；

If the decomposition result does not meet the fifth preset condition, directly updating the alternative PRI box h_τSpectral value D of_τObtaining updated spectral values D_τ′；

Continuing to extract a PRI box from the set P to obtain an alternative PRI box h_τUntil all PRI bins in the set P are extracted once;

wherein the content of the first and second substances,D_τ′＝D_τ+exp(2πiη_τ)，D_τspectral values, D, representing the accumulation of the # th PRI box before the update_τ' denotes the updated spectral values accumulated for the τ -th PRI bin.

6. The method of claim 2, wherein the calculating the detection threshold of the at least one PRI bin comprises:

calculating the detection threshold of each PRI box according to the following formula

Wherein alpha, beta and gamma are adjustable parameters,is the detection threshold at which the signal is detected,is the result of the pulse sequence autocorrelation frequency discrimination, T is the observation time of the pulse sequence, and p is the pulse density of the pulse stream.

7. The method for estimating PRI values and extracting pulse sequences according to claim 1, wherein the selecting a PRI value from the to-be-selected PRI set by using a period recognition criterion to obtain the first round of selected estimated PRI values specifically comprises:

assuming that the candidate set is Q,

Q＝[PRI₁，PRI₂，...，PRI_i]；

wherein i is a positive integer;

searching and counting the divisor of each PRI value in the to-be-selected set Q, wherein the PRI value with the largest divisor number is the estimated PRI value;

if the divisor number of at least two PRI values is the same, comparing the spectral values corresponding to the at least two PRI values, and taking the PRI value with the largest corresponding spectral value as the estimated PRI value.

8. The method of claim 1, wherein the searching and separating the pulse corresponding to the estimated PRI value from the pulse stream according to the start pulse to obtain the target pulse comprises:

obtaining the arrival time s (i) of the start pulse from the arrival time sequence of the pulse stream;

calculating the range of the target pulse:

calculating a position vector cnn of the target pulse satisfying a separation condition,

cnn＝find((s≥TOA_min)&(s≤TOA_max))；

updating the estimated PRI value according to the position vector of the target pulse;

where, toan is s (i), s is the time sequence of arrival of the pulse stream, PRI is the estimated PRI value, TOA_maxRepresenting the maximum value of the search range, TOA, of the target pulse corresponding to said estimated PRI value_minRepresents a minimum value, k, of a search range of a target pulse corresponding to said estimated PRI value_maxFor determining the maximum value, k, of the search range of the target pulse_minFor determining the minimum value of the search range of the target pulse, sck for counting, representing the number of PRIs between the target pulse and the current round of start pulses.

9. The method of claim 8, wherein the updating the estimated PRI value according to the position vector of the target pulse comprises:

calculating a value of length (cnn), if length (cnn) is 0, updating sck, where sck' is sck +1, and continuing to perform the step of calculating the position vector of the target pulse;

if length (cnn) ═ 1, the estimated PRI value is updated, the updated estimated PRI value is PRI',

if length (cnn) ≠ 0, and length (cnn) ≠ 1, then the estimated PRI value after updating is PRI ",

where s (tpnum) denotes the arrival time of the next pulse to be separated, and tt is used to count the number of existing pulses in the pulse sequence to be separated.

10. An apparatus for estimating PRI values and extracting pulse sequences, comprising:

the acquisition module is used for acquiring the pulse stream, the arrival time sequence of the pulse stream and a preset PRI value range;

the first calculation module is used for dividing the preset PRI value range into at least one PRI box according to preset estimation accuracy and calculating the frequency spectrum value of the at least one PRI box;

the second calculation module is used for calculating the detection threshold of the at least one PRI box, and the PRI value of which the corresponding frequency spectrum value exceeds the detection threshold belongs to a to-be-selected PRI set;

the first screening module is used for screening a PRI value from the PRI set to be selected by using a period identification criterion to obtain an estimated PRI value of the first round of sorting;

the separation module is used for sequentially selecting the pulses in the pulse stream one by one as initial pulses; and a pulse corresponding to the estimated PRI value is searched and separated from the pulse stream according to the starting pulse to obtain a target pulse;

the updating module is used for updating the estimated PRI value according to the target pulse to obtain an updated PRI value;

a first circulation module, configured to determine whether a next pulse of the target pulse exceeds a latest arrival time in the arrival time sequence of the pulse stream, and if the next pulse of the target pulse does not exceed the latest arrival time, continue to perform the step of searching and separating a pulse corresponding to the estimated PRI value from the pulse stream according to the start pulse by using the target pulse as a new start pulse to obtain a target pulse;

a second circulation module, configured to determine whether the number of target pulses separated from the pulse stream satisfies a first preset condition if a next pulse of the target pulses exceeds the latest arrival time, adjust an initial pulse if the number of target pulses separated from the pulse stream does not satisfy the first preset condition, and store the separated target pulses as a pulse sequence and adjust the initial pulse if the number of target pulses separated from the pulse stream satisfies the first preset condition;

a third circulation module, configured to determine whether a number of an initial pulse selected from the pulse stream is greater than a first threshold, and if the number of the initial pulse selected from the pulse stream is less than or equal to the first threshold, continue to perform the step of sequentially selecting pulses in the pulse stream one by one as the initial pulse; if the number of the initial pulse selected from the pulse stream is greater than a first threshold value, ending the pulse sequence separation;

the third calculation module is used for calculating the PRI value of each separated pulse sequence to obtain a PRI value sample set, and obtaining a sample center of the PRI value sample set, wherein the pulse sequence corresponding to the sample center is a target pulse sequence;

a determining module, configured to determine whether the number of remaining pulses in the pulse stream is greater than a second threshold, and if the number of remaining pulses in the pulse stream is greater than the second threshold, continue to perform the step of calculating the spectrum values corresponding to different PRI values within the preset PRI value range; and if the number of the pulses remaining in the pulse stream is less than or equal to the second threshold value, finishing sorting.

Technical Field

The present disclosure belongs to the field of Electronic Support systems (ESM) signal sorting, and in particular, relates to a method and an apparatus for estimating a pri (pulse Repetition interval) value and extracting a pulse sequence.

Background

Electronic Support Measures (ESM) are one of the most important components in electronic warfare. The ESM system is a device that measures radar radiation source parameters, identifies radiation source attributes, and determines radiation source threats using passive reception and signal processing techniques. In modern electronic warfare, Low Probability of Interception (LPI) signals adopted by a radar, system transmission loss, limitations of an ESM receiver and the like all cause a large number of pulse losses of a radar pulse sequence received by the ESM receiver. On the other hand, quantization errors, measurement noise and human intervention may also result in large PRI jitter of the received radar pulse sequence. In a complex electromagnetic environment, the radar signal intercepted by the ESM receiver is an approximately random radar pulse stream composed of a plurality of radar pulse sequences, and the approximately random radar pulse stream not only comprises a plurality of radar radiation sources, but also has the possibility of pulse missing and PRI jitter in the signal of each radiation source, and is referred to as a mixed pulse stream for convenience of description. Only after separating the intercepted mixed pulse stream into pulse sequences corresponding to different radar radiation sources can the radiation source properties be identified and corresponding countermeasures taken. The process of separating the mixed pulse stream into pulse sequences corresponding to different radar transmitters is called pulse sequence sorting.

There are many existing pulse sequence sorting algorithms, and the PRI transform algorithm is one important sorting algorithm. The conventional PRI transformation algorithm is an autocorrelation integral transformation algorithm, and can suppress the harmonic period of a periodic signal. However, conventional PRI transformation algorithms are sensitive to PRI jitter. The improved PRI transformation algorithm has good adaptability to PRI jitter and pulse loss by adopting a moving time starting point and an overlapped PRI box technology, but the algorithm cannot complete pulse sequence sorting when the PRI values of the pulse sequences are the same or similar.

BRIEF SUMMARY OF THE PRESENT DISCLOSURE

Technical problem to be solved

In view of the above-mentioned deficiencies of the prior art, it is a primary object of the present disclosure to provide a method and apparatus for estimating a PRI value and extracting a pulse sequence, which is intended to at least partially solve at least one of the above-mentioned technical problems.

(II) technical scheme

To achieve the above object, the present disclosure provides a method of estimating a PRI value and extracting a pulse sequence, the method including:

acquiring a pulse stream, an arrival time sequence of the pulse stream and a preset PRI value range;

dividing the preset PRI value range into at least one PRI box according to preset estimation accuracy, and calculating the frequency spectrum value of the at least one PRI box;

calculating a detection threshold of the at least one PRI box, wherein the PRI value of which the corresponding frequency spectrum value exceeds the detection threshold belongs to a to-be-selected PRI set;

screening a PRI value from the PRI set to be selected by using a period identification criterion to obtain an estimated PRI value of the first round of sorting;

selecting the pulses in the pulse stream one by one in sequence as initial pulses;

searching and separating the pulse corresponding to the estimated PRI value from the pulse stream according to the initial pulse to obtain a target pulse;

updating the estimated PRI value according to the target pulse to obtain an updated PRI value;

judging whether the next pulse of the target pulse exceeds the latest arrival time in the arrival time sequence of the pulse stream, if so, judging whether the number of the target pulses separated from the pulse stream meets a first preset condition, and if not, adjusting the starting pulse; if the number of the target pulses separated from the pulse stream meets a first preset condition, storing the separated target pulses as a pulse sequence, and adjusting the initial pulse;

if the next pulse of the target pulse does not exceed the latest arrival time, continuing to search and separate a pulse corresponding to the estimated PRI value from the pulse stream according to the initial pulse by taking the target pulse as a new initial pulse to obtain a target pulse;

judging whether the number of the initial pulse selected from the pulse stream is larger than a first threshold value or not, if the number of the initial pulse selected from the pulse stream is smaller than or equal to the first threshold value, continuing to execute the step of sequentially selecting the pulses in the pulse stream one by one as the initial pulse;

if the number of the initial pulse selected from the pulse stream is greater than a first threshold value, ending the pulse sequence separation;

calculating the PRI value of each separated pulse sequence to obtain a PRI value sample set, and obtaining the sample center of the PRI value sample set, wherein the pulse sequence corresponding to the sample center is a target pulse sequence;

determining whether the number of remaining pulses in the pulse stream is greater than a second threshold, and if the number of remaining pulses in the pulse stream is greater than the second threshold, continuing to perform the step of calculating spectrum values corresponding to different PRI values within the preset PRI value range;

and if the number of the pulses remaining in the pulse stream is less than or equal to the second threshold value, finishing the sorting.

In some embodiments, the dividing the preset PRI value range into at least one PRI bin according to a preset estimation accuracy specifically includes:

dividing the preset PRI value range into H PRI boxes H according to the preset estimation precision_iIs the number of the PRI box, i is a positive integer, i ═ 1, 2., H;

h th_iCentral value of PRI boxComprises the following steps:

h th_iWidth of one PRI boxComprises the following steps:

where ε is the upper limit of the jitter of the PRI value, [ t [_min，t_max]Is the above-mentioned predetermined PRI value range, t_minIs the minimum value of the PRI value, t_maxIs the maximum value of the PRI value.

In some embodiments, the calculating the spectrum value of the at least one PRI box specifically includes:

selecting the nth pulse and the mth pulse from the pulse stream to obtain the arrival time t of the nth pulse_nAnd the arrival time t of the m-th pulse_mWherein the initial value of n is 2, and the initial value of m is 1;

calculating the arrival time t of the nth pulse_nAnd the arrival time t of the m-th pulse_mTime difference τ between_nm，τ_nm＝t_n-t_m；

The calculation includes the above time difference τ_nmThe set P of PRI boxes, wherein the minimum value of the number of PRI boxes in the set P is h_x：

The maximum number of PRI boxes in the set P is h_d：

Wherein Δ τ ═ t_max-t_min)/H；

Then the above includes the above time difference τ_nmThe set of PRI bins P of (a) is: p ═ h_x，...，h_d]Calculating the frequency spectrum value of each PRI box in the set P;

updating the n and the m to obtain n 'and m';

and repeating the steps according to the n ' and the m ' until the n ' meets a second preset condition.

In some embodiments, the updating the n and the m to obtain n 'and m' specifically includes:

keeping n unchanged, updating m to obtain m', m ═ m-1;

determining whether m 'satisfies a third preset condition, and if m' does not satisfy the third preset condition, determining that n ═ n and m ═ m-1;

if m ' satisfies the third preset condition, determining whether n ' satisfies a fourth preset condition, if n ' is n + 1;

if n ' does not satisfy the fourth preset condition, then m ' is n ' -1;

if n' satisfies the fourth predetermined condition, the operation is stopped.

In some embodiments, the calculating the spectrum value of each PRI box in the set P includes:

extracting a PRI box from the set P to obtain an alternative PRI box h_τ；

Obtaining the alternative PRI box h_τInitial time of (O)_τTaking O_τ＝t_n；

Calculate the alternative PRI Box h_τInitial phase η of_τ；

The initial phase η_τDecomposing to obtain a decomposition result, and judging whether the decomposition result meets a fifth preset condition or not;

if the decomposition result satisfies the fifth predetermined condition, the alternative PRI box h is updated_τInitial time of (O)_τAnd an initial phase η_τObtaining an updated initial time O_τ' and initial phase η_τ', based on the updated initial phase eta_τ' update the alternative PRI Box h_τSpectral value D of_τObtaining updated spectral values D_τ′；

If the decomposition result does not satisfy the fifth preset condition, directly updating the alternative PRI box h_τSpectral value D of_τObtaining updated spectral values D_τ′；

Continuing to extract a PRI box from the set P to obtain an alternative PRI box h_τUntil all PRI boxes in the set P are extracted once;

wherein the content of the first and second substances,D_τ′＝D_τ+exp(2πiη_τ)，D_τspectral values, D, representing the accumulation of the # th PRI box before the update_τ' denotes the updated spectral values accumulated for the τ -th PRI bin.

In some embodiments, the calculating the detection threshold of the at least one PRI box specifically includes:

calculating the detection threshold of each PRI box according to the following formula

Wherein alpha, beta and gamma are adjustable parameters,is the above-mentioned detection threshold in the above-mentioned,is the result of the pulse sequence autocorrelation frequency discrimination, T is the observation time of the pulse sequence, and ρ is the pulse density of the pulse stream.

In some embodiments, the screening a PRI value from the to-be-selected PRI set by using the period identification criterion to obtain an estimated PRI value in the first round of sorting specifically includes:

assuming that the candidate set is Q,

Q＝[PRI₁，PRI₂，...，PRI_i]；

wherein i is a positive integer;

searching and counting the divisor of each PRI value in the to-be-selected set Q, wherein the PRI value with the largest divisor number is the estimated PRI value;

if the divisor number of at least two PRI values is the same, comparing the spectrum values corresponding to the at least two PRI values, and taking the PRI value with the largest corresponding spectrum value as the estimated PRI value.

In some embodiments, the searching and separating the pulse corresponding to the estimated PRI value from the pulse stream according to the start pulse to obtain the target pulse specifically includes:

obtaining an arrival time s (i) of the start pulse from the arrival time sequence of the pulse stream;

calculating the range of the target pulse:

the position vector cnn of the above-mentioned target pulse satisfying the separation condition is calculated,

cnn＝find((s≥TOA_min)&(s≤TOA_max))；

updating the estimated PRI value according to the position vector of the target pulse;

where, s is the time sequence of arrival of the pulse stream, PRI is the estimated PRI value, TOA_maxIndicating the maximum value of the search range, TOA, of the target pulse corresponding to the estimated PRI value_minIndicating the minimum value, k, of the search range of the target pulse corresponding to the estimated PRI value_maxFor determining the maximum value, k, of the search range of the target pulse_minThe minimum value of the search range for determining the target pulse, sck, is used for counting, and represents the number of PRIs between the target pulse and the start pulse of the current round.

In some embodiments, the updating the estimated PRI value according to the position vector of the target pulse specifically includes:

calculating a value of length (cnn), and if length (cnn) is 0, updating sck, where sck' is sck +1, and continuing the step of calculating the position vector of the target pulse;

if length (cnn) ═ 1, the estimated PRI value is updated, the updated estimated PRI value is PRI',

if length (cnn) ≠ 0, and length (cnn) ≠ 1, then the updated estimated PRI value is PRI ",

where s (tpnum) denotes the arrival time of the next pulse to be separated, and tt is used to count the number of existing pulses in the pulse sequence to be separated.

In another aspect, the present disclosure provides an apparatus for estimating a PRI value and extracting a pulse sequence, the apparatus comprising:

the acquisition module is used for acquiring the pulse stream, the arrival time sequence of the pulse stream and a preset PRI value range;

the first calculation module is used for dividing the preset PRI value range into at least one PRI box according to preset estimation accuracy and calculating the frequency spectrum value of the at least one PRI box;

a second calculating module, configured to calculate a detection threshold of the at least one PRI box, where a PRI value whose corresponding frequency spectrum value exceeds the detection threshold belongs to a to-be-selected PRI set;

the first screening module is used for screening a PRI value from the PRI set to be selected by using a period identification criterion to obtain an estimated PRI value of the first round of sorting;

the separation module is used for sequentially selecting the pulses in the pulse stream one by one as initial pulses; and a pulse corresponding to the estimated PRI value is searched and separated from the pulse stream according to the initial pulse to obtain a target pulse;

an updating module, configured to update the estimated PRI value according to the target pulse, so as to obtain an updated PRI value;

a first circulation module, configured to determine whether a next pulse of the target pulse exceeds a latest arrival time in an arrival time sequence of the pulse stream, and if the next pulse of the target pulse does not exceed the latest arrival time, continue to perform the step of searching and separating a pulse corresponding to the estimated PRI value from the pulse stream according to the start pulse by using the target pulse as a new start pulse to obtain a target pulse;

a second circulation module, configured to determine whether the number of target pulses separated from the pulse stream satisfies a first preset condition if a next pulse of the target pulses exceeds the latest arrival time, adjust an initial pulse if the number of target pulses separated from the pulse stream does not satisfy the first preset condition, and store the separated target pulses as a pulse sequence and adjust the initial pulse if the number of target pulses separated from the pulse stream satisfies the first preset condition;

a third circulation module, configured to determine whether a number of a start pulse selected from the pulse stream is greater than a first threshold, and if the number of the start pulse selected from the pulse stream is less than or equal to the first threshold, continue to perform the step of sequentially selecting pulses in the pulse stream one by one as a start pulse; if the number of the initial pulse selected from the pulse stream is greater than a first threshold value, ending the pulse sequence separation;

the third calculation module is used for calculating the PRI value of each separated pulse sequence to obtain a PRI value sample set, and obtaining a sample center of the PRI value sample set, wherein the pulse sequence corresponding to the sample center is a target pulse sequence;

a determining module, configured to determine whether the number of remaining pulses in the pulse stream is greater than a second threshold, and if the number of remaining pulses in the pulse stream is greater than the second threshold, continue to perform the step of calculating spectrum values corresponding to different PRI values within the preset PRI value range; and if the number of the pulses remaining in the pulse stream is less than or equal to the second threshold value, finishing the sorting.

(III) advantageous effects

According to the method for estimating the PRI value and extracting the pulse sequence, the period identification criterion and the sequence retrieval algorithm are fused, the radar signals with the same or similar PRI values can be sorted under the condition that the pulse stream has large PRI jitter and pulse loss at the same time, the sorting accuracy is improved, and the method has important significance for improving the functions and the performances of ESM and ECM.

Drawings

In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 schematically illustrates a flow chart of a method for estimating a PRI value and extracting a pulse sequence according to an embodiment of the present disclosure;

fig. 2 schematically illustrates a flowchart of a method for calculating spectral values of at least one PRI box according to an embodiment of the present disclosure;

FIG. 3 is a flow chart schematically illustrating a method for updating n and m according to an embodiment of the present disclosure;

fig. 4 schematically illustrates a flowchart of a method for calculating a spectrum value of each PRI box in the set P according to an embodiment of the present disclosure;

FIG. 5 is a schematic flow chart diagram illustrating a method for searching for and separating pulses corresponding to an estimated PRI value from a pulse stream based on a starting pulse according to one embodiment of the present disclosure;

FIG. 6 schematically illustrates a block diagram of an apparatus for estimating a PRI value and extracting a pulse sequence according to an embodiment of the present disclosure;

FIG. 7 schematically illustrates a graph of a mixed pulse train time of arrival (TOA) model provided by an embodiment of the present disclosure;

FIG. 8 is a graph schematically illustrating a first round of sorting results of a method of estimating PRI values and extracting pulse sequences provided by an embodiment of the present disclosure;

FIG. 9 is a diagram schematically illustrating a second round of sorting results of a method of estimating a PRI value and extracting a pulse sequence according to an embodiment of the present disclosure;

FIG. 10 schematically illustrates a third round of sorting results graph according to a method of estimating a PRI value and extracting a pulse sequence provided by an embodiment of the present disclosure;

FIG. 11 is a diagram schematically illustrating a fourth round of sorting results of a method of estimating a PRI value and extracting a pulse sequence according to an embodiment of the present disclosure;

fig. 12 schematically illustrates a graph of the average estimation error of the PRI value versus the PRI jitter provided by an embodiment of the present disclosure.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense.

Where a convention analogous to "at least one of A, B and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B and C" would include but not be limited to systems that have a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.). Where a convention analogous to "A, B or at least one of C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B or C" would include but not be limited to systems that have a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "a or B" should be understood to include the possibility of "a" or "B", or "a and B".

Some block diagrams and/or flow diagrams are shown in the figures. It will be understood that some blocks of the block diagrams and/or flowchart illustrations, or combinations thereof, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the instructions, which execute via the processor, create means for implementing the functions/acts specified in the block diagrams and/or flowchart block or blocks.

Fig. 1 schematically illustrates a flowchart of a method for estimating a PRI value and extracting a pulse sequence according to an embodiment of the present disclosure, where the method includes:

s101, acquiring a pulse stream, an arrival time sequence of the pulse stream and a preset PRI value range.

In this embodiment, a segment of a pulse stream, which includes a plurality of pulses, and a preset range of PRI values are obtained.

S102, dividing the preset PRI value range into at least one PRI box according to preset estimation accuracy, and calculating the frequency spectrum value of the at least one PRI box.

In this embodiment, in order to estimate the PRI value from the pulse stream, the range of the preset PRI value is divided according to the preset estimation accuracy to obtain a plurality of sub-ranges of the PRI value, where the sub-ranges of the PRI value have an intersection, and each sub-range of the PRI value is referred to as a PRI box.

S103, calculating a detection threshold of the at least one PRI box, wherein the PRI value of which the corresponding frequency spectrum value exceeds the detection threshold belongs to a to-be-selected PRI set.

S104, screening a PRI value from the PRI set to be selected by using a period identification criterion to obtain an estimated PRI value of the first round of sorting.

And S105, selecting the pulses in the pulse stream one by one in sequence as starting pulses.

And S106, searching and separating the pulse corresponding to the estimated PRI value from the pulse stream according to the initial pulse to obtain a target pulse.

And S107, updating the estimated PRI value according to the target pulse to obtain an updated PRI value.

And S108, judging whether the next pulse of the target pulse exceeds the latest arrival time in the arrival time sequence of the pulse stream.

And S109, if the next pulse of the target pulses does not exceed the latest arrival time, continuing to execute the step S106 by taking the target pulses as a new initial pulse.

And S110, if the next pulse of the target pulses exceeds the latest arrival time, judging whether the number of the target pulses separated from the pulse stream meets a first preset condition.

And S111, if the number of the target pulses separated from the pulse stream does not meet a first preset condition, adjusting the starting pulse.

And S112, if the number of the target pulses separated from the pulse stream meets a first preset condition, storing the separated target pulses as a pulse sequence, and adjusting the starting pulse.

S113, determining whether the number of the start pulse selected from the pulse stream is greater than a first threshold.

If the number of the start pulse selected from the pulse stream is less than or equal to the first threshold, the step S105 is continued.

And S114, if the number of the initial pulse selected from the pulse stream is greater than a first threshold value, ending the pulse sequence separation.

And S115, calculating the PRI value of each separated pulse sequence to obtain a PRI value sample set, and obtaining a sample center of the PRI value sample set, wherein the pulse sequence corresponding to the sample center is a target pulse sequence.

And S116, judging whether the number of the rest pulses in the pulse stream is larger than a second threshold value.

If the number of remaining pulses in the pulse stream is greater than the second threshold, the step S102 is continuously performed.

S117, if the number of pulses remaining in the pulse stream is less than or equal to the second threshold, the sorting is terminated.

In this embodiment, after a segment of pulse stream, an arrival time sequence of the pulse stream, and a preset PRI value range are obtained, the preset PRI value range is divided into a plurality of PRI bins according to preset estimation accuracy, only one PRI value is determined in each round of sorting by using a period identification criterion, signals with the same or similar PRI values can be sorted, and the sorting accuracy is improved.

In the present embodiment, in order to extract a true PRI value, the PRI bin corresponding to the true PRI value should be distinguished from other PRI bins, which is implemented by an observation time criterion, a harmonic reduction criterion, and a noise suppression criterion in the present embodiment.

In an embodiment of the present disclosure, dividing the preset PRI value range into at least one more PRI bin according to a preset estimation accuracy includes:

dividing the preset PRI value range into H PRI boxes H according to the preset estimation precision_iI is a positive integer, i is 1, 2, …, H, for the number of PRI bins.

H th_iCentral value of PRI boxComprises the following steps:

h th_iWidth of one PRI boxComprises the following steps:

where ε is the upper limit of the jitter of the PRI value, [ t [_min，t_max]For the above-mentioned predetermined PRI value range, t_minIs the minimum value of the PRI value, t_maxIs the maximum value of the PRI value.

Fig. 2 schematically illustrates a flowchart of a method for calculating spectrum values of at least one PRI box according to an embodiment of the present disclosure, and as shown in fig. 2, in an embodiment of the present disclosure, the method includes:

s201, selecting the nth pulse and the mth pulse from the pulse stream, and acquiring the arrival time t of the nth pulse_nAnd the arrival time t of the m-th pulse_mWherein n has an initial value of 2 and m has an initial value of 1.

S202, calculating the arrival time t of the nth pulse_nAnd the arrival time t of the m-th pulse_mTime difference τ between_nm，τ_nm＝t_n-t_m。

S203, calculating the time difference tau_nmThe set P of PRI boxes, wherein the minimum value of the number of PRI boxes in the set P is h_x：

The maximum number of PRI boxes in the set P is hd:

wherein Δ τ ═ t_max-t_min)/H；

Then the above includes the above time difference τ_nmThe set of PRI bins P of (a) is: p ═ h_x，...，h_d]。

And S204, calculating the spectrum value of each PRI box in the set P.

And S205, updating the n and the m to obtain n 'and m'.

S206, judging that the n' meets a second preset condition.

And S207, if the n' meets a second preset condition, ending the operation.

And S208, if the n ' does not meet the second preset condition, replacing n with n ', replacing m with m ', and continuing to execute the step S201. In this embodiment, the set P is determined by two pulses m and n extracted from the pulse stream, and a plurality of sets P can be obtained by updating m and n, so as to obtain a plurality of spectral values, and further estimate the PRI value from the pulse stream.

Fig. 3 schematically illustrates a flowchart of a method for updating n and m according to an embodiment of the present disclosure, and as shown in fig. 3, in an embodiment of the present disclosure, the method includes:

s301, updating m with n unchanged to obtain m', m ═ m-1.

S302, judging whether m' meets a third preset condition or not,

s303, if m ' does not satisfy the third preset condition, where n ' is n and m ' is m-1.

S304, if m 'satisfies the third predetermined condition, where n' is n +1,

s305, judging whether the n' meets a fourth preset condition.

S306, if n ' does not satisfy the fourth preset condition, the value m ' is n ' -1.

And S307, if the n' meets the fourth preset condition, stopping the operation.

In the present embodiment, the above-mentioned judgment of whether m 'satisfies the third preset condition means in the present embodiment that whether m' < 1 holds.

It should be noted that the third preset condition is that the meter m' < 1 is taken as an example, so that a person skilled in the art can understand the technical solution of the present disclosure, and the third preset condition of the present disclosure is not limited, and the third preset condition can be set according to actual requirements.

Fig. 4 schematically illustrates a flowchart of a method for calculating a spectrum value of each PRI box in a set P according to an embodiment of the present disclosure, and as shown in fig. 4, in an embodiment of the present disclosure, the method includes:

s401, extracting a PRI box from the set P to obtain an alternative PRI box h_τ。

S402, obtaining the alternative PRI box h_τInitial time of (O)_τTaking O_τ＝t_n。

S403, calculating the alternative PRI box h_τInitial phase η of_τ。

S404, converting the initial phase eta_τDecomposing to obtain a decomposition result,

s405, judging whether the decomposition result meets a fifth preset condition.

S406, if the decomposition result does not meet the fifth preset condition, directly updating the alternative PRI box h_τSpectral value D of_τObtaining updated spectral values D_τ′。

S407, if the decomposition result satisfies the fifth preset condition, updating the alternative PRI box h_τInitial time of (O)_τAnd an initial phase η_τObtaining an updated initial time O_τ' and initial phase η_τ', based on the updated initial phase eta_τ' update the alternative PRI Box h_τSpectral value D of_τObtaining updated spectral values D_τ′。

S408, judging whether all PRI boxes in the set P are extracted once.

If all the PRI boxes in the set P are not extracted once, the step S401 is continuously executed.

And S409, finishing the process if all the PRI boxes in the set P are extracted once.

Wherein the content of the first and second substances,D_τ′＝D_τ+exp(2πiη_τ)，D_τspectral values, D, representing the accumulation of the # th PRI box before the update_τ′Representing the updated spectral values accumulated for the # th PRI bin.

In this embodiment, the spectrum value of each PRI box in the set P needs to be calculated, and in the present disclosure, one PRI box is randomly extracted from the set P as an alternative PRI box, and then the spectrum value of the alternative PRI box is updated according to the initial phase and the initial time of the alternative PRI box.

In an embodiment of the present disclosure, the calculating the detection threshold of the at least one PRI box specifically includes:

calculating the detection threshold of different PRI values according to the following formula

Wherein alpha, beta and gamma are adjustable parameters,is the above-mentioned detection threshold in the above-mentioned,is the result of the pulse sequence autocorrelation frequency discrimination, T is the observation time of the pulse sequence, and ρ is the pulse density of the pulse stream.

In this embodiment, using the observation time criterion, assume a PRI value ofIs continued for an observation time T, the number of pulse streams is thenOn the other hand, in the case of a liquid,indicates a PRI value ofThe number of pulses in the pulse train of (a), ideally,in practical cases, however, due to the absence of pulses,the number of pulse streams is less than ideal, and the threshold based on the observation time criterion can be defined asWhere alpha is an adjustable parameter.

Using harmonic suppression criterion, supposeIs a PRI value of the radar pulse train, then in an ideal case, is the result of the pulse sequence autocorrelation frequency discrimination. If it is notIs a harmonic of the true PRI value in the pulse stream, thenThe threshold based on the harmonic rejection criterion is therefore:where β is an adjustable parameter. The threshold may effectively suppress harmonic components in the radar pulse train in the presence of PRI jitter.

By using the noise reduction criterion, in order to detect the true PRI value, it is necessary to ensure that the PRI spectrum value of the PRI box corresponding to the true PRI value is much larger than the noise value (the PRI box corresponding to the true PRI value and its harmonic is removed, and the PRI spectrum values corresponding to other PRI boxes are referred to as noise values). In the conventional PRI transformation, ifIs a noise component, thenThe variance of the values is less thanWhere p is the pulse density of the pulse stream,is the case width of the first PRI case. On the basis of this variance, a threshold for filtering the noise value is proposed as:where gamma is an adjustable parameter. In a conventional PRI transform, a 3-fold variance criterion is used, i.e., γ — 3. The noise level in the improved PRI transform is much greater than that in the conventional PRI transform. Therefore, in improving the PRI transformation, the value of γ is much less than 3.

Combining the three criteria to obtain the detection threshold of the PRI transformation algorithm

Where α, β and γ are adjustable parameters, their values can be changed under different conditions to increase the detection probability and decrease the false alarm probability.

In an embodiment of the present disclosure, the screening a PRI value from the to-be-selected PRI set by using a period identification criterion to obtain an estimated PRI value in a first round of sorting specifically includes:

assuming that the candidate set is Q,

Q＝[PRI₁，PRI₂，...，PRI_i]wherein i is a positive integer.

And searching and counting the divisor of each PRI value in the candidate set Q, wherein the PRI value with the largest divisor number is the estimated PRI value.

If the divisor number of at least two PRI values is the same, comparing the spectrum values corresponding to the at least two PRI values, and taking the PRI value with the largest corresponding spectrum value as the estimated PRI value.

In this embodiment, only one PRI value is determined in each round of sorting by using the period identification criterion, and meanwhile, because there may be a spread signal in the pulse stream, when the sub-pulse interval of the reference signal is a divisor of the frame period of the reference signal, the sub-pulse interval may be identified as the PRI value of the pulse sequence, and the sequence separation performed by using the PRI value may destroy the periodicity of the original spread signal, resulting in sorting failure.

Fig. 5 is a schematic flow chart illustrating a method for searching and separating a pulse corresponding to an estimated PRI value from a pulse stream according to a starting pulse according to an embodiment of the present disclosure, as shown in fig. 5, in an embodiment of the present disclosure, the method includes:

s501, obtaining the arrival time S (i) of the start pulse from the arrival time sequence of the pulse stream.

S502, calculating the range of the target pulse:

s503, calculating the position vector cnn of the target pulse meeting the separation condition,

cnn＝find((s≥TOA_min)&(s≤TOA_max))。

and S504, updating the estimated PRI value according to the position vector of the target pulse.

Where, s is the time sequence of arrival of the pulse stream, PRI is the estimated PRI value, TOA_maxIndicating the maximum value of the search range, TOA, of the target pulse corresponding to the estimated PRI value_minIndicating the minimum value, k, of the search range of the target pulse corresponding to the estimated PRI value_maxFor determining the maximum value, k, of the search range of the target pulse_minThe minimum value of the search range for determining the target pulse, sck, is used for counting, and represents the number of PRIs between the target pulse and the start pulse of the current round.

In this embodiment, the found estimated PRI value is used as an initial PRI value, the PRI value is updated once per pulse separation until the separation of the pulse stream is completed, there may be a plurality of pulse sequences satisfying requirements for a given PRI value, the PRI value of each pulse sequence is calculated, the PRI value is used as a sample, the euclidean distance is used as a similarity measure, the center of the sample is found, and the pulse sequence corresponding to the center of the sample is the finally separated pulse sequence.

In an embodiment of the present disclosure, the updating the estimated PRI value according to the position vector of the target pulse specifically includes:

calculating a value of length (cnn), updating sck if length (cnn) is 0, and continuing the step of calculating the position vector of the target pulse if updated sck is sck' ═ sck + 1.

If length (cnn) ═ 1, the estimated PRI value is updated, the updated estimated PRI value is PRI',

if length (cnn) ≠ 0, and length (cnn) ≠ 1, then the updated estimated PRI value is PRI ",

where s (tpnum) denotes the arrival time of the next pulse to be separated, and tt is used to count the number of existing pulses in the pulse sequence to be separated.

In an embodiment of the present disclosure, the radar signal simulation model is a time of arrival (TOA) model as shown in fig. 7, and the main simulation parameters are shown in table 1.

TABLE 1 Mixed pulse sequence 1 parameter Table

Parameter(s)	Pulse sequence 1	Pulse sequence 2	Pulse sequence 3	Pulse sequence 4
					PRI value (μ s)	27	35	35	47
Jitter range	±10％	±10％	±10％	±10％
					Noise error	±3％	±3％	±3％	±3％
Pulse loss rate	±10％	±10％	±10％	±10％
					Total Observation time (μ s)	5000	5000	5000	5000

The simulation results are shown in fig. 8 to 11. The sorting is carried out for four rounds, the first round of sorting has 3 PRI values exceeding the detection threshold, and the PRI values are identified according to the period₁35.04 μ s is the first round PRI identification result; the second round of sorting has 3 PRI values exceeding the detection threshold, according to the period identification criterion, PRI₂26.972 μ s is the second round of PRI identification; the third round of sorting has 2 PRI values exceeding the detection threshold, according to the period identification criterion, PRI₃Third round of PRI identification result is 34.81 μ s; the fourth sorting pass has a PRI value exceeding the detection threshold, PRI₄46.92 mus for the fourth wheelPRI identification results. According to simulation results, under the conditions of loss and jitter of pulse streams, the novel PRI transformation algorithm can complete sorting of pulse sequences with the same PRI value, and the PRI value estimation precision is high.

To further verify the effectiveness of the novel PRI transformation algorithm, the present disclosure selects the performance of the PRI mean estimation error evaluation algorithm, where the mean estimation error is defined as follows:

wherein the content of the first and second substances,indicating an estimated PRI value, PRI_iRepresenting the actual PRI value and n representing the number of pulse trains.

A segment of the mixed radar signal pulse stream was selected with the parameters shown in table 2.

TABLE 2 Mixed pulse sequence 2 parameter Table

The simulation results are shown in fig. 12. According to simulation results, under the condition that the pulse missing rate is 10%, when the PRI jitter is not more than + 12%, the PRI estimation accuracy is good, and when the PRI jitter is more than + 12%, the algorithm can still complete pulse sequence sorting, and the estimation accuracy is slightly reduced.

Based on the method for estimating the PRI value and extracting the pulse sequence, the disclosure also provides a device for estimating the PRI value and extracting the pulse sequence.

Fig. 6 schematically illustrates a block diagram of an apparatus for estimating a PRI value and extracting a pulse sequence according to an embodiment of the present disclosure, and as shown in fig. 6, in an embodiment of the present disclosure, the apparatus 600 includes an obtaining module 601, a first calculating module 602, a second calculating module 603, a first screening module 604, a separating module 605, an updating module 606, a first circulating module 607, a second circulating module 608, a third circulating module 609, a third calculating module 610, and a determining module 611.

The obtaining module 601 is configured to obtain a pulse stream, an arrival time sequence of the pulse stream, and a preset PRI value range. In an embodiment, the obtaining module 601 may be configured to perform the foregoing S101, which is not described herein again.

The first calculating module 602 is configured to divide the preset PRI value range into at least one PRI bin according to a preset estimation accuracy, and calculate a spectrum value of the at least one PRI bin. In an embodiment, the first calculating module 602 may be configured to perform the foregoing S102, which is not described herein again.

A second calculating module 603, configured to calculate a detection threshold of the at least one PRI box, where a PRI value of which a corresponding spectrum value exceeds the detection threshold belongs to a to-be-selected PRI set. In an embodiment, the second calculating module 603 may be configured to perform the foregoing S103, which is not described herein again.

The first screening module 604 is configured to screen a PRI value from the to-be-selected PRI set by using a period identification criterion, so as to obtain an estimated PRI value for the first round of sorting. In an embodiment, the first filtering module 604 may be configured to perform the foregoing S104, which is not described herein again.

A separation module 605, configured to select the pulses in the pulse stream one by one in sequence as the start pulse. And the pulse generator is used for searching and separating the pulse corresponding to the estimated PRI value from the pulse stream according to the starting pulse to obtain a target pulse. In an embodiment, the separation module 605 may be configured to perform the foregoing S105-S106, which is not described herein again.

An updating module 606, configured to update the estimated PRI value according to the target pulse, so as to obtain an updated PRI value. In an embodiment, the updating module 606 may be configured to perform the foregoing S107, which is not described herein again.

A first circulation module 607, configured to determine whether a next pulse of the target pulse exceeds a latest arrival time in the arrival time sequence of the pulse stream, and if the next pulse of the target pulse does not exceed the latest arrival time, continue to perform the step of searching and separating a pulse corresponding to the estimated PRI value from the pulse stream according to the start pulse by using the target pulse as a new start pulse to obtain a target pulse. In an embodiment, the first loop module 607 can be configured to perform the operations of S108-S109 described above, which are not described herein again.

A second circulation module 608, configured to determine whether the number of target pulses separated from the pulse stream satisfies a first preset condition if the next pulse of the target pulses exceeds the latest arrival time, adjust the start pulse if the number of target pulses separated from the pulse stream does not satisfy the first preset condition, and store the separated target pulses as a pulse sequence and adjust the start pulse if the number of target pulses separated from the pulse stream satisfies the first preset condition. In one embodiment, the second loop module 608 can be used to perform the operations of S110-S112 described above, which are not described herein again.

A third circulation module 609, configured to determine whether the number of the start pulse selected from the pulse stream is greater than a first threshold, and if the number of the start pulse selected from the pulse stream is less than or equal to the first threshold, continue to perform the step of sequentially selecting the pulses in the pulse stream one by one as the start pulse. And if the number of the initial pulse selected from the pulse stream is larger than a first threshold value, ending the pulse sequence separation. In an embodiment, the third loop module 609 can be configured to perform the operations of S113-S114 described above, which are not described herein again.

The third calculating module 610 is configured to calculate a PRI value of each separated pulse sequence, obtain a PRI value sample set, and obtain a sample center of the PRI value sample set, where a pulse sequence corresponding to the sample center is a target pulse sequence. In an embodiment, the third calculating module 610 may be configured to perform the foregoing S115, which is not described herein again.

The determining module 611 is configured to determine whether the number of remaining pulses in the pulse stream is greater than a second threshold, and if the number of remaining pulses in the pulse stream is greater than the second threshold, continue to perform the step of calculating the spectrum values corresponding to different PRI values within the preset PRI value range. And if the number of the pulses remaining in the pulse stream is less than or equal to the second threshold value, finishing the sorting. In an embodiment, the determining module 611 may be configured to perform the foregoing S116-S117, which is not described herein again.

The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams or flowchart illustration, and combinations of blocks in the block diagrams or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

Those skilled in the art will appreciate that various combinations and/or combinations of features recited in the various embodiments and/or claims of the present disclosure can be made, even if such combinations or combinations are not expressly recited in the present disclosure. In particular, various combinations and/or combinations of the features recited in the various embodiments and/or claims of the present disclosure may be made without departing from the spirit or teaching of the present disclosure. All such combinations and/or associations are within the scope of the present disclosure.

While the disclosure has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. Accordingly, the scope of the present disclosure should not be limited to the above-described embodiments, but should be defined not only by the appended claims, but also by equivalents thereof.