CN105068051A - Radar waveform amplitude and phase modulation method based on mixed sequences - Google Patents

Abstract

The invention discloses and relates to a radar waveform amplitude and phase modulation method based on mixed sequences and belongs to the field of radar transmitted waveform design. The method comprises steps of 1: obtaining to-be-modulated signals, judging periods requiring the signals, identifying numbers N of sub-pulse in one period where signals should be modulated, and mixing the tent sequence and the logistic sequence in proportion of 1:1 to obtain a mixed sequence with code length of N; using the mixed sequence in the step 2 to modulate phase positions of all pulse in the obtained periods; using the mixed sequence in the step 2 to modulate amplitude of the obtained modulated signals; and outputting modulation results. Combining advantages of amplitude modulation and phase modulation, signal amplitude and phase positions change along with chaotic signals, so complexity is increased and interception probability is reduced.

Description

A kind of radar waveform amplitude modulation and phase modulation method based on mixed sequence

Technical field

The invention belongs to radar emission waveform design field, relate to the method for the amplitude modulation and phase modulation of radar waveform.

Background technology

Radar emission signal waveform has extremely important impact to radar performance, transmits and determines the optimization process method of the system of radar, the generation of signal and Received signal strength.And the complexity of signal also ensure that the low interception capability of radar.In recent years, chaotic signal because having sharp-pointed autocorrelation function, the ambiguity function of drawing pin type, ultra broadband, just in time meets the requirement of the higher ranging and range rate precision of modern radar system; Meanwhile, the noise like characteristic of chaotic signal and initial value sensitivity make signal parameter not easily be intercepted and captured by enemy's melodeon, and chaotic modulation signal is deterministic signal concerning one's own side, for the design of one's own side's radar waveform is provided convenience.

It is more that chaos is used for Waveform Design achievement in amplitude, frequency, phase place separately modulation, but single modulation waveform complexity is lower, and limit the predictable probability of chaotic signal, the intercept probability (LIP) of radar and interference free performance (ECCM).Tent sequence and logistic sequence are the two kinds of chaotic signals relatively commonly used, and two kinds of sequences are in independent amplitude modulation, and phase modulation aspect has good auto-correlation and cross-correlation performance, but the poor performance of associating amplitude modulation and phase modulation.The multiplexed sequence that the present invention proposes to adopt tent sequence and logistic sequence to be mixed to form with 1:1 is for combining amplitude modulation and phase modulation waveform, reduce the predictable probability of chaotic signal, the intercept probability (LIP) of radar, improves interference free performance (ECCM).

Summary of the invention

The present invention is low mainly for there is waveform complexity based on the single amplitude modulation of chaos sequence or phase modulation Waveform Design, limit the predictable probability of chaotic signal, the problems such as the intercept probability (LIP) of radar and interference free performance (ECCM), and tent sequence and logistic sequence two kinds of sequences are in the problem of the poor performance of associating amplitude modulation and phase modulation.Propose adopt tent sequence and logistic sequence to be mixed to form with 1:1 multiplexed sequence for combining amplitude modulation and phase modulation waveform, be intended to the advantage in conjunction with amplitude modulation and phase modulation, signal amplitude and phase place all with chaotic signal change, improve complexity, reduce by intercept probability.

The technical solution adopted in the present invention is a kind of radar waveform amplitude modulation and phase modulation method based on mixed sequence, and the method comprises:

Step 1: obtain the signal needing modulation, judges the cycle needing this signal, identifies the subpulse number N needed in modulation signal one-period;

Step 2: tent sequence and logistic sequence 1:1 are mixed, obtaining code length is N mixed sequence;

Step 3: the mixed sequence using step 2, carries out phase-modulation to each pulse in the cycle obtained;

Step 4: the mixed sequence using step 2, carries out amplitude modulation(PAM) to the modulation signal that step 3 obtains;

Step 5: export modulation result.

First further described step 2 selects many group codes long is N mixed sequence, therefrom selects minimum one group of autocorrelation sidelobe as the follow-up mixed sequence carrying out modulating.

Further described step 3,4 equal time discretize after complex envelope expression formula be:

$S_{AM-PM}=\left\{\begin{array}{cc}x\left(n\right)\underset{n=0}{\overset{N-1}{\Σ}}{C}_l\left(n\right)V(n-{\mathrm{Kt}}_p)& ,n=1,\mathrm{2...},N\\ 0& ,else\end{array}\right.$

Wherein: x (n) is mixed sequence, $C_l\left(n\right)=\left\{\begin{array}{c}1,x\left(n\right)<E\\ -1,x\left(n\right)\&GreaterEqual;E\end{array}\right.,$ Wherein $E=\frac{1}{N}\underset{n=0}{\overset{N-1}{\&Sigma;}}x\left(n\right),$ V (t) is sub signal to be modulated, t _pfor subpulse width, and $V\left(t\right)=\left\{\begin{array}{cc}1/\sqrt{t_p}& ,0<t<t_p\\ 0& ,else\end{array}\right.,$ V (n-Kt _p) be a subpulse in signal one-period to be modulated.

The invention has the beneficial effects as follows: tent sequence and logistic sequence are used for associating amplitude modulation and phase modulation Waveform Design with the multiplexed sequence that 1:1 is mixed to form by the present invention, and multiplexed sequence inherently improves the complicacy of chaotic signal; Moreover amplitude and phase place, all with mixed sequence random variation, make signal greatly be reduced by the probability that enemy intercepts and captures, improve the stealth capabilities of radar system.Mixed sequence amplitude modulation and phase modulation radar waveform has sharp-pointed autocorrelation function, autocorrelation sidelobe peak maximum can reach-23.59dB, cross-correlation side lobe peak maximal value can reach-20.98dB, autocorrelation sidelobe peak average value-40.23dB, cross-correlation side lobe peak mean value can reach-39.89dB.Its ambiguity function has more satisfactory " drawing pin " shape, and significantly better than the situation of tent sequence association amplitude modulation and phase modulation or logistic sequence association amplitude modulation and phase modulation, performance can be equal in independent amplitude modulation, phase modulation with kind of the sequence of two in existing document.Than Tent sequence or Logistic sequence, tool in Amplitude-Phase combined modulation improves significantly visible mixed sequence.

Accompanying drawing explanation

Fig. 1 is tent sequence or logistic sequence Amplitude-Phase combined modulation signal picture group;

Fig. 2 is the oscillogram of above-mentioned mixed sequence;

Fig. 3 is the auto-correlation schematic diagram of mixed sequence Amplitude-Phase combined modulation chaos radar signal;

Fig. 4 is cross-correlation schematic diagram;

Fig. 5 is the emulation schematic diagram of ambiguity function.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

Suppose that MIMO radar system has M independently transmitter unit, and each transmitter unit is made up of N number of subpulse, sub-pulse duration is T.

Step 1: adopt Tent mapping and Logistic to map first respectively and generate two chaos sequences that length is N, then generate with 1:1 mixing the sequence that length is 2*N, be punctured into 2*N/P section sequence according to length P.The tent that employing is comparatively commonly used maps expression formula:

Chaos sequence in described step 1 adopts comparatively conventional tent to map expression formula:

x(n+1)＝0.5-u|x(n)|,n＝0,1,2......

X (0) is for initial value and x (0) ∈ [-0.5,0.5], x (n) ∈ [-0.5,0.5]; U is free parameter, and u=2-ε, ε → 0.Logistic maps expression formula:

x(n+1)＝u(0.25-x(n) ²)-0.5,n＝0,1,2......

X (0) is for initial value and x (0) ∈ [-0.5,0.5], x (n) ∈ [-0.5,0.5]; U is free parameter, and u=4-ε, ε → 0.ε gets 0.001, and initial value gets 0.39.

Step 2: choose one section of sequence, make its be x (0), x (1), x (2) ..., x (N) }; Choosing method is: emulate the 2*N/P section sequence in step 1, select one group that autocorrelation sidelobe is minimum.A large amount of emulation experiment shows, the Influence on test result chosen finally choosing of initial value is little.

Step 3: chaos associating amplitude modulation and phase modulation signal is encoded, coded system is about to a pulse and is divided into a series of subpulse, different amplitude modulation(PAM)s is carried out to different subpulses, in each amplitude coding subpulse, the random initial phase produced is used to each cycle of waveform simultaneously.

Step 4: Amplitude-Phase combined modulation chaos radar signal can be expressed as:

$u_{AM-PM}=\left\{\begin{array}{cc}kx\left(t\right)& ,0\&le;t\&le;T\\ 0& ,else\end{array}\right.$

Wide when in formula, T is chaotic signal modulation, k is amplitude modulation(PAM) coefficient, and x (n) is chaotic signal.

To u _aM-PMcarry out discretize

$u_{AM-PM}=\left\{\begin{array}{cc}kx\left(n\mathrm{\&Delta;}t\right)& ,0\&le;t\&le;T\\ 0& ,else\end{array}\right.$

Sample frequency must meet Nyquist criterion, can not aliasing.If k=1, then the complex envelope expression formula after equal time discretize is:

$S_{AM-PM}=\left\{\begin{array}{cc}x\left(n\right)\underset{n=0}{\overset{N-1}{\&Sigma;}}{C}_l\left(n\right)V\left(n-{\mathrm{Kt}}_p\right)& ,n=1,\mathrm{2...},N\\ 0& ,else\end{array}\right.$

Wherein x (n) is chaos sequence, and code length is N, and

V (t) is subpulse function, t _pfor subpulse width, and

$V\left(t\right)=\left\{\begin{array}{cc}1/\sqrt{t_p}& ,0<t<t_p\\ 0& ,else\end{array}\right.$

Step 5: chaos sequence has many-valued ergodicity, needs when phase encoding to quantize original chaos sequence two-value.The method that two-value quantizes is namely first ask the average of this original series, namely

$E=\frac{1}{N}\underset{n=0}{\overset{N-1}{\&Sigma;}}x\left(n\right)$

Then

$C_l\left(n\right)=\left\{\begin{array}{c}1,x\left(n\right)<E\\ -1,x\left(n\right)\&GreaterEqual;E\end{array}\right.$

Fig. 1 (a)-(c) is the auto-correlation of tent sequence (sequence length is 1024) Amplitude-Phase combined modulation chaos radar signal, the emulation schematic diagram of cross-correlation and ambiguity function; Fig. 1 (d)-(g) is the auto-correlation of logistic sequence (sequence length is 1024) Amplitude-Phase combined modulation chaos radar signal, the emulation schematic diagram of cross-correlation and ambiguity function, the auto-correlation that two kinds of sequences are modulated respectively can be found out, cross-correlation and ambiguity function not ideal, especially autocorrelation function secondary lobe is higher;

The auto-correlation schematic diagram that the oscillogram that Fig. 2 is above-mentioned mixed sequence, Fig. 3 are mixed sequence Amplitude-Phase combined modulation chaos radar signal, Fig. 4 are cross-correlation schematic diagram, and Fig. 5 is the emulation schematic diagram of ambiguity function.Design amplitude modulation(PAM) chaotic radar waveform and phase-modulation chaotic radar comparison of wave shape in a conventional method.Table 1 is tent sequence association amplitude modulation and phase modulation (AM-PM (tent)) normalized autocorrelation sidelobe peak maximum (maximum ASP), cross-correlation peak value maximal value (maximum CP), autocorrelation sidelobe peak average value (average A SP), cross-correlation peak value mean value (average CP); And logistic chaos sequence combines amplitude modulation and phase modulation (AM-PM (logistic)) normalized maximum ASP, maximum CP, average A SP, average CP; And mixed sequence combines amplitude modulation and phase modulation (AM-PM (comp)) normalized maximum ASP, maximum CP, average A SP, average CP.

The various modulation signal correlation analysis of table 1

Claims (3)

1., based on a radar waveform amplitude modulation and phase modulation method for mixed sequence, the method comprises:

Step 1: obtain the signal needing modulation, judges the cycle needing this signal, identifies the subpulse number N needed in modulation signal one-period;

Step 2: tent sequence and logistic sequence 1:1 are mixed, obtaining code length is N mixed sequence;

Step 3: the mixed sequence using step 2, carries out phase-modulation to each pulse in the cycle obtained;

Step 4: the mixed sequence using step 2, carries out amplitude modulation(PAM) to the modulation signal that step 3 obtains;

Step 5: export modulation result.

2. a kind of radar waveform amplitude modulation and phase modulation method based on mixed sequence as claimed in claim 1, it is characterized in that first described step 2 selects many group codes long is N mixed sequence, therefrom selects minimum one group of autocorrelation sidelobe as the follow-up mixed sequence carrying out modulating.

3. a kind of radar waveform amplitude modulation and phase modulation method based on mixed sequence as claimed in claim 1, it is characterized in that described step 3,4 equal time discretize after complex envelope expression formula be:

$S_{AM-PM}=\left\{\begin{array}{cc}x\left(n\right)\underset{n=0}{\overset{N-1}{\&Sigma;}}{C}_l\left(n\right)V(n-{\mathrm{Kt}}_p)& ,n=1,\mathrm{2...},N\\ 0& ,else\end{array}\right.$

Wherein: x (n) is mixed sequence, $C_l\left(n\right)=\{\begin{array}{c}1,x\left(n\right)<E\\ -1,x\left(n\right)\&GreaterEqual;E\end{array},$ Wherein v (t) is sub signal to be modulated, t _pfor subpulse width, and $V\left(t\right)=\left\{\begin{array}{cc}1/\sqrt{t_p}& ,0<t<t_p\\ 0& ,else\end{array}\right.,$ V (n-Kt _p) be a subpulse in signal one-period to be modulated.