CN103513239A - Method of inhibiting direct wave interference by employing code phase modulation signal - Google Patents

Abstract

The invention discloses a method of inhibiting direct wave interference by employing code phase modulation signals. The method comprises the steps of determining central frequency, bandwidth and pulse width of code phase modulation signals; adjusting coding forms and phase information of the code phase modulation signals, generating all candidate emission signals, calculating autocorrelation coefficients, screening the candidate emission signals and obtaining a preliminary emission signal set; calculating cross correlation characteristics of all signals in the set for the preliminary emission signal set, further screening the emission signals and obtaining a new emission signal set; and calculating fuzziness functions of signals in the emission signal set, obtaining doppler tolerance through the fuzziness functions, converting the doppler tolerance into theory velocity measurement precision, comparing the theory velocity measurement precision of each signal in the emission signal set with an allowed velocity variation scope of an active sonar task target and then selecting suitable emission signals in the emission signal set based on a comparison result.

Description

A kind of coding phase-modulated signal that adopts is realized the method that direct-wave jamming suppresses

Technical field

The present invention relates to active sonar digital processing field, particularly a kind of coding phase-modulated signal that adopts is realized the method that direct-wave jamming suppresses.

Background technology

During ship proceed in formation at sea, the active sonar on ship not only can be received the echoed signal that comes from target, also can not timing receive the same frequency direct-wave jamming signal that comes from friendly ship.Due to the restriction of hardware facility and environmental baseline, the usable frequency bandwidth limited that each ship transmits, causes the detection performance on naval vessel greatly to reduce.How effectively reducing friendly ship co-channel interference signal is a urgent problem solving of needs in active sonar design on the impact of result of detection.The spacing of forming into columns due to naval vessel is less, and co-channel interference direct wave experience is one-way attenuation, and therefore at receiving end, its energy can exceed tens decibels than target echo.After processing through energy detector, still much larger than the output of echo, there is obvious false-alarm in the output of direct-path signal.Therefore need to suppress direct-wave jamming signal.

Traditional direct-wave jamming inhibition method is generally started with from Beam Domain, for example MVDR based on spatial filtering, Schimidt orthogonalization method, or the wavenumber domain DICANNE method of subtracting each other, and LMS filtering method etc.The basic thought of MVDR and Schimidt orthogonalization method is to form one group of coefficient, and making at expectation beam direction is all-pass, and minimum in the interference radiating way response of setting.This is optimum in theory algorithm, but very sensitive for mismatch, such as the mismatch of expectation beam direction and actual signal direction, array response mismatch etc.If but accurate to the estimation of interference radiating way, even so target echo and direct wave overlapping in time domain, also can obtain the testing result of expectation.DICANNE method forms wave beam at interference radiating way, obtains undesired signal, carries out from other wave beams, cutting this signal after time delay correction.The method pair array delay precision is had relatively high expectations, exigent sampling rate (96kHz) in addition, and when jamming-to-signal ratio is very high, the point that misplaces, effect is just very poor.LMS filtering method is first to form interfering beam, and using it as wanted signal, then to other wave beam filtering, remaining error signal is echo signal.When realizing, the method is generally using MVDR interfering channel before as wanted signal, then the data after MVDR is done to LMS filtering.Similar with DICANNE method, LMS filtering method is also very sensitive to time delay error.In addition, also have a kind of low level method for cutting, by controlling the number of significant digit of data, retain high-order data.Low level method for cutting requires signal envelope to rise and fall can not be too violent, i.e. strong multipath interference can largely reduce the performance of method, and requires undesired signal not in amplitude limit state.

The applicant finds through research, to be issued to this requirement of anti-co-channel interference in formation condition, need a kind of signal that can produce a plurality of different copies, and these copy signal to have the good and cross correlation of autocorrelation be zero or almost nil characteristic, like this under formation condition, as long as each ship is used different copy signal, just can the non-interfering active probe of carrying out.Active sonar is surveyed also has another one problem under formation condition, while carrying out exactly active sonar detection, a certain ship can be received the direct-path signal of the coded signal of another copy that other ships send, the energy of this direct-path signal is than high tens decibels of target echo energy, and this can impact the detection of target echo signal.

For example: meet 1 kilometer in A, two formation naval vessels of B, all launch active signal and sound source level SL is identical, signal frequency is 7.5kHz, target is at distance A warship 3 kms, target echo signal energy E target=SL-2TL (3km)-NL(ground unrest that A warship receives)+TS(target reflection strength), and the active signal energy of the B warship that A warship receives transmitting is E_B=SL-TL (1km)-NL, so energy difference Δ E=E_B-Etarget=2TL (3km)-TL (the 1km)-TS=130-62-15 between them (look into propagation attenuation curve, and get TS be 15 decibels)=53dB.And if 10 kilometers, target range A warship, this energy difference Δ E is 73dB.Be that this energy difference is between 53-73dB.So in this case, if the dynamic range of AD sampling thief is too small, direct wave makes the complete amplitude limit of receiving end signal, will detect the weak echo signal of target.Under the poor condition of this high-energy, conventional signal processing method is difficult to detect target echo signal.

In sum, all there is defect separately in existing direct-wave jamming inhibition method, cannot meet user's demand completely.

Summary of the invention

The object of the invention is to overcome the existing defect of existing direct-wave jamming inhibition method, thereby a kind of successful is provided, realize simple direct-wave jamming inhibition method.

To achieve these goals, the invention provides a kind of coding phase-modulated signal that adopts and realize the method that direct-wave jamming suppresses, comprise

Centre frequency, bandwidth and the pulsewidth of step 1), definite coding phase-modulated signal;

Step 2), adjust coding form and the phase information of coding phase-modulated signal, generate all candidate transmitting signals, then calculate coefficient of autocorrelation, according to described coefficient of autocorrelation, described candidate transmitting signal is screened, obtain the preliminary set that transmits;

Step 3), for step 2) the preliminary set that transmits that obtains, calculate the their cross correlation between all signals in this set, according to described their cross correlation, described transmitting done to further screening, obtain the new set that transmits;

Step 4), calculation procedure 3) ambiguity function of signal in the set that transmits that obtains, by described ambiguity function, obtain doppler tolerance, then convert described doppler tolerance to theoretical rate accuracy, finally the theoretical rate accuracy of each signal and the permission speed of a ship or plane mobility scale of active sonar task object in the described set that transmits are compared, what in the set that transmits described in selecting according to comparative result, be applicable to transmits.

In technique scheme, in described step 2) in, the coding form of adjusting described coding phase-modulated signal comprises adjusts code element number and coded sequence.

In technique scheme, in described step 2) in, calculate coefficient of autocorrelation and comprise:

Step 2-1) signal, to each acquisition, calculates its coefficient of autocorrelation group, and computing formula is as follows:

$c_k=\underset{j=1}{\overset{n-k}{\mathrm{\Σ}}}{e}^{i(t_j-t_{j+k})}$

Wherein, c _krepresenting the coefficient of autocorrelation that k kind is possible, k span is 1 ~ integer within (n-1); t _jrepresent a _jcorresponding phase information, and t _j+krepresent a _j+kcorresponding phase information; E and ∑ are the sign of operation of standard; A=[a ₁, a ₂..., a _n] be the sampled value of digital signal,

Step 2-2), from resulting coefficient of autocorrelation group, according to following formula, choose the coefficient of autocorrelation of maximum possible:

l=max{|c _k|:1≤k≤n-2}。

In technique scheme, in described step 3), calculate cross-correlation coefficient and comprise:

Two signals are A=[a ₁, a ₂..., a _n] and B=[b ₁, b ₂..., b _n], their cross correlation array expression formula is as follows: $c_k=\underset{j=1}{\overset{n-k}{\mathrm{\Σ}}}{e}^{i(t_j-s_{j+k})}$

Wherein

a _j, b _jrepresent respectively two signal sampling values, t _j, s _jrepresent respectively a _j, b _jcorresponding phase information;

From resulting cross correlation array, according to following formula, calculate the cross-correlation coefficient of maximum possible:

p=max{|c _k|:1≤k≤n-2}

The invention has the advantages that:

The present invention has successful, realizes simple advantage.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of direct-wave jamming inhibition method of the present invention;

Fig. 2 is under little signal to noise ratio (S/N ratio) condition, the schematic diagram of coding phase-modulated signal to the time domain waveform of the reception signal of 4 targets;

Fig. 3 is the schematic diagram that receives the matched filtering result of signal shown in Fig. 2;

Fig. 4 is the schematic diagram that receives the matched filtering result of signal after Doppler shift in Fig. 2;

Fig. 5 is under large signal to noise ratio (S/N ratio) condition, adopts the schematic diagram of the direct-wave jamming inhibition result of coding phase-modulated signal;

Fig. 6 is under little signal to noise ratio (S/N ratio) condition, adopts the schematic diagram of the direct-wave jamming inhibition result of coding phase-modulated signal.

Embodiment

Now the invention will be further described by reference to the accompanying drawings.

In background technology, mention, be issued to this requirement of anti-co-channel interference in formation condition, need a kind of signal that can produce a plurality of different copies, and these copy signal have that autocorrelation is good and cross correlation is zero or almost nil characteristic.Therefore, the work that direct-wave jamming inhibition method of the present invention will complete is according to the feature of active sonar detection mission, to determine centre frequency and the bandwidth of coding phase-modulated signal, then look for the satisfactory coding form of correlation properties, and obtaining its Doppler effect correction characteristic (being moving object detection performance), resulting coding phase-modulated signal can be realized direct-wave jamming inhibition thus.

With reference to figure 1, direct-wave jamming inhibition method of the present invention comprises the following steps:

Centre frequency, bandwidth and the pulsewidth of step 1), definite coding phase-modulated signal.

The value of the centre frequency of coding phase-modulated signal is closely related with the size that receives battle array, and optimum value should meet the half-wavelength that the receives battle array condition of structuring the formation.In addition, center frequency value also needs the mobility scale with reference to detection range, and generally, long-range detection needs lower centre frequency, and proximity detection needs higher centre frequency.The value of bandwidth and the Size dependence of expectation target, pulsewidth is limited to the power amplifier ability of transmitting transducer.

Step 2), adjust coding form (being mainly the change of code element number and coded sequence) and the phase information of coding phase-modulated signal, calculate corresponding coefficient of autocorrelation, obtain the preliminary set that transmits.

In step 1), determine after centre frequency, bandwidth and the pulsewidth of coding phase-modulated signal, first coding form and the phase information of the coding phase-modulated signal that will generate are adjusted in this step.The adjustment of described coding form comprises the change of code element number and coded sequence.In the present embodiment, the evolutionary mode of code element number, for to increase progressively according to binary mode, in other embodiments, also can adopt other feasible modes in prior art.The evolutionary mode of coded sequence is likely sequence of traversal institute, for example, have L code element, can be accordingly (factorial) plants coded sequence.The phase place variation range of coding phase-modulated signal is-180 ° ~ 180 °, when phase information is adjusted, need to, with certain resolution (as adopted 0.5° interval) traversal, generate 720 kinds of possible phase places.

Coding form by before and the adjustment of phase information obtain after a plurality of candidate transmitting signals, are these candidate transmitting calculated signals coefficient of autocorrelation.The account form of described coefficient of autocorrelation is as follows:

Step a), the signal to each acquisition, calculate its coefficient of autocorrelation group, and computing formula is as follows:

$c_k=\underset{j=1}{\overset{n-k}{\mathrm{\Σ}}}{e}^{i(t_j-t_{j+k})}---\left(1\right)$

Wherein, c _krepresenting the coefficient of autocorrelation that k kind is possible, k span is 1 ~ integer within (n-1); t _jrepresent a _jcorresponding phase information, and t _j+krepresent a _j+kcorresponding phase information; E and ∑ are the sign of operation of standard.A=[a ₁, a ₂..., a _n] be the sampled value of digital signal,

Step b), from resulting coefficient of autocorrelation group, according to following formula (2), choose the coefficient of autocorrelation of maximum possible:

l＝max{|c _k|:1≤k≤n-2} （2）

After obtaining the coefficient of autocorrelation of signal maximum possible, can to all candidate transmitting signals, do primary screening according to coefficient of autocorrelation.For example, for all possible signal, retain the signal that l value is greater than 0.995.

Step 3), for step 2) the preliminary set that transmits that obtains, calculate the their cross correlation between all signals in the set that transmits, according to their cross correlation, do further screening.

Suppose that two signals are A=[a ₁, a ₂..., a _n] and B=[b ₁, b ₂..., b _n], their cross correlation array expression formula is as follows:

$c_k=\underset{j=1}{\overset{n-k}{\mathrm{\Σ}}}{e}^{i(t_j-s_{j+k})}---\left(3\right)$

Wherein

a _j, b _jrepresent respectively two signal sampling values, t _j, s _jrepresent respectively a _j, b _jcorresponding phase information.

From resulting cross correlation array, can calculate according to following formula the cross-correlation coefficient of maximum possible:

p＝max{|c _k|:1≤k≤n-2} （4）

After obtaining the cross-correlation coefficient of signal maximum possible, can to all candidate transmitting signals, do primary screening according to cross-correlation coefficient.If selected to comprise N signal in signal set, the p value that each signal is corresponding is so N-1.If the value of the N-1 of a some signals p all, lower than a threshold value (as 0.0249), retains this signal so, otherwise this signal is deleted from candidate transmitting signal.

Step 4), calculation procedure 3) ambiguity function of signal in the set that transmits that obtains, by ambiguity function, obtain doppler tolerance, then doppler tolerance is converted to theoretical rate accuracy.The theoretical rate accuracy of each signal and the permission speed of a ship or plane mobility scale of active sonar task object in the set that transmits are compared, and what according to comparative result, selection was applicable in transmitting and gathering transmits.

In this step, described ambiguity function expression formula is:

Wherein

be respectively time delay and the phase information of signal, for the time domain of signal is expressed,

for the time delay conjugation time domain of signal is expressed,

the amplitude corresponding for phase place changes.How by ambiguity function, to calculate the common practise that doppler tolerance is those skilled in the art, at this, no longer describe in detail.

The theoretical rate accuracy transmitting need to further be verified via experiment.In pond or open waters, use transmitting of having chosen to survey the target of different motion speed.Carry out to the received signal Doppler's estimation, obtain velocity estimation value, described velocity estimation value and actual measurement target speed are compared, if error range is less, retains this and transmit.

By above-mentioned steps, obtain encoding after phase-modulated signal, this signal is launched by active sonar, can effectively avoid direct-wave jamming.

In an experimental example, transmitting battle array adopts a linear array, receives battle array and adopts a semi arch battle array, and be 30kHz according to the centre frequency that the parameter of basic matrix arranges transmit signal pulse, and bandwidth is 4kHz.

Fig. 2 is under little signal to noise ratio (S/N ratio) condition, the time domain waveform of coding phase-modulated signal to the reception signal of 4 targets.Wherein: target 1 is that signal to noise ratio (S/N ratio) is-static target of 14.2dB; Target 2 be signal to noise ratio (S/N ratio) be-14dB with the 2 joint speed of a ship or plane near this ship to navigation motion ship target; Target 3 is that signal to noise ratio (S/N ratio) is-static target of 17dB; Target 4 be signal to noise ratio (S/N ratio) be-17dB with the 4 joint speed of a ship or plane away from this ship to navigation motion ship target.

Fig. 3 is the matched filtering result that receives signal in Fig. 2.Although can find out and obtain 4 clearly target echoes, due to the attribute of not knowing that they are concrete, can only think that these may be all ship targets, caused very high false-alarm, in fact only having target 2 and target 4 is ship target echoes of motion.

Fig. 4 receives the matched filtering result of signal after Doppler shift in Fig. 2.Can find out that moving target 2 and moving target 4 have clearly obtained Echo Processing peak value, and static target 1 and 3 has been suppressed completely, so in this case, target 2 and the target 4 of motion will be presented on screen clearly.

From result, even under Low SNR, coding phase-modulated signal also has good performance on moving-target measuring ability as active signal, can shield the echo of static target, avoids the phenomenon of screen " babysbreath ".

Fig. 5 is under large signal to noise ratio (S/N ratio) condition, adopts the direct-wave jamming of coding phase-modulated signal to suppress result.The active signal that wherein direct wave sends for other ship, the target echo signal of the active signal that target echo sends for this ship, the code sequence of these two signals is different.The signal to noise ratio (S/N ratio) of target echo is 10.5 decibels.Large 60 decibels of direct wave energy Ratios target echo.Can find out, adopt after coding phase-modulated signal, can clearly obtain the peak value of target echo signal.

Fig. 6 is under little signal to noise ratio (S/N ratio) condition, adopts the direct-wave jamming of coding phase-modulated signal to suppress result.Other condition is identical during with large signal to noise ratio (S/N ratio), and just noise intensity increases, and makes the signal to noise ratio (S/N ratio) of target echo be-20.8 decibels, can find out, under little signal to noise ratio (S/N ratio) condition, adopts and encodes after phase-modulated signal, still can clearly obtain the peak value of target echo signal.

Generally speaking, adopt coding phase-modulated signal guaranteeing under the prerequisite of static target and moving object detection performance, effectively realize same direct-wave jamming frequently and suppress.

It should be noted last that, above embodiment is only unrestricted in order to technical scheme of the present invention to be described.Although the present invention is had been described in detail with reference to embodiment, those of ordinary skill in the art is to be understood that, technical scheme of the present invention is modified or is equal to replacement, do not depart from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of claim scope of the present invention.

Claims (4)

1. adopt coding phase-modulated signal to realize the method that direct-wave jamming suppresses, comprise

Centre frequency, bandwidth and the pulsewidth of step 1), definite coding phase-modulated signal;

Step 2), adjust coding form and the phase information of coding phase-modulated signal, generate all candidate transmitting signals, then calculate coefficient of autocorrelation, according to described coefficient of autocorrelation, described candidate transmitting signal is screened, obtain the preliminary set that transmits;

Step 3), for step 2) the preliminary set that transmits that obtains, calculate the their cross correlation between all signals in this set, according to described their cross correlation, described transmitting done to further screening, obtain the new set that transmits;

Step 4), calculation procedure 3) ambiguity function of signal in the set that transmits that obtains, by described ambiguity function, obtain doppler tolerance, then convert described doppler tolerance to theoretical rate accuracy, finally the theoretical rate accuracy of each signal and the permission speed of a ship or plane mobility scale of active sonar task object in the described set that transmits are compared, what in the set that transmits described in selecting according to comparative result, be applicable to transmits.

2. employing coding phase-modulated signal according to claim 1 is realized the method that direct-wave jamming suppresses, and it is characterized in that, in described step 2) in, the coding form of adjusting described coding phase-modulated signal comprises adjusts code element number and coded sequence.

3. employing coding phase-modulated signal according to claim 1 is realized the method that direct-wave jamming suppresses, and it is characterized in that, in described step 2) in, calculate coefficient of autocorrelation and comprise:

Step 2-1) signal, to each acquisition, calculates its coefficient of autocorrelation group, and computing formula is as follows:

Wherein, c _krepresenting the coefficient of autocorrelation that k kind is possible, k span is 1 ~ integer within (n-1); t _jrepresent a _jcorresponding phase information, and t _j+krepresent a _j+kcorresponding phase information; E and ∑ are the sign of operation of standard; A=[a ₁, a ₂..., a _n] be the sampled value of digital signal,

Step 2-2), from resulting coefficient of autocorrelation group, according to following formula, choose the coefficient of autocorrelation of maximum possible:

l=max{|c _k|:1≤k≤n-2}。

4. employing coding phase-modulated signal according to claim 1 is realized the method that direct-wave jamming suppresses, and it is characterized in that, in described step 3), calculates cross-correlation coefficient and comprises:

Two signals are A=[a ₁, a ₂..., a _n] and B=[b ₁, b ₂..., b _n], their cross correlation array expression formula is as follows:

Wherein

a _j, b _jrepresent respectively two signal sampling values, t _j, s _jrepresent respectively a _j, b _jcorresponding phase information;

From resulting cross correlation array, according to following formula, calculate the cross-correlation coefficient of maximum possible:

p=max{|c _k|:1≤k≤n-2}。

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