CN103905358A

CN103905358A - Improved type differential chaos shift keying DCSK confidentiality communication method

Info

Publication number: CN103905358A
Application number: CN201410085985.2A
Authority: CN
Inventors: 张刚; 王源; 张天骐; 贺利芳; 李波; 王颖
Original assignee: Chongqing University of Post and Telecommunications
Current assignee: Chongqing University of Post and Telecommunications
Priority date: 2014-03-10
Filing date: 2014-03-10
Publication date: 2014-07-02

Abstract

The invention discloses a confidentiality communication method based on an improved type DCSK, and belongs to the technical field of signal transmission. In response to the confidentiality problem of the DCSK, after the improvement, information is scattered to two communication channels to be transmitted, a reference signal of the information in each channel is transmitted in the other channel, so that even the information in one channel is intercepted and captured in the transmission process, the original signal cannot be decoded, and the problem of low channel utilization rate is solved. Through the comparison of the original system bit error rate with the improved system bit error rate, the bit error rate of the improved type DCSK system is lower than the bit error rate of the traditional system in the data transmission process, and the channel utilization rate is much higher and confidentiality is much stronger. Through simulation it can be seen that the simulation result is consistent with the theoretical analysis, and confidentiality is greatly enhanced. Meanwhile, the improved type differential chaos shift keying DCSK confidentiality communication method is relatively low in complexity, easy for the project to be realized, and will has wide application prospect in the fields of images, military confidential information and the like.

Description

Improved differential chaos keying DCSK secret communication method

Technical Field

The present invention relates to data communication systems, and more particularly, to a chaotic secure communication method for transmitting and receiving data using improved differential chaotic keying.

Background

Since 1990, chaotic communication and chaotic synchronization technology have become a research hotspot for international and domestic communication. The development of the chaos synchronization control theory lays a theoretical foundation for the application of chaos in the communication field. The utilization of synchronous chaos for secret communication is a major international research hotspot. The synchronous chaotic communication that has been proposed and developed so far is mainly classified into: chaos masking, chaos parameter modulation, chaos keying and chaos spreading. Chaos covering belongs to chaos analog communication, and the other three types belong to chaos digital communication. Chaos covering is a chaos secret communication mode which is proposed earlier, a transmission signal covered under a chaos signal is extracted by utilizing a nonlinear dynamics prediction technology, the realization of the chaos signal depends on the synchronous realization degree of a system, therefore, high-quality communication service cannot be provided, the chaos signal covering method is only suitable for a slow-varying signal, and the chaos signal and a time-varying signal cannot be well processed. The chaos parameter modulation is to hide the transmitted information in the system parameter, the key of the scheme lies in the recovery degree of the chaos system parameter, and the demodulation of the system parameter is sensitive to the external interference, thereby reducing the communication efficiency. The chaotic spread spectrum communication is to replace a pseudo-random sequence of a traditional communication system by a chaotic sequence, thereby meeting the higher requirements of people on future communication. Due to some characteristics of the chaotic signal, the chaotic spread spectrum sequence has good random performance, high confidentiality, good correlation characteristics and a large number of usable signals. The key of chaotic spread spectrum communication lies in the selection of chaotic spread spectrum sequences, and the research on the chaotic sequences is also an important aspect of the research on chaotic communication at present. Chaos keying is that there are several chaos systems at the sending end, and different chaos systems are gated according to the code value to be transmitted. Thus, the sending signal is composed of a section of chaotic signal representing different chaotic attractors, and each chaotic system of the sending end is provided with a corresponding synchronous system at the receiving end. The received signal drives each synchronous system, and the code value transmitted in one code element period is judged according to the condition that each synchronous system achieves synchronization in the period. In the chaotic digital communication system, the chaotic keying has strong anti-jamming capability, can effectively inhibit the influence of multipath interference on the system, plays an important role in a communication scheme, and is considered by broad scholars to have better development prospect and application value. The chaos keying modulation technology has strong anti-noise interference and parameter mismatch capability and low power spectral density, so the chaos keying modulation technology is widely applied to a digital secret communication system. The technique of Chaos Shift Keying (CSK), chaos on-off keying (COOK), differential chaos keying (DCSK), frequency modulation differential chaos keying (FM-DCSK) and the like are derived based on the Chaos Shift Keying (CSK), the chaos on-off keying (COOK), the differential chaos keying (DCSK), the frequency modulation differential chaos keying (FM-DCSK) and the like. The CSK and COOK technologies enable the threshold judgment of the system receiving end to be changed according to the change of the signal-to-noise ratio, otherwise the system has higher bit error rate to cause the performance of the system to be reduced. To solve the problem, g.kolomban et al also propose differential chaos keying (DCSK) based on incoherent demodulation, which overcomes the disadvantage that the decision threshold values of CSK and COOK depend on the signal-to-noise ratio, and meanwhile, the receiving end does not need synchronization, and the structure is simple but on the premise. The specific inherent broadband characteristic of FM-DCSK adopts the method of firstly carrying out frequency modulation on chaotic signals so as to keep the signal energy constant, but therefore, an analog phase-locked loop (APLL) and an FM modulator need to be added at the sending end of FM-DCSK, and the circuit is complicated.

The output signal of the differential chaos keying (DCSK) has inherent broadband characteristic and anti-noise characteristic, and because the non-coherent demodulation technology is adopted, synchronization does not need to be established at the transmitting end and the receiving end, so that the DCSK has many advantages compared with the traditional communication system. But its transmission rate is low and its security is poor.

Disclosure of Invention

In view of the above deficiencies in the prior art, the present invention aims to provide an improved DCSK secure communication method with improved transmission rate, improved security, less possibility of being cracked, improved error code performance, and improved utilization rate. The technical scheme of the invention is as follows:

an improved differential chaos keying DCSK secret communication method comprises the following steps:

101. generating two different chaotic signals by adopting Logistic chaotic mapping generator at transmitting end of chaotic systemAnd chaotic signal

And will chaos signal

And chaotic signal

Respectively obtaining delayed chaotic signals after the phase delay of a spread spectrum coefficient M

And delaying the chaotic signal

102. Message to be sent

After serial/parallel conversion, the signals are divided into two paths of sequences a and b with half-reduced speed, and then the two paths of sequences are converted into two paths of bipolar signals through level conversion

And

and will bipolar signal

And the delayed chaotic signal obtained in the step 101Multiplying to obtain a transmission signalPut in channel I for transmission, the bipolar signal

And the delayed chaotic signal obtained in the step 101

Multiplying to obtain a transmission signal

Placed in channel II for transmission, the output signal of channel I being

The output signal of the channel II is

In which the channel I is in the first half of a symbol period T

The channel transmits a reference signal, andthe second halfThe periodic channel transmitting a transmission signal

First half period of channel IIThe channel transmits the reference signal, and the second halfThe channel transmitting signals in a cycle

103. When the output signal of channel I in step 102

Output signal of channel II

After the signals are transmitted to a receiving end of the chaotic system, the receiving end decodes the received signals to recover r1, n and r2, n;

104. decoding the recovered signal r in step 103_1,nAnd r_2,nBy autocorrelation of a correlator, i.e. by applying a received signal r_1,nAnd r_2,nThe signal r (n + M) with M bits delayed in the same time is subjected to correlation operation in the interval of the spreading factor M to obtain y_1,kAnd y_2,k；

105. And (5) changing the signals y1, k and y2, k after the autocorrelation operation in the step 104 into serial transmission from parallel transmission, and completing the data transmission of the secure communication.

Further, the expression of Logistic chaotic mapping generator in step 101 is

Where x (n) is a chaotic signal and μ is a coefficient.

Further, the Logistic chaotic map generator generates chaotic signals when μ =2.9 and μ =3.0And chaotic signal

Further, the expression of the autocorrelation in step 104 is

Where r (n) represents the received signal, r (n) includes r_1,nAnd r_2,nAnd r (n + M) represents a signal delayed by M bits, M being a spreading factor.

The invention has the following advantages and beneficial effects:

aiming at the defects of the prior art on chaos keying communication, the invention provides an improved DCSK

The system, the output signal of the differential chaos keying (DCSK) has the inherent wide-band characteristic and the anti-noise characteristic

And the method adopts the non-coherent demodulation technology, so that the synchronization does not need to be established at the transmitting end and the receiving end, compared with the traditional communication

The system has many advantages. But its transmission rate is low and its security is poor. Aiming at the problems, the invention provides a

An improved DCSK secret communication system not only ensures the transmission rate but also improves the security

The confidentiality is greatly enhanced, the data is not easy to crack, the error code performance is improved, and the profit is improved

And (7) the rate.

Drawings

FIG. 1 is a modulation schematic diagram of a DCSK system in accordance with a preferred embodiment of the present invention;

FIG. 2 is a demodulation schematic diagram of a DCSK system;

FIG. 3 is a schematic diagram of a modified DCSK modulation;

FIG. 4 is a schematic diagram of an improved DCSK demodulation;

FIG. 5 is a sequence diagram of an improved DCSK accept message exchange;

FIG. 6 is a bit error rate comparison of a conventional DCSK and a modified DCSK;

FIG. 7 is a diagram of the bit error rate of the modified DCSK with different M values;

FIG. 8 modified DCSK difference

And (4) lowering the error rate.

Detailed Description

The invention will now be further elucidated with reference to the following non-limiting embodiment in which the drawing is combined.

DCSK is the chaos keying secret communication system that studies the most at present, and system simple structure, the bit error rate is lower, and the interference killing feature is stronger, but has a problem in practical application: in a code element period, a reference signal and an information signal sent by a sending end are the same or opposite, so the channel confidentiality is lower, the sent information is intercepted and then is easy to decipher a transmission signal through analysis, and only 1bit of information can be transmitted in one period, so that the channel utilization rate and the transmission speed are lower. Aiming at the confidentiality problem of DCSK, the information is transmitted on two channels in a dispersed way through improvement, and the reference signal of each channel of information is transmitted on the other channel, so that even if a certain channel of information is intercepted in the transmission process, the original signal cannot be decoded, and the problem of low channel utilization rate is solved.

In 1996, g.kolomban proposed a differential chaos keying scheme (DCSK) to solve the problem that the CSK decision threshold value depends on the signal-to-noise ratio. In the DCSK scheme, each bit of information is converted and composed of two sections of chaotic signals, wherein the first section is a reference signal, the second section carries useful information, when the transmission information is 1, two sections of identical in-phase signals are transmitted, and when the transmission information is 0, two sections of signals at a transmitting end are in phase reversal, namely, a section of signals in phase reversal with the reference signal is behind the reference signal, and the two sections of signals are continuously transmitted. After receiving the information signal and the reference signal at the receiving end, sending the information signal and the reference signal to a related receiver, calculating the related characteristics of the two sections of signals, and recovering the information according to the positive and negative of the related characteristics, wherein if the related characteristics are greater than zero, the information signal is '1', and if the related characteristics are less than zero, the information signal is '0'. Modem demodulation principle of DCSK system

The figures are shown in figures 1 and 2.

Each bit of information of a DCSK system sending end consists of two sections of chaotic signals with the same length, wherein the former section transmits a reference signal, and the latter section transmits an information signal. Firstly, converting an original binary signal into a bipolar signal through a converter, then sending out M chaotic signals as reference signals in the former T/2, and sending out the M reference signals after delaying M bits in the latter T/2 and modulating the M reference signals with the bipolar signal. Wherein, if the transmitted signal is "+ 1", the information signal is the same as the reference signal; if the transmitted signal is "-1", the information signal is equal to the inverted reference signal. Therefore, the output signal s (n) of the transmitting end can be expressed as:

where x (n) is a chaotic signal, b (k) is a bipolar signal, and M is a spreading factor. At the receiving end, the correlation operation is performed on the reference signal and the information signal, that is, the correlation operation is performed on the received signal r (n) and the signal r (n + M) with M bit delay in the interval of the spreading factor M. The output formula of the correlator is as follows:

assume that the received signal is r (n) = s (n) + ξ (n), where ξ (n) is the channel noise. If the receiver has acquired synchronization, the correlator output is as shown in equation (3):

in equation (3), the first term is the useful signal and the second term is random noise with a mean value of zero. It can be seen that y (k) is consistent with the polarity of the bipolar signal b (k), so that the original signal can be demodulated, i.e., the original signal

The system changes the traditional single-channel transmission mode into the mode of dispersing information into two channels for transmission. In the DCSK scheme proposed by g.kolomban et al, each bit of information at the system transmitting end consists of two segments of chaotic signals with the same length, the former segment transmits a reference signal, and the latter segment transmits an information signal. After interception, by observing the frequency spectrum of the transmission signal, the rule can be easily found, and the original information is easy to be cracked, so that the method is difficult to have better confidentiality. Moreover, each bit of information can only transmit one binary bit, and the information transmission efficiency is low. In view of the above situation, an improved DCSK system is provided, which has greatly enhanced security, is not easy to be cracked, has improved error code performance, and has improved utilization rate.

By combining the examples, the specific steps for realizing the improved DCSK secure communication system of the invention are as follows:

step 1:

chaos theory begins to be applied to secure communication, wherein most of the theory is to use a Logistic system to generate a pseudo-random number sequence, and the theoretical basis is the sensitivity of a chaotic power system to initial values and parameters. However, Logistic systems are chaotic only when the initial values and parameters take values within certain specified ranges, and are not chaotic for any initial values and parameters. Secondly, even if the Logistic system is in a chaotic state, the randomness of the pseudo-random sequences generated under different initial values and parameters is greatly different. The present invention considers the Logistic system expression to have the following form:

when different initial values are adopted, the generated chaotic signals are different. Input signal

Modulated and thus the characteristics of the modulation system are altered by the input signal. For example, when the input signal is changed from cosine wave to rectangular wave, the system is not a chaotic system. Therefore, for security purposes, the modulated signal is to be retained

The chaotic nature of (1). As used herein

Two values of (a) produce two different chaotic signals.

Step 2:

in the traditional DCSK transmission scheme, a reference signal and a modulation signal are transmitted on the same channel, and transmitted information is intercepted and then is easily decoded through analysis. The improved DCSK introduces a channel based on the original DCSK. As can be seen from the transmitting end of FIG. 3, the information

Firstly, the signals are converted into two paths of bipolar signals through serial-parallel conversion

Andthen respectively delaying two different chaotic signals with two paths of signals after M delay

And

multiplying to obtain a signal

And, separately, put into two channels for transmission, so thatThe respective reference signal and the modulation signal are separated and transmitted in different channels. Due to the special orthogonality of the chaotic signals, the signals in the two transmission channels are orthogonal. The sequence of the demodulation mode information in one symbol period T is simplified as shown in fig. 2. Information is dispersed on two channels in the transmission process, the frequency spectrum is greatly expanded, and the confidentiality is greatly enhanced. Even if the listener intercepts

Or

The sequence cannot be deciphered, and thus, complete secure communication can be achieved. Two channel output signal

And

respectively shown in formulas (6) and (7):

<math> <mfenced open='' close=''> <mtable> <mtr> <mtd> <msub> <mi>s</mi> <mrow> <mn>1</mn> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>=</mo> <munderover> <mi>Σ</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>0</mn> </mrow> <mo>∞</mo> </munderover> <mo>[</mo> <msub> <mi>x</mi> <mrow> <mn>1</mn> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>·</mo> <msub> <mi>R</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>2</mn> <mi>jM</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>b</mi> <mrow> <mn>2</mn> <mo>,</mo> <mi>k</mi> </mrow> </msub> <msub> <mi>x</mi> <mrow> <mn>2</mn> <mo>,</mo> <mi>n</mi> <mo>-</mo> <mi>M</mi> </mrow> </msub> <mo>·</mo> <msub> <mi>R</mi> <mrow> <mi>N</mi> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mi>j</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mi>M</mi> </mrow> </msub> <mo>]</mo> </mtd> <mtd> <mo>&ForAll;</mo> <mi>j</mi> <mo>&Element;</mo> <mi>N</mi> </mtd> </mtr> </mtable> <mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow> </mfenced> </math>

<math> <mrow> <msub> <mi>s</mi> <mrow> <mn>2</mn> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>=</mo> <mfenced open='' close='-'> <mtable> <mtr> <mtd> <munderover> <mi>Σ</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>0</mn> </mrow> <mo>∞</mo> </munderover> <mo>[</mo> <msub> <mi>x</mi> <mrow> <mn>2</mn> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>·</mo> <msub> <mi>R</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>2</mn> <mi>jM</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>b</mi> <mrow> <mn>1</mn> <mo>,</mo> <mi>k</mi> </mrow> </msub> <msub> <mi>x</mi> <mrow> <mn>1</mn> <mo>,</mo> <mi>n</mi> <mo>-</mo> <mi>M</mi> </mrow> </msub> <mo>·</mo> <msub> <mi>R</mi> <mrow> <mi>n</mi> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mi>j</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mi>M</mi> </mrow> </msub> <mo>]</mo> </mtd> <mtd> <mo>&ForAll;</mo> <mi>j</mi> <mo>&Element;</mo> <mi>N</mi> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>7</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein,and

is a chaotic signal and is a signal that is,

and

is a bipolar signal, Rn represents a gate function with the length of M, and M is a spreading coefficient, namely each symbol is modulated by an M bit chaotic signal. The relationship between the information rate and the rates of the two signals and the final modulated information rate is shown in (8), where rs, rk and ri respectively represent the channel rate, the transform rate and the information rate.

rs=2Mrk=Mri(8)

In one symbol period T, (6) (7) can be simplified to (9) (10), wherein the first half period

The channel transmits the reference signal, and the second half

The periodic channel transmits the other path of modulation signal. The problem that if one channel is intercepted, the information can be cracked is avoided.

And step 3:

as can be seen in figure 4 of the drawings,

and

after being transmitted to the receiving end at the same time, beforeGet

And

front M bits and rear

Get

And

then M bits and the channel is switched so that the scrambled order is restored again at the transmitting end. The exchange mode is adopted to avoid the weakness that a certain path of information is intercepted in the transmission process and the original signal is decoded, and simultaneously, the problem of low channel utilization rate is solved. The exchanged signals are, as can be seen from fig. 4, respectively, so that the disorderly sequence before transmission is adjusted back at the receiving end, as shown in equations (11) (12):

r_{3, n} = \{\begin{matrix} x_{1, n} & 0 < t < T / 2 \\ b_{1, k} X_{1, n - M} & T / 2 < t < T \end{matrix} - - - (11)

r_{4, n} = {\begin{matrix} x_{2, n} & 0 < t < T / 2 \\ b_{2, k} x_{2, n - M} & T / 2 < t < T \end{matrix} - - - (12)

and 4, step 4:

after the receiving end readjusts the sequence, the two paths of signals respectively perform autocorrelation operation, as shown in fig. 5.

Suppose that two signals received at the receiving end are r_1,n=s_1,n+ξ_1,n，r_2,n=s_2,n+ξ_2,nIn which ξ_1,nξ 2, n denotes Additive White Gaussian Noise (AWGN) with a mean value of 0, σ₁ ²Is xi_1,nVariance of (a)₂ ²Is xi_2,nThe variance of (c). And when i ≠ j,

and xi_2,nAnd (4) performing statistical independence. The sequence after the two paths of merging is as follows:

then, the output of the first path correlator is as shown in equation (15):

first term of formula (15)

Is the desired useful signal, the second term

Is a random quantity with a mean value of zero, then y_1,kAnd b_1,kB is consistent, then b can be judged_1,kAs shown in equation (16):

the same can derive (17) (18) two formulas:

b_{1, k} = \{\begin{matrix} 1 & y_{1, k} > 0 \\ 0 & y_{1, k} < 0 \end{matrix} - - - (16)

b_{2, k} = {\begin{matrix} 1 & y_{2, k} > 0 \\ 0 & y_{2, k} < 0 \end{matrix} - - - (18)

step 5

The two channels are recoded after autocorrelation and are reordered to restore data after parallel-serial conversion. As shown in fig. 5.

All steps are completed.

The code error performance and the spread spectrum coefficient M of the modulation and demodulation mode and

the relationship is close. Comparing with the traditional modulation mode, analyzing the probability of P (0|1) in the first channel, namely the error probability of judging that the transmission ' 1 ' is ' 0 ', and assuming b '_1,K=1, equation (15) becomes (19),

for the energy of the signal in T/2 time

Equation (20) can be written as:

the left side of the formula (20) is a random process

(i, j) condition, x_i,n，ξ_i,nIndependent of each other and

has a mean value of 0 and is in any caseXi ≠ j condition_i,nAnd xi_j,nIs statistically independent, σ² ₁Is xi₁Of

Difference, σ² ₂Is xi₂Variance of, N₁、N₂Noise mean power spectral density of the two channels, respectively, and thus

The left-hand mean μ = E (β) =0 of the above formula, variance is:

in chaotic systems, the chaotic signal x_i,nAnd x_i,n+MThe correlation between them decays rapidly as M increases. Assuming that M is greater than the correlation feature decay time, β approaches a gaussian distribution as M increases. Therefore, the formula for improving the bit error rate of the DCSK system can be written as formula (22). Where erfc (x) is a complementary error function, i.e.

<math> <mrow> <mi>erfc</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>2</mn> <msqrt> <mi>π</mi> </msqrt> </mfrac> <msubsup> <mo>&Integral;</mo> <mi>x</mi> <mo>∞</mo> </msubsup> <mn>2</mn> <mi>xp</mi> <mrow> <mo>(</mo> <msup> <mrow> <mo>-</mo> <mi>t</mi> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mi>dt</mi> </mrow> </math>

<math> <mfenced open='' close='' separators='-'> <mtable> <mtr> <mtd> <mi>BER</mi> <mo>=</mo> <mi>P</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo><</mo> <mo>-</mo> <mfrac> <msub> <mi>E</mi> <mi>b</mi> </msub> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mo>=</mo> <mfrac> <mn>1</mn> <msqrt> <mn>2</mn> <mi>πσ</mi> </msqrt> </mfrac> <msubsup> <mo>&Integral;</mo> <mrow> <mo>-</mo> <mo>∞</mo> </mrow> <mrow> <mo>-</mo> <mfrac> <msub> <mi>E</mi> <mi>b</mi> </msub> <mn>2</mn> </mfrac> </mrow> </msubsup> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mfrac> <msup> <mi>β</mi> <mn>2</mn> </msup> <msup> <mrow> <mn>2</mn> <mi>σ</mi> </mrow> <mn>2</mn> </msup> </mfrac> </mrow> </msup> <mi>dβ</mi> </mtd> </mtr> <mtr> <mtd> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mi>erfc</mi> <mrow> <mo>(</mo> <mfrac> <msub> <mi>E</mi> <mi>b</mi> </msub> <mrow> <mn>2</mn> <msqrt> <mn>2</mn> <mi>σ</mi> </msqrt> </mrow> </mfrac> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mi>erfc</mi> <mo>[</mo> <mfrac> <msqrt> <mn>2</mn> </msqrt> <mn>2</mn> </mfrac> <msup> <mrow> <mo>(</mo> <mfrac> <msub> <mi>N</mi> <mn>1</mn> </msub> <msub> <mi>E</mi> <mi>b</mi> </msub> </mfrac> <mo>+</mo> <mfrac> <msub> <mi>N</mi> <mn>2</mn> </msub> <msub> <mi>E</mi> <mi>b</mi> </msub> </mfrac> <mo>+</mo> <mfrac> <msub> <mi>N</mi> <mn>1</mn> </msub> <msub> <mi>E</mi> <mi>b</mi> </msub> </mfrac> <mfrac> <msub> <mi>N</mi> <mn>2</mn> </msub> <msub> <mi>E</mi> <mi>b</mi> </msub> </mfrac> <mi>M</mi> <mo>)</mo> </mrow> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </msup> <mo>]</mo> </mtd> </mtr> </mtable> <mrow> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>22</mn> <mo>)</mo> </mrow> </mrow> </mfenced> </math>

The initial values used for generating the chaotic signals in each bit period are different, chaotic signal sample values generated by the same initial value have strong correlation, and chaotic signal sample values generated by different initial values are irrelevant. The non-coherent demodulation of the chaotic signal can be realized by utilizing the correlation and the non-correlation at the receiving end.

Logistic sequence of when mu₁=2.9，μ ₂2=3.0 can generate chaotic signals. Let the initial value x_i,1=0.1, and the chaotic signal generated by 50 iterations is used as a carrier to modulate the original signal, as shown in (23) (24).

Simulation result and performance analysis: the transmission process in a wireless channel is simulated, assuming that the channel noise satisfies the AWGN distribution.

FIG. 6 shows a conventional DAnd comparing the bit error rate between the CSK and the modified DCSK, wherein the solid line represents the conventional DCSK, and the dotted line represents the modified DCSK. It can be seen that the improved DCSK has been greatly improved over the conventional DCSK. Comparing the error code performance of the DCSK system before and after the improvement under the same spreading factor M, it can be known that the error code rate difference of the two systems is not large when the signal to noise ratio is low, and when E is_b/N₀And when the bit error rate is more than 7.5dB, the difference of the bit error rates begins to increase, and the bit error rate of the improved DCSK is lower than that of the traditional DCSK. At the same E_b/N₀The bit error rate of the improved DCSK is 1-2 orders of magnitude lower than that of the traditional DCSK; the signal-to-noise ratio also varies for the same BER, and when BER =10-3 and M =10, the improved DCSK is approximately 6dB higher than the conventional DCSK.

The error performance of the DCSK system has a great relationship with M. Fig. 7 shows the error performance simulation of the improved DCSK system when M is 10, 20, 30, 40 and 50 respectively. When M increases, the system BER also increases, and the error performance is also worse.

Fig. 8 shows the relationship between M and BER for different signal-to-noise ratios. It can be seen from the figure that the larger the signal-to-noise ratio at the same M, the lower the BER.

In general, the performance of the improved DCSK system is obviously better than that of the traditional system, and the error code performance and the confidentiality of data transmission are greatly improved.

The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall within the scope of the invention defined by the method claims.

Claims

1. An improved differential chaos keying DCSK secret communication method is characterized by comprising the following steps:

101. generating two different chaotic signals by adopting Logistic chaotic mapping generator at transmitting end of chaotic system

And chaotic signal

And will chaos signal

And chaotic signal

And delaying the chaotic signal

102. Message to be sent

Andand will bipolar signal

And the delayed chaotic signal obtained in the step 101

Multiplying to obtain a transmission signal

Put in channel I for transmission, the bipolar signal

And the one obtained in step 101Delaying chaotic signals

Multiplying to obtain a transmission signalPlaced in channel II for transmission, the output signal of channel I being

The output signal of the channel II is

In which the channel I is in the first half of a symbol period T

The channel transmits the reference signal, and the second half

The periodic channel transmitting a transmission signal

First half period of channel II

The channel transmits the reference signal, and the second half

The periodic channel transmitting signals

103. When the output signal of channel I in step 102

Output signal of channel II

2. The improved DCSK (differential chaos keying) secret communication method as claimed in claim 1, wherein the Logistic chaos mapping generator in step 101 has the expression of

Where x (n) is the chaotic signal, μ is the coefficient, when μ =2.9 and

generating chaotic signal by Logistic chaotic mapping generator when mu =3.0And chaotic signal

3. The improved DCSK secure communication method according to claim 1, wherein the expression of autocorrelation in step 104 is

Wherein r (n) represents the received signal, and r (n) includes r_1,nAnd r_2,nAnd r (n + M) represents a signal delayed by M bits, M being a spreading factor.