CN104320243A - Analysis processing method of CD-FM-CDSK secret communication system - Google Patents

Abstract

The invention relates to an analysis processing method of a CD-FM-CDSK secret communication system, and belongs to the technical field of signal secret communications. The method comprises the following steps that (1) at a sending end, symmetric tent mapping is adopted to generate chaotic signals u(t), and signals which are output after FM are x(t); (2) in one symbol period, high-order signals and low-order signals are obtained after deserializing and then are modulated through chaotic signals which are subject to FM processing, and finally, modulated high-order signals and modulated low-order signals are summed and sent out together; (3) at a receiving end, correlation operation is conducted on received signals and delayed received signals, a relevant result is compared with a judgment threshold 0, and then the high-order signals and the low-order signals can be demodulated; (4) original signals are recovered through deserializing. According to the analysis processing method of the CD-FM-CDSK secret communication system, the transmission speed is two times that of a traditional CDSK, the signal bit energy of transmitted data signals is constant after FM, therefore, security is higher, cracking is not prone to occurring, and the BER performance is improved to some extent.

Description

A kind of analysis and processing method of CD-FM-CDSK secret signalling

Technical field

The invention belongs to signal security communication technical field, relate to a kind of analysis and processing method of CD-FM-CDSK secret signalling.

Background technology

In recent years, digital chaos encryption chip and encryption system research have made great progress.In digital secret communication system, system synchronization remains main research and the emphasis of product development, and wherein utilizing chaos system to realize actual time safety communication is the main target studied.In existing chaotic secret communication system, chaotic mask is applicable to analog signal and digital signal, chaotic parameter modulation and chaos shift keying (CSK) prevailing transmission digital signal.But for chaotic mask technology, when the amplitude of digital signal is greater than 5V, cover signal and will expose useful signal feature, therefore chaotic mask can only transmit little energy signal.In addition, due to chaotic mask mainly simple addition, multiplication and XOR, even if cover little energy signal, be also easily ravesdropping.Therefore, chaotic mask confidentiality is poor, and when chaotic mask communication system is subject to noise jamming, synchro system is easily lacked of proper care, and this affects the normal demodulation of useful signal.So chaotic mask Synchronization Secure system is difficult to be applicable to reality.The digital signal of transmission is hidden in system parameters by chaotic parameter modulation communication system, so its confidentiality is better than chaotic mask.But the same with chaotic mask technology, chaotic parameter modulation is also only applicable to the signal of slowly change, and can not process fast-changing signal and time varying signal very well, and Parameter Modulation disturbs extreme sensitivity to external world, these shortcomings reduce the efficiency of communication greatly.CSK is better than first two communication pattern in antinoise and parameter against sensitive ability, and overcomes the shortcoming that in chaotic mask, chaotic carrier power ratio available signal power is large.To sum up, CSK has stronger antijamming capability, good development prospect and actual application value, and this makes it in digital secret communication, have more researching value.

At present, the CSK technology main distinction be Synchronization of Chaotic Systems whether, namely receiver adopts coherent demodulation or non-coherent demodulation.Coherent demodulation need to set up one with the receiver of reflector Chaotic Synchronous, its confidentiality and antijamming capability better than non-coherent demodulation, be a kind of chaotic communication system with good development prospect.But when actual transmission channel signal to noise ratio is lower, be difficult to carry out Chaotic Synchronous coherent demodulation, so at present, most use non-coherent demodulation.Although the confidentiality of non-coherent demodulation is not high, its method is simple, and realization is easy and circuit is simple, reduces hardware cost.

CSK digital communication develops into difference CSK (DCSK), frequency modulation difference CSK (FM-DCSK), correlation delay keying (CDSK) and the orthogonal CSK (QCSK) etc. with better performance from initial chaotic modulating keying (COOK).Wherein, FM-DCSK relies on the superior function of its uniqueness to be listed in the long-term project of EU Committee.DCSK uses non-coherent approaches to carry out coherent detection, and due to characteristic aperiodic of chaotic signal, after DCSK modulation, bit energy can change according to the time.Therefore, the decision problem of receiver can be caused.The proposition of FM-DCSK well solves this problem.The modulator structure of FM-DCSK makes peace greatly DCSK unanimously, and just the chaotic signal advanced person of FM-DCSK crosses frequency modulation, and then modulates.Due to the relation constant (homophase or anti-phase) of chaos reference signal and information signal, so the demodulating process of FM-DCSK with DCSK is consistent, therefore FM-DCSK also has the shortcoming identical with DCSK, as lower message transmission rate and poor security performance.For improving bandwidth availability ratio, and sending signal continuously, introducing the modulation scheme of CDSK.Be replaced by adder at the transmitting terminal switch of CDSK, but delay time T need not equal T _b/ 2 (wherein, T _bbe the transmission time that bit needs), the transmitting terminal of this CDSK can continuous operation, and the chaotic signal of transmission does not repeat, and therefore effectively improves the confidentiality of system.

CDSK scheme is compared with traditional DCSK system, and difference is that the switch of DCSK system transmitting terminal is replaced by adder, and the signal obtained so more can transmit to continuous effective, and fail safe also improves a lot.That CDSK transmitting terminal output signal is chaotic signal and information signal and.The principles of modulation and demodulation figure of CDSK system as shown in Figure 1, 2.

Transmitting terminal output signal is:

s _i＝x _i+b _lx _i-L (1)

Wherein, x _ifor chaotic signal, b _lfor the digital signal of ± 1, L is for postponing length.

Be correlated with to received signal at receiving terminal, that is:

$\begin{array}{c}S=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{r}_i\·r_{i-L}\\ =\underset{i=1}{\overset{M}{\mathrm{\Σ}}}(s_i+{\mathrm{\ξ}}_i)(s_{i-L}+{\mathrm{\ξ}}_{i-L})\\ =\underset{i=1}{\overset{M}{\mathrm{\Σ}}}(x_i+b_l{x}_{i-L}+{\mathrm{\ξ}}_i)(x_{i-L}+b_{l-1}{x}_{i-2L}+{\mathrm{\ξ}}_{i-L})\\ =b_l\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{x}_{i-L}^2+\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\η}}_i\end{array}---\left(2\right)$

Wherein,

η _i＝x _ix _i-L+b _l-1x _ix _i-2L+b _lb _l-1x _i-Lx _i-2L+x _iξ _i-L+b _lx _i-Lξ _i-L+x _i-Lξ _i+b _l-1x _i-2Lξ _i+ξ _iξ _i-L (3)

Make S=b _la+b _lζ+η, wherein represent the information of carrying, the distracter caused by bit energy, be the distracter that interchannel noise produces, and average is 0.

Although the transmission rate of CDSK increases compared to DCSK, bit energy is still constant not.Therefore CDSK can not be applied to high-speed communication, and the proposition of FM-CDSK scheme solves the inconstant problem of bit energy.At transmitting terminal, chaotic signal, through analog-modulated, then carries out FM modulation, finally carries out digital modulation.The carrier signal energy obtained through FM is like this constant, and receiving terminal is the same with CDSK demodulation mode, the signal only needing simple treatment and analysis to receive, and utilizes correlation delay just can judge the signal sent.Do not need to rebuild chaotic carrier signal at receiving terminal, such receiving terminal more can facilitate and quick process information.The modulation principle figure of FM-CDSK system as shown in Figure 3.

For improving FM-CDSK message transmission rate further, the present invention, according to the deficiency of the current existing chaos shift keying communication technology, proposes a kind of novel chaos shift keying security scheme---CD-FM-CDSK (correlation delay-frequency modulation correlation delay keying).

Summary of the invention

In view of this, the object of the present invention is to provide a kind of analysis and processing method of CD-FM-CDSK secret signalling, the method not only transmission rate is 2 times of traditional C DSK, and the data-signal of transmission is after FM modulation, signal bit energy constant, therefore confidentiality is stronger, be not easily cracked, and error performance also increases.

For achieving the above object, the invention provides following technical scheme:

An analysis and processing method for CD-FM-CDSK secret signalling, comprises the following steps:

Step one: adopt symmetrical tent maps to produce chaotic signal u (t) at transmitting terminal, the signal of the output after FM modulates is x (t);

Step 2: in a symbol period, the high-low position signal obtained after serioparallel exchange, i.e. a and b.Then with the chaotic signal modulation after FM process, wherein high signal is modulated with the chaotic signal postponing τ/2, and low level signal is modulated with the chaotic signal postponing 3 τ/2.Eventually pass the later high-low position signal plus of modulation together to send;

Step 3: at receiving terminal, to received signal with postpone after Received signal strength carry out related operation, namely signal r (t) received is postponed τ/2 and 3 τ/2 respectively, and is correlated with respectively; Again correlated results and decision threshold 0 are compared, high-low-position signal can be demodulated;

Step 4: recover primary signal through parallel-serial conversion.

Beneficial effect of the present invention is: the program not only transmission rate is 2 times of traditional C DSK, and the data-signal of transmission is after FM modulation, and signal bit energy constant, therefore confidentiality is stronger, be not easily cracked, and error performance also increases.

Accompanying drawing explanation

In order to make object of the present invention, technical scheme and beneficial effect clearly, the invention provides following accompanying drawing and being described:

Fig. 1 is CDSK system modulation block diagram;

Fig. 2 is CDSK Demodulation Systems block diagram;

Fig. 3 is FM-CDSK system modulation block diagram;

Fig. 4 is the modulation principle figure of CD-FM-CDSK system;

Fig. 5 is the demodulation principle figure of CD-FM-CDSK system;

When Fig. 6 is M=8, the error performance of different technologies compares;

When Fig. 7 is M=16, the error performance of different technologies compares;

When Fig. 8 is M=24, the error performance of different technologies compares;

Fig. 9 is under different signal to noise ratio, the relation between M and BER;

Figure 10 is under different M value, E _b/ N ₀and the relation between BER;

Figure 11 is the schematic flow sheet of the method for the invention.

Embodiment

Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail.

Figure 11 is the schematic flow sheet of the method for the invention, as shown in the figure, method of the present invention specifically comprises: step one: adopt symmetrical tent maps to produce chaotic signal u (t) at transmitting terminal, the signal of the output after FM modulates is x (t); Step 2: in a symbol period, the high-low position signal obtained after serioparallel exchange, i.e. a and b.Then with the chaotic signal modulation after FM process, wherein high signal is modulated with the chaotic signal postponing τ/2, and low level signal is modulated with the chaotic signal postponing 3 τ/2.Eventually pass the later high-low position signal plus of modulation together to send; Step 3: at receiving terminal, to received signal with postpone after Received signal strength carry out related operation, namely signal r (t) received is postponed τ/2 and 3 τ/2 respectively, and is correlated with respectively; Again correlated results and decision threshold 0 are compared, high-low-position signal can be demodulated; Step 4: recover primary signal through parallel-serial conversion, completes the transmission of whole CD-FM-CDSK chaotic secret communication.

Specifically:

The concrete steps that the present invention realizes novel C D-FM-CDSK secret signalling are:

Step 1:

Chaos is prevalent in human society, and what mainly finger occurred in specific system seems random motion.This dynamical motion maintains the sensitiveness of height to initial condition.So just based on this chaology, it is almost impossible for wanting to carry out following prediction to system.Although chaos phenomenon is complicated, the non linear system producing chaos is but very simple, and wherein symmetrical tent maps is one of mapping of comparatively extensive use, and its expression formula is:

u _i+1＝1-D|u _i|，D＝2 (4)

Then chaotic signal u (t) utilizing above formula to produce obtains x (t) by FM modulation.

$\begin{array}{c}x\left(t\right)=A_m\cos \left(2\mathrm{\π}\right[\mathrm{ft}+m{\∫}_0^{t}u\left(\mathrm{\τ}\right)\mathrm{d\τ}]+\mathrm{\θ})\\ =A_m\cos (\mathrm{wt}+\mathrm{\α}\left(t\right)+\mathrm{\θ})\\ =A_m\cos {\mathrm{\φ}}_t\end{array}---\left(5\right)$

Wherein, A _mfor carrier amplitude, f represents carrier frequency, and m represents modulation factor, and θ represents initial phase.

Step 2:

As can be seen from accompanying drawing 4, information signal becomes two-way bipolar signal a and b through serioparallel exchange, then modulate with the chaotic signal after FM process respectively, wherein high signal is modulated with the chaotic signal postponing τ/2, and low level signal is modulated with the chaotic signal postponing 3 τ/2.Eventually pass the later high-low position signal plus of modulation together to send.Resultant signal expression formula after ovennodulation is:

s(t)＝x(t)+ax(t-τ/2)+bx(t-3τ/2) (6)

Wherein, x (t) is through FM and modulates later chaotic signal, and a, b are respectively the information signal after serial to parallel conversion, and x (t-τ/2), x (t-3 τ/2) are chaos inhibit signal.

Step 3:

Accompanying drawing 5 can be found out, after receiving terminal receives s (t), utilizes correlation reception to recover primary signal, at the correlation output of receiving terminal high signal is:

S _a＝∫r(t)·r(t-τ/2)dt

＝∫[x(t)+ax(t-τ/2)+bx(t-3τ/2)+ξ(t)]

·[x(t-τ/2)+ax(t-τ)+bx(t-2τ)+ξ(t-τ/2)]dt

＝a∫x ²(t-τ/2)dt+η _a (7)

Wherein, r (t) representative sends the signal obtained after signal s (t) mixes with noise ξ (t) in channel.

The correlation output in like manner obtaining low level signal is:

S _b＝∫r(t)·r(t-3τ/2)dt

＝∫[x(t)+ax(t-τ/2)+bx(t-3τ/2)+ξ(t)]

·[x(t-3τ/2)+ax(t-2τ)+bx(t-3τ)+ξ(t-3τ/2)]dt

＝b∫x ²(t-3τ/2)dt+η _b (8)

Wherein η _a, η _bthe product integral of the product integral of the product integral of 8 chaotic signals and chaos inhibit signal, 6 noises and chaotic signal, 1 noise and noise is all comprised inside expression formula.(4), in (5) formula Section 1 is carry information item, after be everyly interference.Can know by analyzing, after the integrated value of several be 0.

Step 4:

Decision threshold is set to 0, and receiving terminal only needs S _a, S _bcompare with decision threshold 0, high-low position signal can be demodulated, then can demodulate raw information through parallel-serial conversion.As shown in Figure 5.

$\left\{\begin{array}{cc}{Z}_a>0,& a=+1\\ Z_a<0,& a=-1\end{array}\right.$ Or $\left\{\begin{array}{cc}{Z}_b>0,& b=+1\\ Z_b<0,& b=-1\end{array}\right.---\left(9\right)$

So far complete in steps.

For CDSK system, A=E _b/ 2, represent signal energy.η represents noise, and ζ represents the information bit energy change caused after " chaos " spread spectrum and the estimation caused is disturbed.When N increases gradually, η ζ is tending towards Gaussian Profile gradually, needs the mean and variance determining η+ζ here.For any positive integer i, j, i ≠ j, ξ i, ξ j statistical iteration, N ₀be interchannel noise average power, can obtain obtain the average E [ζ η]=0 of η ζ thus.Because separate between η, ζ, thus the covariance between η, ζ is 0, simultaneously by the separate variance obtaining η+ζ of η, ζ ${\mathrm{\&sigma;}}_{\mathrm{\&zeta;}+\mathrm{\&eta;}}^2={\mathrm{\&sigma;}}_{\mathrm{\&zeta;}}^2+{\mathrm{\&sigma;}}_{\mathrm{\&eta;}}^2.$ The variance expression formula of η is: ${\mathrm{\&sigma;}}_{\mathrm{\&eta;}}^2=E_b{N}_0+\frac{{3E}_b^2}{4M}+\frac{N_0^{2}M}{4}.$ the variance that the bit energy caused by " chaos " changes the interference ζ caused, relevant to the chaotic maps type specifically adopted.Adopt symmetrical tent maps herein,

I.e. x _i+1=1-D|x _i|, wherein D=2.

Then ${\mathrm{\&sigma;}}_{\mathrm{\&zeta;}}^2=\frac{E_b^2}{5M},$ So ${{\mathrm{\&sigma;}}_{\mathrm{CDSK}}}^2={\mathrm{\&sigma;}}_{\mathrm{\&eta;}}^2+{\mathrm{\&sigma;}}_{\mathrm{\&zeta;}}^2=E_b{N}_0+\frac{{19E}_b^2}{20M}+\frac{N_0^{2}M}{4}.$

After adding FM modulator in CDSK secret signalling, change by information bit energy " chaos " estimation caused and disturb negligible,

Namely $\mathrm{\&zeta;}=\underset{i=1}{\overset{M}{\mathrm{\&Sigma;}}}{x}_{i-L}^2-A$ Negligible.

Thus obtain due at T _bin time, the information rate of the CD-FM-CDSK after serioparallel exchange becomes 2 times of FM-CDSK, but relevant time decision does not change, so the sequence length of CD-FM-CDSK correlation intergal becomes 2M.So can obtain:

${\mathrm{\&sigma;}}_{\mathrm{CD}-\mathrm{FM}-\mathrm{CDSK}}^2=E_b{N}_0+\frac{{3E}_b^2}{8M}+\frac{N_0^{2}M}{2}---\left(10\right)$

Therefore the error rate of novel C D-FM-CDSK is:

$\mathrm{BER}=\frac{1}{2}\mathrm{erfc}\left(\sqrt{\frac{E_b}{8N_0}{(1+\frac{3E_b}{8{\mathrm{MN}}_0}+\frac{M}{2}\frac{N_0}{E_b})}^{-1}}\right)---\left(11\right)$

Simulation result and performance evaluation: suppose that interchannel noise meets AWGN distribution.

Accompanying drawing 6,7,8 be respectively M=8,16, in 24 situations, three kinds of technology CDSK, FM-CDSK, CD-FM-CDSK bit error rate performances compare.Visible, when low signal-to-noise ratio, the bit error rate performance of three kinds of schemes is almost consistent, M=8,16,24 time, signal to noise ratio respectively 7.5,10, after 12.5dB the contrast of performance quality obvious gradually, can find out that CD-FM-CDSK is lower compared to other two technology error rates.In identical BER situation, the signal to noise ratio of three kinds of systems is also different, M=8, BER=10 ^-1, M=16, BER=10 ^-3/2, M=24, BER=10 ^-2time, CD-FM-CDSK system signal noise ratio raising more about than FM-CDSK 2.5dB.

Can be obtained by accompanying drawing 9, CD-FM-CDSK systematic function and M have very large relation, when M within the specific limits time, with M increase, error rate of system reduce, systematic function is better.Work as E _b/ N ₀during < 10dB, the size of M is little to systematic influence.As 10dB < E _b/ N ₀during < 30dB, system error performance has greatly improved, at E _b/ N ₀when about 30dB, nearly 1/2 order of magnitude of improvement in performance.Work as E _b/ N ₀during > 30dB, systematic function almost remains unchanged.

Can find out in accompanying drawing 9, error rate of system is not ever-reduced along with the increase of M value.The increase of M in certain span can make systematic function continue to optimize, but when M get continue to increase M after a certain extreme value time, systematic function there will be deterioration on the contrary, and signal to noise ratio is larger, then the extreme value that can get of M is larger.As figure, at E _b/ N ₀when being 5,10,15,20,25, corresponding M extreme value is respectively 4,8,13,18,23.Although M value is larger in certain limit, corresponding BER is less, and the increase of M also can cause the rate of information throughput of system to reduce, so suitable M value of choosing also is necessary, Figure 10 is under different M value, E _b/ N ₀and the relation between BER.

What finally illustrate is, above preferred embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although by above preferred embodiment to invention has been detailed description, but those skilled in the art are to be understood that, various change can be made to it in the form and details, and not depart from claims of the present invention limited range.

Claims (1)

1. an analysis and processing method for CD-FM-CDSK secret signalling, is characterized in that: comprise the following steps:

Step one: the chaos generator adopted at transmitting terminal is symmetrical tent maps, and the signal generated is modulated through FM, and the signal after modulation is x (t);

Step 2: needing the information of transmission first through serioparallel exchange, become high-low-position signal a and b; Chaotic signal x (t-τ/2) respectively with two-way after τ/2 postpone with 3 τ/2 is multiplied with x (t-3 τ/2), exports to obtain s (t)=x (t)+ax (t-τ/2)+bx (t-3 τ/2) together with being then added with chaotic signal by modulated high-low-position signal;

Step 3: at receiving terminal, to received signal with postpone after Received signal strength carry out related operation, namely signal r (t) received is postponed τ/2 and 3 τ/2 respectively, and is correlated with respectively; Again correlated results and decision threshold 0 are compared, high-low-position signal can be demodulated;

Step 4: recover primary signal through parallel-serial conversion.