CN101770023A - FM (Frequency Modulation) time frequency diversity signal processing method and system - Google Patents

Abstract

The invention relates to a processing method of active sonar FM (Frequency Modulation) time frequency diversity signals. The method can be used for the detection of underwater targets, greatly eliminate the modulating action of underwater acoustic channels and target reflection cross sections on signals and realize the steady detection of target echo signals. The invention also relates to a system capable of effectively realizing the processing method, and the system comprises an energy converter array, a pre-amplifier/filter circuit, an ADC (Analog to Digital Converter) circuit, a signal preprocessing module, a pulse-to-pulse correlator, a CFAR (Constant False Alarm Rate) processing module and a display module, wherein the energy converter array receives the target echo signal, and after the target echo signals pass through the pre-amplifier/filter circuit and the ADC circuit, digital signals are output and sent to the signal preprocessing module; the signal preprocessing module finishes signal demodulation and filtering and outputs a plurality of sequences to be subjected to pulse-to-pulse correlation processing; integrations after the pulse-to-pulse correlation processing are sent to the CFAR processing module, and the waviness of short range and long range target echoes is eliminated to realize the threshold detection of the target echoes; and the target echoes exceeding the threshold are sent to the display module.

Description

FM temporal frequency diversity signal disposal route and system

Technical field

The present invention relates to a kind of signal processing method of FM temporal frequency diversity signal, more particularly, relate to the method and system of relevant treatment between a kind of arteries and veins of active sonar FM signal.

Background technology

The waveform that active sonar is commonly used is Single Frequency C W signal and FM signal, and Single Frequency C W signal generally is used for the high-doppler target, has good frequency resolution, but the time resolution rate variance; And the FM signal generally is used for slower-velocity target, as LFM, and HFM and other frequency modulated signal; The FM signal bandwidth is big more, and anti-reverberation ability is strong more.Underwater acoustic channel is time, the decline of frequency bidimensional, and it has the decorrelation effect to same signal envelope on the different carrier frequency, and this effect is measured with coherence time and coherence bandwidth, general underwater acoustic channel 4s～24s coherence time, coherence bandwidth 300Hz; The coherence bandwidth of channel has limited the increase of FM signal bandwidth, but in order to improve rearmounted processing gain of sonar and anti-reverberation ability, often needs to increase bandwidth B again; Traditional sonar often adopts the bandwidth much larger than 300Hz in the FM signal; Signal frequency is high more, the easy more making of broadband underwater acoustic transducer, and bandwidth B is big more; Often neglect the influence of underwater acoustic channel environment in the rearmounted processing procedure to the FM broadband signal, this directly causes broadband FM echoed signal and emission to copy the mismatch of coherent signal, causes the active sonar performance sharply to descend.FM temporal frequency diversity signal is as a class FM signal, its yuan signal bandwidth can be reduced to 300Hz, satisfies the requirement of channel coherence bandwidth, but the conventional treatment method of this signal is matched filtering, owing to do not consider the factor of channel, still have the risk of SLM Signal Label Mismatch.

The modulating action that reduces channel is handled influence to the postposition of signal, can adopt based on a coupling processing (matched fieldprocessing, MFP) method, MFP by the basic matrix data that will receive with the source position parameter of supposition calculated expectation according to propagation model compare, determine the position in source; The modulating function of channel calculates acquisition by propagation model.The treatment effect of MFP depends on the accuracy of model, need have the parameter of underwater sound environment very accurately to understand, but present technical merit can't realize to environmental parameter on top of; MFP is the hot issue of underwater sound research at present, still has a segment distance from practical application; Admissible alternative approach is: eliminate the influence of underwater sound environment as far as possible.

Summary of the invention

In order to solve the difficult problem of FM signal environment mismatch, technical matters to be solved by this invention is the disposal route that proposes new FM temporal frequency diversity signal.This method is handled FM temporal frequency diversity signal based on treatment technology relevant between first signal arteries and veins, can greatly eliminate the influence of channel transfer functions and target reflection function, realizes the sane detection of target echo signal under the complex environment.Another technical matters to be solved by this invention is the disposal system that proposes effectively to realize above-mentioned disposal route.

The disposal route of the FM temporal frequency diversity signal that the present invention proposes may further comprise the steps:

(1) structure FM temporal frequency diversity signal

If FM unit signal is s (t), signal band [B ₀/ 2, B ₀/ 2], pulsewidth is T, and T generally selects several milliseconds to a few tens of milliseconds, and FM temporal frequency diversity signal is constructed by following formula

$r\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{s}_n\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}s(t-T_n)\exp (j.2\mathrm{\π}{f}_n.(t-T_n)),t\∈[\mathrm{nT},(n+1)T],$

$n=\mathrm{0,1},\·\·\·,N-1,---\left(1\right)$

N is first signal number, f _nBe carrier frequency, get carrier frequency f _nBetween difference frequency df=f _n-f _N-1Identical, and df＞=B, df=B selected herein; T _n=n*T, the express time retardation; s _n(t)=s (t-T _n) .exp (π f j.2 _n. (t-T _n)), t ∈ [nT, (n+1) T]; s _N+1(t) and s _n(t) life period relation

Formula (1) expression is modulated to different carrier frequency with same baseband signal s (t) at different time, can realize the temporal frequency diversity structure of FM signal;

(2) emission FM temporal frequency diversity signal r (t), and gather echo data, target echo signal be r ' (t), acquired signal is carried out Signal Pretreatment, finish signal demodulation and filtering, the multiple time series g (t) of output, comprise target echo signal r ' (t) among the g (t), but position the unknown;

(3) the multiple time series g (t) that step (2) is produced adopts relevant treatment between arteries and veins

Conjugate multiplication between the relevant treatment arteries and veins that to comprise twice interval time be T between arteries and veins, the T correspondence FM time-frequency diversity signal unit signal pulsewidth, conjugate multiplication between arteries and veins for the first time

c(t)＝g(t).conj(g(t+T))， (2)

Conj represents that plural number gets conjugation, and conjugate multiplication between arteries and veins still is T, promptly at interval for the second time

c ₀(t)＝c(t).conj(c(t+T))， (3)

To c ₀(t) the sliding window integration is adopted in output, and the sliding window width is (N-2) T

$I\left(t\right)={\∫}^{t+(N-2)T}{c}_0\left(\mathrm{\λ}\right)\mathrm{d\λ},t\≥0,---\left(4\right)$

I (t) is between arteries and veins the time series of relevant output, its peak correspondence (t) starting point of target echo signal r ';

(4) the wave beam time series I (t) that step (3) is produced asks absolute value abs (I (t)), carries out CFAR and handles, and can adopt logarithm CFAR detecting device, finishes all unit background estimating and thresholding and judges;

(5) target echo of judging through thresholding outputs to display device.

The disposal system of the FM temporal frequency diversity signal that the present invention proposes comprises transducer array, before put/filtering circuit, adc circuit, signal pre-processing module, relevant between arteries and veins, CFAR processing module and display module, transducer array receiving target echoed signal, through before putting/filtering circuit and adc circuit, the output digital signal, be sent to signal pre-processing module, Signal Pretreatment is finished signal demodulation and filtering, the output sequence of complex numbers, carry out relevant treatment between arteries and veins, the CFAR processing module is sent in integration output through relevant treatment between arteries and veins, eliminate the fluctuating of short range and remote object echo, realize the Threshold detection of target echo, and will cross the thresholding target echo and be sent to display module.

Preferably, put before the present invention is above-mentioned/filtering circuit also comprises the TVG gain adjusting circuit, be sent to adc circuit, realize the conversion of simulating signal to digital signal through the received signal of abundant amplification filtering.

With respect to prior art, the present invention has following beneficial effect:

1, the signal processing method of the present invention's proposition can greatly be eliminated the influence in underwater acoustic channel and target reflection cross section.

Underwater acoustic channel life period frequency two-dimensional undulation, establishing its modulating function is h ₁(t), corresponding spectrum H ₁(f), the target reflection function is h ₂(t), corresponding spectrum H ₂(f) since channel coherence time generally greater than 4s, can be under the situation about not changing in the target reflection cross section with Channel Modulation function h ₁(t) and target reflection function h ₂(t) be considered as the transport function of certain wave filter h (t), satisfy causality,

The r (t) that transmits is received by hydrophone array through wave filter h (t), and receiving echo g (t) can be expressed as

$g\left(t\right)=r\left(t\right)\⊗h\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{s}_n\left(t\right)\⊗h\left(t\right),---\left(5\right)$

Butt joint is regained ripple g (t) and is carried out relevant treatment between arteries and veins, and at first carrying out interval time is the time series conjugate multiplication of T, promptly

$c\left(t\right)=s_n\left(t\right)\⊗h\left(t\right).\mathrm{conj}(s_{n+1}\left(t\right)\⊗h\left(t\right))={\∫}_0^{\∞}{s}_n\left(\mathrm{\λ}\right).{s^{*}}_{n+1}\left(\mathrm{\λ}\right).{\left|h(t-\mathrm{\λ})\right|}^2.\mathrm{d\λ},$

$={\&Integral;}_0^{\&infin;}{\left|s_n\left(\mathrm{\&lambda;}\right)\right|}^2.{\left|h(t-\mathrm{\&lambda;})\right|}^2.e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H2008102051197E0000021.png,H2008102051197E0000031.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;B}(t-T_n)}\mathrm{d\&lambda;},$

$s_{n+1}\left(t\right)=s_n\left(t\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H2008102051197E0000021.png,H2008102051197E0000031.png"\; state="\{\{state\}\}">e</figure-callout>}}^j,t\&Element;[\mathrm{nT},(n+1)T],---\left(6\right)$

Between the visible arteries and veins of formula (6) conjugation as a result c (t) comprise time term

The influence of the modulating function h (t) that underwater sound environment is introduced only limits to amplitude modulation(PAM), and the phase modulation (PM) effect is cancelled; C (t) is carried out the conjugate multiplication of interval time T once more, promptly

$c_0\left(t\right)=c\left(t\right).\mathrm{conj}\left(c(t+T)\right)={\&Integral;}_0^{\&infin;}{\left|s_n\left(\mathrm{\&lambda;}\right)\right|}^2.{\left|h(t-\mathrm{\&lambda;})\right|}^2\mathrm{d\&lambda;}.{\&Integral;}_0^{\&infin;}{\left|s_{n+1}\left(\mathrm{\&lambda;}\right)\right|}^2.{\left|h(t+T-\mathrm{\&lambda;})\right|}^2\mathrm{d\&lambda;}.,---\left(7\right)$

c ₀(t) for just, do not contain complex item, intrinsic the differing that conjugation is introduced between arteries and veins is cancelled for the first time.

Derive as seen from formula (5), (6), (7), conjugate multiplication has been avoided the mismatch of conventional matching treatment between twice arteries and veins, and the modulating action that underwater sound environment is introduced is cancelled by Integral Processing, has environmental robustness.

2, the present invention make the FM signal can handle in the target of low speed, also can handle high-speed target.

The relevant treatment performance loss can minimize by following analysis between the arteries and veins of high-speed moving object: first signal s of formula (6), (7) _n(t) and s _N+1(t) simple crosscorrelation between is similar to matching treatment, can analyze according to blur level figure; Consider that FM time-frequency diversity signal is that LFM unit signal is filled, the signal pulsewidth T of unit, bandwidth B, establishing target speed is v, a certain direction target Equivalent scattering surface length is L, target Doppler 2v*f/c, the sustainable time of same cross section echo is L/v, then only need satisfy the adjacent different carrier frequency signal Doppler of unit difference less than first signal frequency resolution, and LFM signal frequency resolution is 0.44/T, be 2v*B/c＜0.44/T, the loss that can make the frequency mismatch introducing is less than 3dB; Unit's signal pulse compression or broadening amount should be less than first signal time resolution, and the LFM temporal resolution is 0.44/B, i.e. 2v*T/ (c+v)＜0.44/B can make loss that the time delay mismatch introduces less than 3dB; The total pulsewidth of signal should be less than equivalent object section life period, and promptly N.T＜L/v puts these restrictive conditions in order and obtains

BT＜0.22c/v，T＜L/(v.N)， (8)

As long as satisfy formula (8), then between FM time-frequency diversity signal arteries and veins the loss of relevant treatment less than 3dB.Other FM signal such as HFM, the restrictive condition of PR signal can be with reference to above-mentioned analysis.

3, the present invention is directed to FM temporal frequency diversity signal, Processing Structure is simple, has avoided the mismatch phenomenon of conventional matching treatment, can obtain the processing gain of 10log (N-2) * BT, has eliminated the uncertainty that environment is introduced, and has good robustness.

In a word, the present invention is by utilizing the characteristics of FM temporal frequency diversity signal structure, utilize between arteries and veins relevant dexterously, eliminate the modulating action in underwater acoustic channel and target reflection cross section, can realize the detection of target echo steadily, improved the detection performance of active sonar, had good environmental suitability, be applicable to that active sonar is to the detection of target under water.

Description of drawings

Fig. 1 is a FM time-frequency diversity signal system handles block diagram of the present invention;

Fig. 2 is a relevant treatment process flow diagram between arteries and veins of the present invention;

Fig. 3 is relevant treatment figure between FM time-frequency diversity signal arteries and veins of the present invention;

Fig. 4 is the comparison diagram of relevant treatment result between conventional matching treatment of FM time-frequency diversity signal of the present invention and arteries and veins.

Wherein:

100 is transducer array; 200 put/filtering circuit before being; 300 is adc circuit; 400 is signal pre-processing module; 500 is relevant between arteries and veins; 600 is the CFAR processing module; 700 is display module;

501 is that conjugation is taken advantage of I between arteries and veins; 502 is that conjugation is taken advantage of II between arteries and veins; 503 is Integral Processing;

801 is target echo; 802 is conjugate multiplication I between arteries and veins; 803 is conjugate multiplication II between arteries and veins; 804 is correlation integral output between arteries and veins; 901 is conventional matching treatment output.

Embodiment

Below in conjunction with the drawings and specific embodiments, further set forth the present invention.These embodiment are interpreted as only being used to the present invention is described and are not used in restriction protection scope of the present invention.After the content of having read the present invention's record, those skilled in the art can make various changes or modifications the present invention, and these equivalences change and modify and fall into claim of the present invention institute restricted portion equally.

As shown in Figure 1, the disposal system framework of the FM temporal frequency diversity signal that a preferred embodiment of the present invention provides can be with reference to figure 1, transducer array 100 receiving target echoed signals, FM temporal frequency diversity signal is filled first signal bandwidth and is got 300Hz, pulsewidth is selected several milliseconds to a few tens of milliseconds according to target speed, even longer; The output of transducer array 100 signals is through before putting/filtering circuit 200, and preceding putting/filtering circuit 200 also comprises the TVG gain adjusting circuit, and the received signal of the abundant amplification filtering of process is sent to adc circuit 300, realizes the conversion of simulating signal to digital signal.Adc circuit 300 will guarantee that but target echo is in its acquisition range, there is not amplitude limit in signal echo, this requires the TVG gain adjusting circuit to determine rational TVG control curve according to sound dissemination channel loss curve, emission source class, transducer sensitivity, the preceding enlargement factor etc. of putting, otherwise it is too weak and fully do not gathered to cause echoed signal excessively to be amplified amplitude limit or signal.Adc circuit 300 output digital signals are sent to signal pre-processing module 400, and signal pre-processing module 400 is finished signal demodulation and filtering, exports plural time series; Time domain or frequency-domain demodulation are adopted in the signal demodulation, eliminate carrier frequency information, obtain complex envelope output simultaneously, can realize down-sampledly, reduce data transfer rate.The 500 pairs of acquired signal of being correlated with between arteries and veins are carried out FM time-frequency diversity signal and are filled relevant treatment between the arteries and veins of first signal, eliminate these and fill phase time relation intrinsic between first signal, eliminate the influence of underwater acoustic channel transport function and target reflection function simultaneously, prerequisite is the influence that the design of signal can be avoided fast target, satisfy the stability requirement of underwater acoustic channel simultaneously, FM temporal frequency diversity signal length overall is generally less than 4s; Relevant 500 detailed process flow process is with reference to figure 2 between arteries and veins.Be sent to CFAR processing module 600 through relevant 500 signal amplitudes of handling between arteries and veins, employing based on logarithm CFAR detecting device more steadily estimated time cell background, and finish target detection, detection threshold is calculated by given false-alarm probability pfa and is obtained, and prerequisite supposition echo amplitude satisfies rayleigh distributed.Target echo through the CFAR detecting device is submitted display module 700 to, realizes the visual of target.

Fig. 2 is a dependence diagram between arteries and veins, be spaced apart the conjugate multiplication I 501 of T through the analytic signal of signal pre-processing module 400 outputs, conjugate multiplication II 502, T is first signal pulsewidth, conjugate multiplication I 501 finishes the functionalization of going of channel transfer functions and target reflection function, the synthesis result of channel transfer functions and target reflection function is to satisfy causal filter function in duration of pulse N*T, adjacent first signal carries out the conjugate multiplication I of interval T again by same filter function, will eliminate the influence of environmental information; Conjugate multiplication II 502 purposes are to eliminate the inconsistent intrinsic time phase term e that introduces of first signal carrier frequency information ^{-j2 π B}(t-T _n), be convenient to Integral Processing 503; Handle 503 through the signal input integral that conjugate multiplication I 501, conjugate multiplication II 502 handle, deadline length is the sliding window integration of (N-2) T, the output of picked up signal integration peak value, thereby the detectability of realization signal.The entire process process does not need conventional matching treatment.For noise or noise jamming, its structure no longer has the intrinsic result of FM temporal frequency diversity signal, the signal of interval time T is not to be modulated to different carrier frequency by same envelope signal, so conjugate multiplication I 501 is output as the random complex sequence, conjugate multiplication II 502 handles and also loses effect, the result is that the output of Integral Processing 503 integrations can not obtain the coherent integration result, and signal and noise are distinguished like this.

Fig. 3 is that array signal passes through after the Signal Pretreatment correlated process figure between certain wave beam arteries and veins, the lake examination data that adopt a linear array to gather, number of active lanes 32, the long 2.3m of battle array, sample frequency 50kHz, target is from receiving battle array apart from 515m, and about 97 ° in orientation is (with respect to the linear array direction, array element 1 to 32 direction is made as 180 °), corresponding echo signal appears at sampled point 34662; Wave beam is handled and is adopted 33 wave beams, is spacedly distributed corresponding 0 °～180 ° in the cosine space; Parameter transmits: first signal pulsewidth 2ms, first signal bandwidth 300Hz, 7 of first signal numbers, total pulsewidth 14ms.

Fig. 3 adopts staging treating, treated length 2048 points (, down-sampled) with respect to 8 times of crude sampling frequency 50kHz with respect to sampling rate 62500, and Signal Pretreatment comprises that signal demodulation and wave beam form, operations such as frequency domain filtering, signal is separated and is transferred to zero intermediate frequency; Indicate with block scheme the position that target echo signal occurs, and its wave beam orientation, place is 96.7 ° (corresponding No. 19 wave beams), and time location is a sampled point 383.From figure target echo 801 as seen, conjugate multiplication I802 between arteries and veins (handling according to formula (2)) is carried out in the serious distortion of signal, the transport function of underwater acoustic channel is eliminated the modulating action of signal phase, but still has the signal modulation intelligence; Carry out conjugate multiplication II 803 between arteries and veins (handling), signal bandwidth modulation proper phase e according to formula (3) ^{-j2 π B}(t-T _n) be eliminated, become the zero phase signal, this signal is carried out the sliding window integration (handling) of (7-2) * 2ms=10ms length according to formula (4), obtain correlation integral output 804 between arteries and veins, signal peak occurs, the modulating action of channel is exported by complete integral, has realized the inhibition of the coherent accumulation and the reverberation clutter of target echo.

Fig. 4 target echo signal 801 is through conventional matching treatment output 901, and the comparison of relevant treatment integration output 804 between arteries and veins, as seen from the figure, conventional matching treatment output 901 rises and falls very big, have mismatch, and ground unrest is big, and relevant treatment is exported between arteries and veins 804 smoother, background interference is low, has realized that the signal under the reverberation background strengthens and the clutter inhibition.

Claims (3)

1. the disposal route of a FM temporal frequency diversity signal is characterized in that, this method may further comprise the steps:

(1) structure FM temporal frequency diversity signal

If FM unit signal is s (t), signal band [B ₀/ 2, B ₀/ 2], pulsewidth is T, and T generally selects several milliseconds to a few tens of milliseconds, and FM temporal frequency diversity signal is constructed by following formula

$r\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{s}_n\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}s(t-T_n)\exp (j.2\mathrm{\&pi;}{f}_n.(t-T_n)),t\&Element;[\mathrm{nT},(n+1)T],$

n＝0，1，…，N-1， (1)

N is first signal number, f _nBe carrier frequency, get carrier frequency f _nBetween difference frequency df=f _n-f _n-1 is identical, and df＞=B, selects df=B herein; T _n=n*T, the express time retardation; s _n(t)=s (t-T _n) .exp (π f j.2 _n. (t-T _n)), t ∈ [nT, (n+1) T]; s _N+1(t) and s _n(t) life period relation

Formula (1) expression is modulated to different carrier frequency with same baseband signal s (t) at different time, can realize the temporal frequency diversity structure of FM signal;

(2) emission FM temporal frequency diversity signal r (t), and gather echo data, target echo signal be r ' (t), acquired signal is carried out Signal Pretreatment, finish signal demodulation and filtering, the multiple time series g (t) of output, comprise target echo signal r ' (t) among the g (t), but position the unknown;

(3) the multiple time series g (t) that step (2) is produced adopts relevant treatment between arteries and veins

Conjugate multiplication between the relevant treatment arteries and veins that to comprise twice interval time be T between arteries and veins, the T correspondence FM time-frequency diversity signal unit signal pulsewidth, conjugate multiplication between arteries and veins for the first time

c(t)＝g(t).conj(g(t+T))， (2)

Conj represents that plural number gets conjugation, and conjugate multiplication between arteries and veins still is T, promptly at interval for the second time

c ₀(t)＝c(t).conj(c(t+T))， (3)

To c ₀(t) the sliding window integration is adopted in output, and the sliding window width is (N-2) T

I(t)＝∫ ^t+(N-2)Tc ₀(λ)dλ，t≥0， (4)

I (t) is between arteries and veins the time series of relevant output, its peak correspondence (t) starting point of target echo signal r ';

(4) the wave beam time series I (t) that step (3) is produced asks absolute value abs (I (t)), carries out CFAR and handles, and can adopt logarithm CFAR detecting device, finishes all unit background estimating and thresholding and judges;

(5) target echo of judging through thresholding outputs to display device.

2. the disposal system of a FM temporal frequency diversity signal, it is characterized in that, this system comprises transducer array, before put/filtering circuit, adc circuit, signal pre-processing module, relevant between arteries and veins, CFAR processing module and display module, transducer array receiving target echoed signal, through before putting/filtering circuit and adc circuit, the output digital signal, be sent to signal pre-processing module, Signal Pretreatment is finished signal demodulation and filtering, the output sequence of complex numbers, carry out relevant treatment between arteries and veins, the CFAR processing module is sent in integration output through relevant treatment between arteries and veins, eliminate the fluctuating of short range and remote object echo, realize the Threshold detection of target echo, and will cross the thresholding target echo and be sent to display module.

3. the disposal system of FM temporal frequency diversity signal according to claim 2, it is characterized in that, before put/filtering circuit also comprises the TVG gain adjusting circuit, is sent to adc circuit through the received signal of abundant amplification filtering, realizes the conversion of simulating signal to digital signal.

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