CN105915480A - Efficient chaotic communication scheme based on orthogonal chaotic generator - Google Patents

Abstract

The invention provides an efficient chaotic differential communication scheme based on an orthogonal chaotic generator, and belongs to the field of communication systems. A DCSK (Differential Chaos Shift Keying) signal frame is extended in order that each frame includes N equal-length time slots, and a system modulates chaotic carrier waves in the time slots, namely, each time slot carries 1 bit of user data. Each time slot takes a signal in a previous time slot as a reference signal. A reference signal of a first time slot is in a last time slot of a previous frame, namely, a last time slot of each frame carries user information of the time slot and a signal which can be converted into a reference signal of a next frame. Meanwhile, the orthogonal chaotic generator is designed to generate strictly-orthogonal chaotic signals in order that the chaotic carrier wave of each frame and a carrier wave of an adjacent frame are kept orthogonal, and the system is free from inner-signal interference. An incoherent demodulation way is adopted at a demodulation end; correlation operation is performed on signals in front and back adjacent frames through a correlator; and user data can be judged through a judgement threshold. According to the scheme, the transmission rate is two times that of DCSK, and bit error rate performance is superior to that of DCSK in any signal-to-noise ratio range.

Description

Efficient chaos communications based on orthogonal chaos signal generator

Technical field

It is contemplated that design a kind of Efficient Difference chaos communications (OHE-based on orthogonal chaos signal generator DCSK), specially difference chaotic offset keying (DCSK) technology is improved so that its transfer rate doubles and greatly improves Its bit error rate performance.

Background technology

It is the incoherent chaos digital modulation scheme of a kind of main flow as technology DCSK in IEEE802.11WLAN standard. Recently, DCSK technology starts to be applied to IEEE 802.15.4a low speed ultra broadband standard.DCSK technology uses transmission reference (transmitted-reference, T-R) mode, is all sent to recipient by the signal of reference carrier with the information of carrying, it is not necessary to Complete channel necessary to conventional spread spectrum communication system to estimate and spread and disposal plus, enormously simplify system structure and have the strongest Anti-fading characteristic.But, the bit-time transmission of DCSK system cost half reference the chaos load without any data message Ripple, the Bit Transmission Rate of system is relatively low.On the other hand, owing to using T-R technology, the reference signal in same bit-time There is certain similarity (identical or contrary) with information signal, square composing it is known that bit passes by observation signal Defeated speed.Therefore, there is certain defect in DCSK in terms of Information Security.

In sum, very important one during DCSK technology would is that personal radio communication even moving communicating field Communication plan, therefore more and more important to DCSK research.The research of DCSK technology mainly includes improving transfer rate, improving letter Number square spectrum of defect.These researchs have important for chaotic signal application, secret communication, WPC and cellular communication Effect.

Research Literature currently for DCSK technology is the most, but major part research is all to sacrifice a kind of performance indications as generation Valency improves another kind of performance indications.Document " Lau F C M.Permutation-based DCSK and multiple Access DCSK systems.IEEE Transactions on Circuits and Systems I, 2003 " propose based on The P-DCSK technology of permutation matrix, utilizes permutation matrix to upset the sequencing of chaotic signal sampling, destroys reference signal and letter Similarity between information signal, has stopped to find out the probability of bit rate from square spectrum, has enhanced Information Security.But P-DCSK does not improve for DCSK error performance and transfer rate.Document " Yang Hua .Reference-Modulated DCSK:A Novel Chaotic Communication Scheme.IEEE Transactions on Circuits and Systems II, 2013 " RM-DCSK is proposed, this technology is modulated by reference signal so that pass in each time slot Defeated 1bit data, transfer rate improves 1 times.By adding the reference signal of next time slot in each time slot, RM-DCSK uses The receiver identical with DCSK just can realize demodulation.But RM-DCSK is owing to making signal the most in the same time be placed in same time slot, Receiving terminal judgment variables does not only has interchannel noise interfere, the cross-correlation components of chaotic signal the most in the same time, i.e. Signal internal interference, is degrading error performance.

Summary of the invention

The technical problem to be solved, for existing improvement DCSK technology exist transfer rate is low or error code The defects such as energy difference, propose a kind of modified model scheme to DCSK.The program is under small sacrifice DCSK complexity premise, and transmission is fast Rate is the twice of DCSK, and the bit error rate is superior to DCSK under the conditions of any signal to noise ratio.

The present invention solves the technical scheme of above-mentioned technical problem: expand DCSK signal frame, makes each frame comprise N Individual isometric time slot, the chaotic carrier in each time slot is modulated by system, and the most each time slot all carries 1bit user data.Often One time slot all using the signal in previous time slot as reference signal.Last in former frame of the reference signal of first time slot In one time slot, last time slot of i.e. every frame not only carries the user profile of this time slot and also carries and can be converted into next frame ginseng Examine the signal of signal.Meanwhile, devise a kind of orthogonal chaos signal generator, produce the chaotic signal of strict orthogonal, make each The chaotic carrier of frame and the carrier wave of consecutive frame keep orthogonal, it is ensured that without signal internal interference in system.Demodulating end uses incoherent Demodulation mode, utilize correlator that signal in front and back's consecutive frame is carried out related operation, be then passed through decision threshold；Can adjudicate Go out user data.This demodulation mode, it is not necessary at demodulating end with walking out of chaotic carrier, it is not required that conventional spread spectrum communication is musted The channel needed is estimated, therefore structure is the simplest.

Utilize Gaussian approximation (GA), derive OHE-DCSK scheme of the present invention theoretical bit error rate in awgn channel public Formula, and contrasted by theoretical formula and Monte Carlo simulation, it was demonstrated that the correctness of theoretical derivation.Simultaneously with existing several Classical class DCSK scheme contrasts, it was demonstrated that the high efficiency of OHE-DCSK scheme.

Accompanying drawing explanation

Fig. 1 OHE-DCSK of the present invention scheme signal frame assumption diagram；

Fig. 2 OHE-DCSK of the present invention scheme orthogonal chaos signal generator structure chart；

Fig. 3 OHE-DCSK of the present invention scheme transmitting terminal structure chart；

Fig. 4 OHE-DCSK of the present invention scheme receiving terminal structure chart；

Fig. 5 OHE-DCSK of the present invention option b ER is with spreading factor change curve；

Fig. 6 OHE-DCSK of the present invention option b ER is with signal to noise ratio change curve；

Fig. 7 OHE-DCSK of the present invention option b ER is with timeslot number change curve；

Fig. 8 OHE-DCSK of the present invention scheme and several classical system BER comparison diagram；

Detailed description of the invention

Below in conjunction with accompanying drawing and instantiation, the enforcement to the present invention is further described.

Fig. 1 provides the frame structure of OHE-DCSK system kth frame signal.Every frame comprises N number of a length of T_sIsometric time slot；Often The chaos sequence of a length of β of slot transmission, i.e. spreading factor are β；b_jRepresent the data bit of kth frame jth time slot modulation.Following Analyze all as a example by kth frame.The 1st slot transmission of kth frame is S₁=b₁X_k, wherein X_k=[x_k(1),x_k(2),...,x_k (β)] it is the chaos sequence of a length of β.2nd slot transmission is S₂=b₂S₁=b₂b₁X_k, it is with the signal S in the 1st time slot₁ For reference signal.Nth slot not only transmits current demand signal b_NS_N-1, also comprise and can be converted into next frame reference signalI.e.

Fig. 2 designs a kind of orthogonal chaos signal generator (Orthogonal Chaotic generator, OCG), permissible Produce the chaotic signal of strict orthogonal.In fig. 2, the arrow entering multiplier represents two components participating in multiplying.WithFor second order Walsh code.Work process concrete for OCG is as follows: chaos signal generator is first First produce the chaos sequence U of a length of β/2.In upper branch road, useEach element being multiplied by sequence, available a length of β's Chaos sequence；In like manner, in lower branch road, useIt is multiplied by each element in same section of sequence after delay, another section available The chaos sequence of a length of β.These two sections of i.e. strict orthogonal of sequence.

Fig. 3 provides OHE-DCSK transmitting terminal structure.Compared with DCSK transmitting terminal, OHE-DCSK transmitting terminal is the most complicated.This It is owing to new system has expanded the frame structure of DCSK, adds delay cell and multiplier.

When system is operated in kth frame 1 time slot, branch road under the switch connection of OCG in Fig. 2, in Fig. 3, transmitting terminal switch connects Logical #1 branch road；2nd to N-1 time slot, and the switch of OCG is in vacant state, and transmitting terminal switch in turn switches on #1 to #N-1 and props up Road；During nth slot, branch road on the switch connection of OCG, transmitting terminal switch connection #N branch road；1st time slot of kth+1 frame, OCG opens Closing and connect again lower branch road, transmitting terminal switch is connected again #1 branch road, is completed a working cycle.

How explanation OCG ensures that chaotic signal is mutually orthogonal and coordinates transmitting terminal work more detail below.If it is each Length β=6 of chaos sequence in time slot.Chaos signal generator produces the chaos of a length of β/2=3 in kth-1 frame the 1st time slot Sequence U=[a, b, c].In kth frame the 1st time slot, branch road under OCG switch connection, Enter transmitting terminal, transmitting terminal switch connection #1 branch road, user profile b₁Modulation X_k, S₁=b₁X_kLaunch.2nd to N-1 Time slot, the switch of OCG is in vacant state, does not has new chaos sequence to enter transmitting terminal, and transmitting terminal switch in turn switches on #1 to #N- 1 branch road, user profile b_iModulation S_i-1, S_i=b_iS_i-1(i=2 ..., N-1) launch.During nth slot, chaotic signal occurs The chaos sequence V=[x, y, z] of device one section of new a length of β/2=3 of generation, branch road on the switch connection of OCG,Entrance transmitting terminal, transmitting terminal switch connection #N branch road,Send out It is shot out.1st time slot of kth+1 frame, OCG switch connects again lower branch road, V after postponing withIt is multiplied, is formedEnter transmitting terminal, complete a working cycle.It should be noted that: kth+1 It is X that frame really carries the carrier wave of information_k+1, and the reference signal that kth frame nth slot is carried isTherefore, demodulating information ratio Must be by time specialBe converted to X_k+1Could demodulate smoothly.

By observing X_k=[a ,-a, b ,-b, c ,-c],And X_k+1=[x ,-x, y ,-y, z ,- Z] form, the chaos sequence that can obtain OCG output meets following relation:

$\left\{\begin{array}{c}{X}_k\⊥{\tilde{X}}_{k+1}\\ {\tilde{X}}_{k+1}\⊥X_{k+1}\\ X_{k+1}=\left({\tilde{X}}_{k+1}W\right)\\ X_{k+1}\⊥\left(X_{k}W\right)\end{array}\right.---\left(1\right)$

Wherein W=[1 ,-1 ... 1 ,-1], its length is equal to spreading factor β.

In sum, OHE-DCSK system kth frame signal expression is:

$\left\{\begin{array}{c}{S}_1=b_1{X}_k\\ S_l=b_l{S}_{l-1},(l=2,...,N-1)\\ s_N=b_N{S}_{N-1}+{\tilde{X}}_{k+1}\end{array}\right.---\left(2\right)$

Fig. 4 provides OHE-DCSK receiving terminal structure.In the diagram, r_lRepresent that the transmitting signal in kth frame l time slot passes through The reception signal of receiving terminal is arrived after awgn channel.OHE-DCSK receiving terminal is similar to that DCSK receiving terminal structure, all makes Use non-coherent demodulation.The difference of structure is: relative to DCSK, adds be multiplied by W to realize accurately demodulating OHE-DCSK Module.Its specific works process is as follows: demodulation b₁Time, branch road on the switch connection in Fig. 4, during by W by kth-1 frame N Carry in gapIt is converted into reference signal X that kth frame is actual_k, i.e.Then system is by r₁And r₀Carry out phase Close computing (being completed by multiplier and adder), finally result is made decisions, recover data bit.Demodulation kth frame remaining In time slot during data bit, branch road under the switch connection in Fig. 4, then identical with DCSK demodulation mode, directly postpone Related operation.

The signal of the kth frame l time slot that OHE-DCSK receiving terminal receives is:

r_l=s_l+ξ_l (3)

Make ξ_lRepresenting the additive white Gaussian noise in awgn channel, its average is zero, and variance is N₀/2。

Receiving terminal correlator is output as:

$\left\{\begin{array}{c}{c}_1=r_1\·rw_{\stackrel{\·}{0}}\\ c_l=r_l\·r_{l-1},(l=2,...,N)\end{array}\right.---\left(4\right)$

According to (5) formula, correlated results is made decisions, i.e. can get information bit:

${\hat{b}}_l=\left\{\begin{array}{c}+1,c_l>0\\ -1,c_l<0\end{array}\right.---\left(5\right)$

Utilize the GA derivation OHE-DCSK system bit error rate in awgn channel.The average bit of system can be obtained according to Fig. 1 Energy (sending the energy required for a bit) E_b:

$E_b=\frac{N+1}{N}E\left(X_k^2\right)=\frac{N+1}{N}\mathrm{\&beta;}E\&lsqb;x_k^2\left(i\right)\&rsqb;---\left(6\right)$

Wherein, E () is expectation operator.

With b₂And b_NAs a example by analyze the bit error rate of whole system.Wushu (2) and formula (3) are brought (4) into and can be obtained:

$\begin{array}{c}{c}_2=r_2\&CenterDot;r_1=(S_2+{\mathrm{\&xi;}}_2)\&CenterDot;(S_1+{\mathrm{\&xi;}}_1)\\ =(b_2{b}_1{X}_k+{\mathrm{\&xi;}}_2)\&CenterDot;(b_1{X}_k+{\mathrm{\&xi;}}_1)\\ =A+B+{\mathrm{\&xi;}}_1\&CenterDot;{\mathrm{\&xi;}}_2\\ C\end{array}---\left(7\right)$

Wherein,

A=b₂(b₁X_k)²=b₂(X_k)² (8)

B=b₂b₁X_kξ₁+b₁X_kξ₂ (9)

In above-mentioned analysis, A is useful signal component, B and C is the interference components that interchannel noise causes.According to center pole Limit reason, when spreading factor β is bigger, the equal Gaussian distributed of formula (7) each component, as long as i.e. expectation and variance just can be retouched completely State its statistical property.Assume b₂=1, then judgment variables c₂Average can be expressed as E (c₂)=E (A)+E (B)+E (C), wherein

$E\left(A\right)=E\left(X_k^2\right)=\frac{{\mathrm{NE}}_b}{N+1}---\left(10\right)$

E (B)=E (C)=0 (11)

Judgment variables c₂Variance can be expressed as Var (c₂)=Var (A)+Var (B)+Var (C), wherein

$Var\left(A\right)=Var\&lsqb;b_2{\left(X_k\right)}^2\&rsqb;=\mathrm{\&beta;}Var\left(x_i^2\right)---\left(12\right)$

$Var\left(B\right)=Var\left(X_k\right)\frac{N_0}{2}+Var\left(X_k\right)\frac{N_0}{2}=\frac{{\mathrm{NE}}_b{N}_0}{N+1}---\left(13\right)$

$Var\left(C\right)=Var({\mathrm{\&xi;}}_1\&CenterDot;{\mathrm{\&xi;}}_2)=\mathrm{\&beta;}\frac{N_0^2}{4}---\left(14\right)$

Wherein, Var () is variance operator.Therefore, it can obtain c₂Average and variance be:

$E\left(c_2\right)=\frac{{\mathrm{NE}}_b}{N+1}---\left(15\right)$

$Var\left(c_2\right)=\mathrm{\&beta;}Var\left(x_i^2\right)+\frac{{\mathrm{NE}}_b{N}_0}{N+1}+\frac{{\mathrm{\&beta;N}}_0^2}{4}---\left(16\right)$

Assume that chaos signal generator uses Logistic to map,-1 ＜ x_i＜ 1, x_i≠±0.5WithSystem equiprobability sends data bit (+1 ,-1), can obtain OHE-DCSK demodulates b₂BER formula:

$\begin{array}{c}{\mathrm{BER}}_{b_2}=\frac{1}{2}erfc\&lsqb;\frac{E\left(c_2\right|b_2=+1)}{\sqrt{2Var\left(c_2\right|b_2=+1)}}\&rsqb;=\\ \frac{1}{2}erfc\left\{{\&lsqb;\frac{1}{\mathrm{\&beta;}}+\frac{2(N+1)}{N}{\left(\frac{E_b}{N_0}\right)}^{-1}+\frac{{(N+1)}^2\mathrm{\&beta;}}{2N^2}{\left(\frac{E_b}{N_0}\right)}^{-2}\&rsqb;}^{-\frac{1}{2}}\right\}\end{array}---\left(17\right)$

The most in a similar manner, demodulation b is calculated_NBER formula.

Wherein,

A=b_N(b_N-1…b₁X_k)²=b_N(X_k)² (19)

$B=(b_N...b_1)X_k{\mathrm{\&xi;}}_{N-1}+(b_{N-1}...b_1)X_k{\mathrm{\&zeta;}}_N+{\tilde{X}}_{k+1}{\mathrm{\&xi;}}_{N-1}---\left(20\right)$

D component in formula (18) is signal internal interference component.The relation be given according to formula (1), it is known that D=0, i.e. OHE- DCSK judgment variables does not contains signal internal interference component.Assume b_N=1, then judgment variables c_NAverage and variance can be expressed as:

$E\left(c_N\right)=E\left(X_k^2\right)=\frac{{\mathrm{NE}}_b}{N+1}---\left(21\right)$

$Var\left(c_N\right)=\mathrm{\&beta;}Var\left(L^2\right)+\frac{3}{2}\frac{{\mathrm{NE}}_b{N}_0}{N+1}+\frac{{\mathrm{\&beta;N}}_0^2}{4}---\left(22\right)$

Thus can obtain OHE-DCSK and demodulate b_NBER formula:

${\mathrm{BER}}_{b_N}=\frac{1}{2}erfc{\&lsqb;\frac{1}{\mathrm{\&beta;}}+\frac{3(N+1)}{N}{\left(\frac{E_b}{N_0}\right)}^{-1}+\frac{{(N+1)}^2\mathrm{\&beta;}}{2N^2}{\left(\frac{E_b}{N_0}\right)}^{-2}\&rsqb;}^{-\frac{1}{2}}---\left(23\right)$

To sum up can obtain the BER formula of OHE-DCSK:

$\begin{array}{c}{\mathrm{BER}}_{OHE-DCSK}=\frac{2}{N}\&CenterDot;{\mathrm{BER}}_{b_N}+\frac{N-2}{N}\&CenterDot;{\mathrm{BER}}_{b_2}\\ =\frac{1}{N}erfc\left\{{\&lsqb;\frac{1}{\mathrm{\&beta;}}+\frac{3\left(N+1\right)}{N}{\left(\frac{E_b}{N_0}\right)}^{-1}+\frac{{(N+1)}^2\mathrm{\&beta;}}{2N^2}{\left(\frac{E_b}{N_0}\right)}^{-2}\&rsqb;}^{-\frac{1}{2}}\right\}+\\ \frac{N-2}{2N}erfc\left\{{\&lsqb;\frac{1}{\mathrm{\&beta;}}+\frac{3\left(N+1\right)}{N}{\left(\frac{E_b}{N_0}\right)}^{-1}+\frac{{(N+1)}^2\mathrm{\&beta;}}{2N^2}{\left(\frac{E_b}{N_0}\right)}^{-2}\&rsqb;}^{-\frac{1}{2}}\right\}\end{array}---\left(24\right)$

Fig. 5, Fig. 6, Fig. 7 and Fig. 8 represent OHE-DCSK option b ER respectively with spreading factor, signal to noise ratio, the change of timeslot number Curve chart and and several classical system BER comparison diagrams.As can be seen from the figure: when spreading factor β is bigger theoretical value and It is the best that Monte Carlo emulation coincide, it was demonstrated that the correctness of theory analysis；On the other hand, suitable β is chosen to being System performance has a significant impact, and under different signal to noise ratios, BER exists extreme value.I.e. for specific signal to noise ratio, there is an optimal β value (β_opt) make BER minimum；At specific E_b/N₀With under β, BER increases along with N and diminishes, and finally tends to constant, i.e. the theory of system There is theory lower-bound in BER, BER can be made to level off to this lower bound by increasing by the way of N；At BER=10^-5Time, OHE-DCSK Relatively RM-DCSK and DCSK is better than 2dB and 4dB respectively.

The present invention, by DCSK frame structure is expanded and improved, makes transfer rate double.And utilize second order Walsh code orthogonality, devises a kind of orthogonal chaos signal generator, produces the chaotic signal of strict orthogonal, it is possible to avoid be System occurs signal internal interference.Tested by substantial amounts of Monte-Carlo Simulation, it was demonstrated that the correctness of theory analysis.Research in detail Systematic function and the isoparametric relation of spreading factor, timeslot number and signal to noise ratio.Simultaneously with two kinds of classical systems DCSK and RM- DCSK compares, and demonstrates OHE-DCSK high efficiency in terms of error performance.This programme all has under any signal to noise ratio Good error performance, significant.

Claims (3)

1. a chaos efficient communication scheme based on orthogonal chaos signal generator, its step is, by DCSK signal Frame is expanded, and makes each frame comprise N number of isometric time slot, and the chaotic carrier in each time slot is modulated by system, the most each Time slot all carries 1bit user data.Each time slot using the signal in previous time slot as reference signal.When first The reference signal of gap is in last time slot of former frame, and last time slot of i.e. every frame not only carries the user of this time slot Information also carries the signal that can be converted into next frame reference signal.Meanwhile, devise a kind of orthogonal chaos signal generator, produce The chaotic signal of strict orthogonal, makes the chaotic carrier of each frame and the carrier wave of consecutive frame keep orthogonal, it is ensured that without letter in system Number internal interference.Demodulating end uses noncoherent demodulation mode, utilizes correlator that signal in front and back's consecutive frame is carried out related operation, It is then passed through decision threshold；User data can be ruled out.

Communication plan the most according to claim 1, it is characterised in that each time slot of the program all transmits 1bit user's letter Breath, each frame all treats as reference signal the signal of its former frame, and the chaotic carrier of consecutive frame ensures strict orthogonal, thoroughly disappears Except signal internal interference.

Method of estimation the most according to claim 1, it is characterised in that receiving terminal demodulation method and the tradition asynchronous solution of chaos Adjusting consistent, the method uses simple delay relevant, and method is simple, it is achieved easily cutting circuit simple, hardware cost is low.