CN105429747A - Frequency-domain chaotic cognitive radio system based on subcarrier dislocation - Google Patents

Abstract

The invention discloses a frequency-domain chaotic cognitive radio system based on subcarrier dislocation. The system comprises a sending end and a receiving end; at the sending end, a frequency-domain chaotic signal generator generates a frequency domain based chaotic signal c(t), a subcarrier corresponding module dynamically changes the correspondence between a chaotic sequence C(k) and subcarriers, BPSK modulation is carried out on data information to obtain b(t), the b(t) is modulated by c(t) into s(t), and s(t) is sent to a wireless channel of an available frequency band after carrier modulation; and at the receiving end, after carrier coherent demodulation, a frequency-domain chaotic signal generator generates a frequency domain based chaotic signal c(t), the chaotic signals demodulates a receiving signal r(t) to obtain d(t) after synchronization, zero-crossing decision is carried out on the d(t) to obtain the estimated value of the information bit, and the sent information is received successfully. Compared with an original frequency-domain chaotic cognitive radio system, the safety level of the system in the invention is improved obviously.

Description

A kind of frequency domain chaos cognitive radio system based on subcarrier displacement

Technical field

The present invention, towards wireless communication field, proposes a kind of frequency domain chaos cognitive radio system based on subcarrier displacement, carrys out transmission information by the chaos sequence-subcarrier pair of stochastic generation, improve the security feature of cognitive radio system.

Background technology

Frequency spectrum is congested is the bottleneck affecting performance in wireless communication systems, and cognitive radio technology can detect available frequency band, thus carries out accessing in discrete frequency cavity thus make Signal transmissions obtain more bandwidth.

But cognitive radio communication systems is the same with other wireless communication system, because wireless channel is broadcast channel, information is easy to be ravesdropping user or malicious attacker interception, and the safe transmission of information is on the hazard and can not be protected.

In order to improve the fail safe of cognitive radio system, existing document proposes chaos treatment technology to be applied to cognitive radio system, thus forms tool high security and the high spectrum utilization of dynamic spectrum access technology and the frequency domain chaos cognitive radio system of utilization rate.

Frequency domain chaos cognitive radio system structure as shown in Figure 1, at transmitting terminal, generates chaotic signal c (t) based on frequency domain by frequency domain chaotic signal generator.Data message obtains b (t) through BPSK (BinaryPhaseShiftKeying) modulation, and b (t), by c (t) modulation, is then sent to the wireless channel of available band by carrier modulation.At receiving terminal, after carrier coherent demodulating, chaotic signal c (t) is generated with the process identical with transmitting terminal, chaotic signal after synchronization to received signal r (t) carry out demodulation and obtain d (t), then zero passage judgement is carried out to d (t) and obtain b (i), successfully receive sent information.

Frequency domain multi-subcarrier chaotic signal generator concrete structure as shown in Figure 2, in conjunction with the spectrogram that cognitive radio system detecting surrounding radio environment obtains, chaos sequence C (k) have passed through multiple available orthogonal OFDM (OrthogonalFrequencyDivisionMultiplexing) subcarrier-modulated.At interpolation Cyclic Prefix, serial/parallel conversion and will chaotic signal c (t) be produced after low pass filter.

Following single order LogisticMap chaos sequence generator can be adopted to produce chaos sequence, and then produce chaotic signal c (t):

C(k)＝4C(k-1)-4C ²(k-1)k＝1,2,…，C(k)∈(0,1)(1)

Although above-mentioned frequency domain chaos process cognitive radio system improves the security performance of system, but be easy to know chaos sequence generator and the initial value calculating chaos sequence due to information intercepting person, thus regeneration obtains chaos sequence, therefore, existing frequency domain chaos process cognitive radio system is still difficult to the application demand meeting high security.

Summary of the invention

The present invention is for overcoming at least one defect (deficiency) described in above-mentioned prior art, the present invention is intended to the fail safe that physical layer improves communication system, zygote carrier wave interleaving technology and chaos sequence Dynamic iterations, a kind of frequency domain chaos cognitive radio system based on subcarrier displacement is proposed, thus effectively resist assailant by rebuilding the attack carried out of chaos, improve the fail safe of frequency domain chaos cognitive radio system.

For solving the problems of the technologies described above, technical scheme of the present invention is as follows:

A kind of frequency domain chaos cognitive radio system based on subcarrier displacement, comprise transmitting terminal and receiving terminal, at transmitting terminal, first generate chaos sequence C (k) by chaos sequence generator, then realize chaos sequence C (k) by subcarrier respective modules dynamically to change with subcarrier corresponding relation, chaotic signal c (t) based on frequency domain is generated again by frequency domain chaos signal generator, input data information obtains b (t) through BPSK modulation, b (t) is modulated into s (t) by c (t), is then sent to the wireless channel of available band by carrier modulation; At receiving terminal, after carrier coherent demodulating, chaotic signal c (t) based on frequency domain is generated equally by frequency domain chaos signal generator, chaotic signal c (t) after synchronization to received signal r (t) carry out demodulation and obtain d (t), then the estimated value that zero passage judgement obtains information bit is carried out to d (t) successfully receive sent information.

Preferably, described subcarrier respective modules realizes the concrete mode that chaos sequence C (k) dynamically changes with subcarrier corresponding relation and is:

Subcarrier shift unit dynamically to match with subcarrier to chaos sequence C (k) and modulates, and this pair relationhip is determined jointly by subcarrier shift unit and frequency band mapping graph;

Wherein, frequency spectrum mapping graph is that the frequency spectrum service condition that cognitive radio system perception surrounding spectrum situation obtains obtains:

Be map the C (k) of input, when the individual sub-carrier occupancy of kth, its frequency a (k) sets to 0, and when a kth subcarrier is idle, its frequency a (k) is then set to 1,

Make the signal after IFFT only comprise idle frequency component, after obtaining frequency spectrum service condition information, according to frequency band mapping graph to idle sub-carrier with cycle T _sScarry out dynamic shift, after displacement, obtain the chaos sequence of one section of particular arrangement, use sequence C (k) and formula (3)-(6), generate and based on after chaotic signal c (t) of frequency domain, communication information b (t) is modulated, make listener-in be difficult to crack communication system thus obtaining communication information, dynamic shift Rule Expression is a shift matrix a N _nC× N _nCmatrix, wherein, N _nCfor the used number of sub carrier wave that cognitive radio system detects, k=1,2 ..., N _nC; Shift matrix be N by a dimension _nCthe chaos sequence C of × 1 _mk () determines, C (k) is above for OFDM modulation, finally generates the input chaos sequence of c (t), and C _mk () is for generating shift matrix chaos sequence, they all by formula (1) produce, just by different initial value C (1), carry out iteration.Along with C _mthe Dynamic iterations of (k), matrix dynamically changes thereupon;

Described that every a line and each row all only have a nonzero element " 1 ", by chaos sequence C _mk the sequence from small to large of (), obtains the chaos sequence C sorted _mSortk (), by C _m(k) and C _mSortk () generates and be one can by C _mk () is transformed to C _mSortthe matrix of (k), conversion expression formula is:

$C_{MSort}\left(k\right)=M_{N_{NC}}{C}_M\left(k\right)---\left(3\right)$

Can be obtained by (3):

$M_{N_{NC}}=f_S\left(C_{MSort}\right(k){\[C_M\left(k\right)\]}^{-1})---\left(4\right)$

In (4), ${\[C_M\left(k\right)\]}^{-1}=(\frac{1}{C_M\left(1\right)},\frac{1}{C_M\left(2\right)},...,\frac{1}{C_M\left(N_{NC}\right)}),$ Function f _s() is defined as:

Above-mentioned B _i,jthe element of the i-th row jth row of matrix B, AA represents a random matrix, herein for illustration of f _sthe definition of (), A _i,jthe element of the i-th row jth row of representing matrix A;

Due to chaos sequence C _mk () by chaos sequence generator Dynamic iterations, just can change once at regular intervals, also dynamic change thereupon, makes assailant be difficult to obtain subcarrier displacement rule, significantly enhances the fail safe of transmission data;

After dynamic shift process, OFDM subcarrier-modulated is carried out to chaos sequence; At interpolation Cyclic Prefix, serial/parallel conversion and will chaotic signal c (t) be produced after low pass filter;

$c\left(t\right)=\underset{k=1}{\overset{N}{\Σ}}C\left(k\right)a\left(k\right)e^{j2\mathrm{\π}k\mathrm{\Δ}ft}p\left(t\right)---\left(6\right)$

Wherein N represents total chaos sequence length, and C (k) represents the chaos sequence that kth item is produced by chaos sequence generator; K Δ f represents a kth subcarrier, wherein t _sfor the symbol period of OFDM; The unit height square wave of p (t) to be width a be symbol period.

Preferably, in the middle of the frequency domain chaos cognitive radio system be shifted based on subcarrier, the binary bits b (t) of BPSK to input system is used to modulate, and be multiplied with chaotic signal c (t) of OFDM modulation and obtain s (t), s (t) is expressed as:

$s\left(t\right)=b\left(t\right)c\left(t\right)=\left\{\begin{array}{cc}+c\left(t\right),if& b\left(t\right)=+1\\ -c\left(t\right),if& b\left(t\right)=-1\end{array}\right.---\left(9\right)$

Through carrier wave cos (2 π f _ct), after modulation, signal is sent to awgn channel;

At receiving terminal, receive the signal expression of t:

r(t)＝s(t)+n(t)(10)

Wherein, n (t) is average is 0, and variance is noise signal, generates c (t), r (t) and c at receiving terminal with flow process identical with transmitting terminal ^*t () obtains d (t) after carrying out demodulation:

d(t)＝r(t)c ^*(t)＝b(t)|c(t)| ^*+n(t)c ^*(t)(11)

Then the estimated value that zero passage judgement obtains information bit is carried out to d (t) complete communication process.

Compared with prior art, the beneficial effect of technical solution of the present invention is: the present invention is zygote carrier wave interleaving technology and chaos sequence Dynamic iterations production process, a kind of frequency domain chaos cognitive radio system based on subcarrier displacement of proposition.Within the system, user carrys out transmission information by chaos subcarrier pair, and wherein, chaos subcarrier pair is that the idle available subcarrier detected by chaos sequence and cognitive radio system combines and obtains.The corresponding relation of chaos sequence and available subcarrier carries out dynamic shift according to shift cycle, shift rule is that the chaos sequence generated by another different chaos sequence generator defined, like this, along with the Dynamic iterations of chaos sequence produces, shift rule dynamic change, effectively prevent assailant and obtains shift rule.From theory analysis and simulation result, the fail safe of frequency domain chaos cognitive radio system to original frequency domain chaos cognitive radio system based on subcarrier displacement proposed by the invention has clear improvement.

Accompanying drawing explanation

Fig. 1 is frequency domain chaos cognitive radio system structural representation.

Fig. 2 is frequency domain multi-subcarrier chaotic signal generator structural representation.

Fig. 3 is the frequency domain chaos cognitive radio system schematic diagram based on subcarrier displacement.

Fig. 4 is frequency domain chaotic signal generator modular structure schematic diagram corresponding to subcarrier.

Fig. 5 is the exemplary plot of subcarrier shift unit.

Fig. 6 is System performance profiles figure.

Embodiment

Accompanying drawing, only for exemplary illustration, can not be interpreted as the restriction to this patent; In order to better the present embodiment is described, some parts of accompanying drawing have omission, zoom in or out, and do not represent the size of actual product;

To those skilled in the art, in accompanying drawing, some known features and explanation thereof may be omitted is understandable.Below in conjunction with drawings and Examples, technical scheme of the present invention is described further.

The present invention is the fail safe utilizing subcarrier shifting technique to improve frequency domain chaos cognitive radio system.Zygote carrier wave shifting technique and frequency domain chaos cognitive radio system, can obtain based on subcarrier displacement frequency domain chaos cognitive radio system structure as shown in Figure 3.Compared with the frequency domain chaos cognitive radio system in Fig. 1, difference part is, in the system of figure 3, propose subcarrier dynamic shift module, namely " subcarrier respective modules " in figure, realizes the dynamic change that subcarrier-chaos sequence is right, improves the fail safe of information transmission.

System configuration

As Fig. 3, at transmitting terminal, generate chaotic signal c (t) based on frequency domain by frequency domain chaotic signal generator, subcarrier respective modules achieves chaos sequence C (k) and dynamically changes with subcarrier corresponding relation.Data message obtains b (t) through BPSK modulation, and b (t), by c (t) modulation, is then sent to the wireless channel of available band by carrier modulation.At receiving terminal, after carrier coherent demodulating, chaotic signal c (t) is generated with the process identical with transmitting terminal, chaotic signal after synchronization to received signal r (t) carry out demodulation and obtain d (t), then zero passage judgement is carried out to d (t) and obtain b (i), successfully receive sent information.

Frequency domain chaotic signal generator and subcarrier respective modules

Fig. 4 is the structure chart of frequency domain chaotic signal generator and subcarrier respective modules, and chaos sequence C (k) corresponding with the subcarrier of dynamic shift is produced by the chaos sequence generator that formula (1) is corresponding.

C(k)＝4C(k-1)-4C ²(k-1)k＝1,2,…，C(k)∈(0,1)(1)

Different with subcarrier corresponding relation from chaos sequence fixing in Fig. 2, subcarrier shift unit in Fig. 4 dynamically to match with subcarrier to chaos sequence C (k) and modulates, and this pair relationhip is determined jointly by subcarrier shift unit and frequency band mapping graph.Wherein, frequency spectrum mapping graph is that the frequency spectrum service condition that cognitive radio system perception surrounding spectrum situation obtains obtains:

After obtaining spectrum information, according to frequency band mapping graph to idle sub-carrier with cycle T _sScarry out dynamic shift, shift rule can be expressed as a shift matrix a N _nC× N _nCmatrix, wherein, N _nCfor the used number of sub carrier wave that cognitive radio system detects, this matrix is N by a dimension _nCthe chaos sequence C of × 1 _mk () determines, along with C _mthe Dynamic iterations of (k), matrix dynamically changes thereupon.In practical communication process, assailant, in order to find the corresponding relation of correct chaos sequence and subcarrier, needs to attempt all possibilities, this complexity is O (N _nC! ).Fig. 5 is an example of subcarrier shift unit.

Subcarrier shift unit

a transformation matrix, therefore every a line and each row all only have a nonzero element " 1 ".By to chaos sequence C _mk the sequence from small to large of (), can obtain the chaos sequence C sorted _mSortk (), by C _m(k) and C _mSortk () can generate simultaneously be one can by C _mk () is transformed to C _mSortthe matrix of (k), conversion expression formula is:

$C_{MSort}\left(k\right)=M_{N_{NC}}{C}_M\left(k\right)---\left(3\right)$

Can be obtained by (3):

$M_{N_{NC}}=f_S\left(C_{MSort}\right(k){\[C_M\left(k\right)\]}^{-1})---\left(4\right)$

In (4), ${\[C_M\left(k\right)\]}^{-1}=(\frac{1}{C_M\left(1\right)},\frac{1}{C_M\left(2\right)},...,\frac{1}{C_M\left(N_{NC}\right)}),$ Function f _s() is defined as:

Above-mentioned B _i,jthe element of the i-th row jth row of matrix B, AA represents a random matrix, herein for illustration of f _sthe definition of (), A _i,jthe element of the i-th row jth row of representing matrix A;

In Figure 5, N _nC=4, C _m=[0.10,0.98 ,-0.92 ,-0.69] ^t, by C _marrange from small to large, can C be obtained _mSort=[-0.92 ,-0.69,0.10,0.98] ^t, wherein () ^tthe transposition of representing matrix.In conjunction with (4) and (5), shift matrix M can be generated ₄:

$M_4=\left[\begin{array}{cccc}0& 0& 1& 0\\ 0& 0& 0& 1\\ 1& 0& 0& 0\\ 0& 1& 0& 0\end{array}\right]---\left(6\right)$

Then M is used ₄chaos sequence C (k) is shifted.C=[c in the present embodiment ₁, c ₂, c ₃, c ₄] ^t, can obtain:

C _S,1＝M ₄C＝[c3,c4,c1,c2] ^T(7)

Due to C _mk () by embodiment formula (1) Dynamic iterations, just can change once at regular intervals, also dynamic change thereupon, makes assailant be difficult to obtain subcarrier displacement rule, significantly enhances the fail safe of transmission data.

After have passed through subcarrier shift unit, OFDM subcarrier-modulated is carried out to chaos sequence.At interpolation Cyclic Prefix, serial/parallel conversion and will chaotic signal c (t) be produced after low pass filter.

$c\left(t\right)=\underset{k=1}{\overset{N}{\Σ}}C\left(k\right)a\left(k\right)e^{j2\mathrm{\π}k\mathrm{\Δ}ft}p\left(t\right)---\left(8\right)$

Wherein N represents total chaos sequence length, and C (k) represents the chaos sequence that kth item is produced by chaos sequence generator; K Δ f represents a kth subcarrier, wherein t _sfor the symbol period of OFDM; The unit height square wave of p (t) to be width a be symbol period.

Frequency domain chaos cognitive radio system transceiver

In the middle of the frequency domain chaos cognitive radio system be shifted based on subcarrier, the binary bits b (t) of BPSK to input system is used to modulate, and be multiplied with chaotic signal c (t) of OFDM modulation and obtain s (t), s (t) can be expressed as:

$s\left(t\right)=b\left(t\right)c\left(t\right)=\left\{\begin{array}{cc}+c\left(t\right),if& b\left(t\right)=+1\\ -c\left(t\right),if& b\left(t\right)=-1\end{array}\right.---\left(9\right)$

Through carrier wave cos (2 π f _ct), after modulation, signal is sent to AWGN (AdditiveWhiteGaussianNoise) channel.

At receiving terminal, receive the signal expression of t:

r(t)＝s(t)+n(t)(10)

Wherein, n (t) is average is 0, and variance is noise signal.C (t) is generated with identical flow process, r (t) and c at receiving terminal ^*t () obtains d (t) after carrying out demodulation:

d(t)＝r(t)c ^*(t)＝b(t)|c(t)| ^*+n(t)c ^*(t)(11)

Then the estimated value that zero passage judgement obtains information bit is carried out to d (t) complete communication process.

Performance evaluation

By knowing above, the corresponding relation dynamically changing chaos sequence and subcarrier is shifted except sub-carrier in such as Fig. 5, can also realize by being shifted to chaos sequence C (k).Conveniently mathematical expression, takes to be shifted to chaos sequence.In the diagram, suppose can obtain:

$C_S\left(k\right)=M_{N_{NC}}C\left(k\right)---\left(12\right)$

By Fig. 4 and Fig. 5, c _st () is by C _sk () obtains through IFFT (InverseFastFourierTransform) process, therefore

$c_S\left(t\right)=\sqrt{N_{NC}}{D}_{N_{NC}}^{-1}{C}_S\left(k\right)=\sqrt{N_{NC}}{D}_{N_{NC}}^{-1}{M}_{N_{NC}}C\left(k\right)---\left(13\right)$

Wherein the energy normalized factor, be dimension be N _nC× N _nCdiscrete Fourier transform (DFT).

$W_{N_{NC}}^i=\exp (\frac{-2\mathrm{\π}j}{N_{NC}}\·i),j=\sqrt{-1},i=1,2,...{(N_{NC}-1)}^2---\left(15\right)$

Suppose that chaos sequence can realize synchronously completely, the energy of each chaos bit is expressed as E _b, the signal to noise ratio (Signal-to-NoiseRatio, SNR) of the every bit so received is wherein E _bcan be obtained by following formula:

$\begin{array}{c}{E}_b=\underset{k=1}{\overset{N_{NC}}{\Σ}}{\left|c_S\left(t\right)\right|}^2=\underset{k=1}{\overset{N_{NC}}{\Σ}}\left|c_S^H\left(t\right)c_S\left(t\right)\right|\\ =\underset{k=1}{\overset{N_{NC}}{\Σ}}\left|N_{NC}{C}^H\left(k\right)M_{N_{NC}}^H{\left(D_{N_{NC}}^{-1}\right)}^H{D}_{N_{NC}}^{-1}XC\left(k\right)\right|\end{array}---\left(16\right)$

Wherein () ^hhermite transposition (HermitianTranspose), be the shift matrix of transmitting terminal, X is the shift matrix of receiving terminal.Can be obtained by formula (14):

$N_{NC}\·{\left(D_{N_{NC}}^{-1}\right)}^H\·D_{N_{NC}}^{-1}=E_{N_{NC}}---\left(17\right)$

Wherein be dimension be N _nCunit matrix.Based on formula (17), can be by formula (16) abbreviation:

$E_b=N_{NC}\·E\[\left|C^H\left(k\right)M_{N_{NC}}^{H}XC\left(k\right)\right|\]---\left(18\right)$

Wherein E () is mathematic expectaion operator.Conditional bit error rates (the BitErrorRate of convolution (18) and BPSK system, BER) formula, suppose that binary data is uniformly distributed, frequency domain chaos cognitive radio system based on subcarrier displacement can be obtained in the BER expression formula of awgn channel:

${\mathrm{BER}}_{AWGN}=Q\left(\sqrt{\frac{2N_{NC}\·E\[\left|C^H\left(k\right)M_{N_{NC}}^{H}XC\left(k\right)\right|\]}{N_0}}\right)---\left(19\right)$

Wherein Q () is Gauss Q function, because validated user has shift matrix information, so at validated user receiving terminal, in formula (19) the BER expression formula based on the frequency domain chaos cognitive radio system of subcarrier displacement under normal sight can be obtained:

${\mathrm{BER}}_{Normal}=Q\left(\sqrt{\frac{2N_{NC}\·E\[{\left|C\left(k\right)\right|}^2\]}{N_0}}\right)---\left(20\right)$

Next information leakage (Informationleakage) analysis can be carried out to the frequency domain chaos cognitive radio system be shifted based on subcarrier.Suppose 0 and 1 equal-probability distribution in transmission data, so transmitting terminal transmission data X and the data Y that recovers at receiving terminal of assailant _ebetween mutual information be:

I _k(Y _E；X)＝H _k(Y _E)-H _k(Y _EX _E)＝1+p _klog ₂p _k+(1-p _k)log ₂(1-p _k)(21)

Wherein H () is comentropy operator, p _kthe BER of the assailant's receiving terminal obtained by (19).Suppose N in the frequency domain chaos cognitive radio system based on subcarrier displacement _nCindividual subcarrier is independently, and so the information leakage of this system can be expressed as:

$L=\frac{1}{N_{NC}}\underset{k=1}{\overset{N_{NC}}{\Σ}}{I}_k(Y_E;X)---\left(22\right)$

In order to verify the performance of the frequency domain chaos cognitive radio system based on subcarrier displacement, we emulate the communication process of this system.In simulations, available free sub-carrier number N _nC={ 16,64,256}, in the enterprising Serial Communication emulation of awgn channel.Fig. 6 gives the performance curve that the frequency domain chaos cognitive radio system BER based on subcarrier displacement proposed by the invention and information leakage change with SNR.

Fig. 6 is System performance profiles figure, (a) BER performance curve, the information leakage performance curve of (b) listener-in receiving terminal.

Because legal user knows all key parameters used at transmitter, so the BER expression formula of validated user is (20).Can be obtained by Fig. 6 (a), validated user theoretical curve and simulation curve overlap.Along with the increase of number of usable subcarriers, BER performance does not have significant change, and the system in Fig. 6 (a) is due to channel estimation errors, along with communicator carrier number increases BER degradation, compared with the system in Fig. 6 (a), the frequency domain chaos cognitive radio system based on subcarrier displacement can provide more stable proper communication.The BER of listener-in is apparently higher than validated user proper communication, and along with the increase of number of usable subcarriers, BER can increase gradually.

Produce such phenomenon be because value be different from E [C ²(k)], be destroyed at listener-in's receiving terminal detector demodulates signal out, be difficult to correct judgement.Such as, at the E [C of the chaos sequence of the chaos sequence maker generation provided by formula (1) ²(k)] and when being 0.48 and 0.024 respectively, gap is fairly obvious, substitutes into the BER performance curve that formula (19) and (20) can draw great disparity respectively, conforms to simulation result in Fig. 6.Because error rate during recovery information is too high, unless listener-in obtains correct shift matrix information, otherwise the information that cannot be transmitted within the system.

Suppose that listener-in knows the system information of all keys except the consistent relationship between chaos sequence and subcarrier, utilize formula (22), emulate the information leakage of the frequency domain chaos cognitive radio system be shifted based on subcarrier and traditional frequency domain chaos cognitive radio system listener-in receiving terminal, Fig. 6 (b) is simulation result.Can be obtained by Fig. 6 (b), under this assumed condition, the system that the frequency domain chaos cognitive radio system based on subcarrier displacement significantly can reduce the information leakage of listener-in's receiving terminal traditional then has obvious information leakage.

Obviously, the above embodiment of the present invention is only for example of the present invention is clearly described, and is not the restriction to embodiments of the present invention.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here exhaustive without the need to also giving all execution modes.All any amendments done within the spirit and principles in the present invention, equivalent to replace and improvement etc., within the protection range that all should be included in the claims in the present invention.

Claims (3)

1. the frequency domain chaos cognitive radio system based on subcarrier displacement, comprise transmitting terminal and receiving terminal, it is characterized in that, at transmitting terminal, first generate chaos sequence C (k) by chaos sequence generator, then realize chaos sequence C (k) by subcarrier respective modules dynamically to change with subcarrier corresponding relation, chaotic signal c (t) based on frequency domain is generated again by frequency domain chaos signal generator, input data information obtains b (t) through BPSK modulation, b (t) is modulated into s (t) by c (t), then the wireless channel of available band is sent to by carrier modulation, at receiving terminal, after carrier coherent demodulating, chaotic signal c (t) based on frequency domain is generated equally by frequency domain chaos signal generator, chaotic signal c (t) after synchronization to received signal r (t) carry out demodulation and obtain d (t), then the estimated value that zero passage judgement obtains information bit is carried out to d (t) successfully receive sent information.

2. the frequency domain chaos cognitive radio system based on subcarrier displacement according to claim 1, is characterized in that, described subcarrier respective modules realizes the concrete mode that chaos sequence C (k) dynamically changes with subcarrier corresponding relation and is:

Subcarrier shift unit dynamically to match with subcarrier to chaos sequence C (k) and modulates, and this pair relationhip is determined jointly by subcarrier shift unit and frequency band mapping graph;

Wherein, frequency spectrum mapping graph is that the frequency spectrum service condition that cognitive radio system perception surrounding spectrum situation obtains obtains:

Be map the C (k) of input, when the individual sub-carrier occupancy of kth, its frequency a (k) sets to 0, and when a kth subcarrier is idle, its frequency a (k) is then set to 1,

Make the signal after IFFT only comprise idle frequency component, after obtaining frequency spectrum service condition information, according to frequency band mapping graph to idle sub-carrier with cycle T _sScarry out dynamic shift, after displacement, obtain the chaos sequence of one section of particular arrangement, use sequence C (k) and formula (3)-(6), generate and based on after chaotic signal c (t) of frequency domain, communication information b (t) is modulated, make listener-in be difficult to crack communication system thus obtaining communication information, dynamic shift Rule Expression is a shift matrix a N _nC× N _nCmatrix, wherein, N _nCfor the used number of sub carrier wave that cognitive radio system detects, k=1,2 ..., N _nC; Shift matrix be N by a dimension _nCthe chaos sequence C of × 1 _mk () determines, along with C _mthe Dynamic iterations of (k), matrix dynamically changes thereupon;

Described that every a line and each row all only have a nonzero element " 1 ", by chaos sequence C _mk the sequence from small to large of (), obtains the chaos sequence C sorted _mSortk (), by C _m(k) and C _mSortk () generates and be one can by C _mk () is transformed to C _mSortthe matrix of (k), conversion expression formula is:

$C_{MSort}\left(k\right)=M_{N_{NC}}{C}_M\left(k\right)---\left(3\right)$

Can be obtained by (3):

$M_{N_{NC}}=f_S\left(C_{MSort}\right(k\left){\[C_M\left(k\right)\]}^{-1}\right)---\left(4\right)$

In (4), ${\[C_M\left(k\right)\]}^{-1}=(\frac{1}{C_M\left(1\right)},\frac{1}{C_M\left(2\right)},...,\frac{1}{C_M\left(N_{NC}\right)}),$ Function f _s() is defined as:

Above-mentioned B _i,jthe element of the i-th row jth row of matrix B, AA represents a random matrix, herein for illustration of f _sthe definition of (), A _i,jthe element of the i-th row jth row of representing matrix A;

Due to chaos sequence C _mk () by chaos sequence generator Dynamic iterations, just can change once at regular intervals, also dynamic change thereupon, makes assailant be difficult to obtain subcarrier displacement rule, significantly enhances the fail safe of transmission data;

After dynamic shift process, OFDM subcarrier-modulated is carried out to chaos sequence; At interpolation Cyclic Prefix, serial/parallel conversion and will chaotic signal c (t) be produced after low pass filter;

$c\left(t\right)=\underset{k=1}{\overset{N}{\Σ}}C\left(k\right)a\left(k\right)e^{j2\mathrm{\π}k\mathrm{\Δ}ft}p\left(t\right)---\left(6\right)$

Wherein N represents total chaos sequence length, and C (k) represents the chaos sequence that kth item is produced by chaos sequence generator; K Δ f represents a kth subcarrier, wherein t _sfor the symbol period of OFDM; The unit height square wave of p (t) to be width a be symbol period.

3. the frequency domain chaos cognitive radio system based on subcarrier displacement according to claim 2, is characterized in that,

In the middle of the frequency domain chaos cognitive radio system be shifted based on subcarrier, the binary bits b (t) of BPSK to input system is used to modulate, and be multiplied with chaotic signal c (t) of OFDM modulation and obtain s (t), s (t) is expressed as:

$s\left(t\right)=b\left(t\right)c\left(t\right)=\left\{\begin{array}{c}+c\left(t\right),ifb\left(t\right)=+1\\ -c\left(t\right),ifb\left(t\right)=-1\end{array}\right.---\left(9\right)$

Through carrier wave cos (2 π f _ct), after modulation, signal is sent to awgn channel;

At receiving terminal, receive the signal expression of t:

r(t)＝s(t)+n(t)(10)

Wherein, n (t) is average is 0, and variance is aWGN noise signal, generates c (t), r (t) and c at receiving terminal with flow process identical with transmitting terminal ^*t () obtains d (t) after carrying out demodulation:

d(t)＝r(t)c ^*(t)＝b(t)|c(t)| ^*+n(t)c ^*(t)(11)

Then the estimated value that zero passage judgement obtains information bit is carried out to d (t) complete communication process.