CN104618297A - OFDM-DCSK communication system - Google Patents

Abstract

The invention discloses an OFDM-DCSK (Orthogonal Frequency Division Multiplexing-Differential Chaos Shift Keying) communication system and relates to the wireless communication field. The purpose of the invention is that the data rate is increased in the OFDM-DCSK communication system to solve the delay problem of RF (radio frequency). As an irrelevant chaos communication solution, all subcarriers are divided into several groups, chaos reference sequences are transmitted by the central subcarrier in each group, and modulated data streams are transmitted by the subcarriers in the residual groups. Thus, in comparison with a traditional DCSK system, the spectrum utilization rate is improved by a transmitting structure. The received data on a receiving end isn't demodulated by a radio frequency delay circuit, so that a convenient condition is provided to the system in practical application. The system is applied to wireless communication occasions.

Description

OFDM-DCSK communication system

Technical field

The present invention relates to wireless communication field.

Background technology

Because chaotic signal has following characteristic: aperiodicity, certainty, noise like, broadband and be easy to produce.Chaotic communication system is studied widely in recent years, in the past few years, propose a series of chaotic modulation scheme successively, wherein difference chaotic offset keying (DCSK) is due to its good noise robustness with simply send demand, is best suited for being applied to actual modulation system.See document 1 disclosed in 2011: document 2 " Exact analytical bit error rates for multiple access chaos-based communication systems " disclosed in " Performance analysis ofdifferential chaotic shift keying communications in MIMO systems " and 2004;

In order to improve the availability of frequency spectrum of DCSK system, document 3 disclosed in 2012: propose efficient DCSK (HE-DCSK) in " High-efficiencydifferential-chaos-shift keying scheme for chaos-based noncoherent communication ".But the radio frequency of its receiving terminal (RF) delay circuit is not easy to be applied in CMOS technology.

At document 4 disclosed in 2011: document 5 disclosed in " A novel differential chaos shift keying modulation scheme " and 2012: in " Design of a high-data-rate differential chaos-shift keyingsystem ", author proposes the difficult problem that the multiplexing DCSK of code (CS-DCSK) goes to overcome RF time delay.Reference signal and information signal are separated with chaotically coding sequence by walsh sequence respectively.H.Yang and G.Jiang puts forward RM-DCSK scheme to be reduced complexity and improves information rate.

Disclosed in 2010, document 6 " M-DCSK-based chaotic communications in MIMO multipathchannels with no channel state information " have studied Mary DCSK.Improve information rate as multi-level DCSK, Mary DCSK system, but compared with DCSK system, this system is too complicated.

Document 7 disclosed in 2013: in " Design and analysis of a multi-carrier differential chaos shiftkeying communication system ", author proposes multicarrier DCSK (MC-DCSK) technology and improves energy efficiency, solve RF and demonstrate problem, and improve BER performance.

Document 8 disclosed in 2012: in " OFDM-based chaotic spread spectrum communications withhigh bandwidth efficiency ", author proposes the incoherent chaotic communication system based on OFDM (OFDM).

Document 9 disclosed in 2014: in " An OFDM-based chaotic DSSS communication system withM-PSK modulation ", author modulates in conjunction with Mary phase shift keying, based on OFDM technology, propose a kind of relevant chaos direct sequence spread spectrum communication system.

Chaotic communication is applied to the feasibility document 10 disclosed in 2009 in multiple-input and multiple-output (MIMO) channel: confirm in " Space-time coding and processing with differential chaos shift keying scheme ", wherein uses Alamouti code as Space-Time Block Coding (STBC).Then document 11 disclosed in 2011: " Performance analysis of differential chaotic shift keying communications in MIMOsystems ", the authors' analysis BER performance of MIMO-DCSK.But, in order to STBC decoding, need extra hardware circuit to estimate channel condition information (CSI).In order to solve the complexity of CSI problem and reduction realization, author is at document 12 disclosed in 2013: the STBC-DCSK scheme proposing simulation in " One analog STBC-DCSK transmission scheme notrequiring channel state information ", it considers the mode of two or three transmitting antennas and single reception antenna.

Many documents propose the method for analyzing performance of DCSK system, document 13 disclosed in 2012: " Ageneralized BER prediction method for differential chaos shift keying system throughdifferent communication channels ", document 14 disclosed in 2010: " Design and simulation ofa cooperative communication system based on DCSK/FM-DCSK ", the disclosed document 15 of 2000: " Performance analysis of correlation-based communication schemes utilizing chaos ".Gaussian approximation method (GA) can estimate BER performance accurately under the condition that spreading factor is larger.But when spreading factor is less, GA shows the estimation of low precision.Accurate method provides in document 13.Method based on chaos Energy distribution can estimate the BER performance of DCSK system accurately in additive white Gaussian noise awgn channel, Rice channel and Rayleigh channel.Certainly also have many documents to pay close attention to performance evaluation that DCSK system is applied in collaboration communication field, such as document 16 disclosed in 2011: document 17 " Performance of MIMO relay DCSK-CD systems over nakagami fading channels " disclosed in " Performance of DCSK cooperativecommunication systems over multipath fading channels " and 2013.

Summary of the invention

The present invention is to increase data rate in OFDM-DCSK system, solving RF latency issue, thus provides a kind of OFDM-DCSK communication system.

The signal transmitting method of OFDM-DCSK communication system is:

Step one, under the transmission of every frame OFDM-DCSK, original information bits b=[b ₀, b ₁..., b _{m × L}] { 0,1} modulates through BPSK ∈, obtains the modulation sequence d of serial; M+1 is sub-carrier number;

Step 2, the modulation sequence d of serial is carried out serial/parallel changing, obtain L group Parallel Sequence; For l group subcarrier, Parallel Sequence is expressed as m=1,2 ..., M; L=1,2 ..., L; β is spreading factor;

Step 3, employing chaos reference sequences x ^lrespectively by information bit spread to and be assigned on m subcarrier of l group;

Described chaos reference sequences x ^lproduced by 2 rank Chebyshev inequalities (CPF);

Wherein: 2 rank Chebyshev inequalities are:

$x_{j+1}=1-2x_j^2,(-1<x_j<1,\&NotEqual;\{\mathrm{0,}\&PlusMinus;0.5\left\}\right)$

For l group, order represent chaos reference sequences;

Step 4, by Parallel Sequence through IFFT conversion and parallel/serial conversion after, be sent in wireless channel;

The signal acceptance method of OFDM-DCSK communication system is:

Step 5, receiving terminal be Received signal strength r from wireless channel, and after serial/parallel conversion and FFT conversion, obtains Parallel Sequence;

Step 6, decode to often organizing sequence respectively, the decode procedure often organizing subcarrier is identical, and for first group of subcarrier, its coding/decoding method is:

First, central subcarrier is stored in matrix P, and all the other M data-signal is stored in the 2nd matrix S; Provide respectively in matrix P and S formula below:

$P=(x_0^1+n_0^1,x_1^1+n_1^1,...,x_{\mathrm{\&beta;}-1}^1+n_{\mathrm{\&beta;}-1}^1),---\left(1\right)$

$S=\left(\begin{array}{ccc}{d}_1^1{x}_0^1+n_{\mathrm{1,0}}^1& ...& d_1^1{x}_{\mathrm{\&beta;}-1}^1+n_{1,\mathrm{\&beta;}-1}^1\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ d_M^1{x}_0^1+n_{M,0}^1& ...& d_M^1{x}_{\mathrm{\&beta;}-1}^1+n_{M,\mathrm{\&beta;}-1}^1\end{array}\right),---\left(2\right)$

Wherein: for being added to a jth sample of AWGN in reference signal, for being added to a jth sample of the AWGN in first group of m subcarrier;

After the β section time, all samples are all stored in an OFDM-DCSK frame, and decoding step is activated, and finally, M bit of transmission is decoded by the symbol parallel of compute matrix product;

Wherein: × be multiplication of matrices, ' transposition of representing matrix;

Step 7, decoded signal is carried out parallel/serial conversion, and carry out demodulation, obtain original information bits b, and export.

The concrete grammar that M the bit sent described in step 6 is decoded by the symbol parallel of compute matrix product is:

Steps A, initial m=1;

Step B, according to formula:

$D_m^1={\mathrm{\&Sigma;}}_{j=0}^{\mathrm{\&beta;}-1}(d_j^1{x}_j^1+n_{m,j}^1)(x_j^1+n_j^1)$

Calculating observation signal and

Step C, by observation signal and compare with threshold value 0:

Complete the decoding to this group sequence;

Step D, judge whether m=M, if so, then terminate; If not, then execution step B is returned.

The DCSK system of the present invention's ratio, 1) capacity usage ratio DBR has been brought up to M/ (M+1) from 1/2, wherein each information signal of DCSK system needs a reference signal, and OFDM-DCSK signal M bit shares a reference signal; 2) simulation results show, under the identical β factor, the performance of OFDM-DCSK system is better; 3) the RF latency issue being present in DCSK system, HE-DCSK and CS-DCSK system is solved.Compared to ofdm system, receiving terminal without the need to channel estimating simultaneously at transmitting terminal also without the need to CSI feedback.Compared with the OFDM-CSK in document 8, the present invention can obtain better BER performance in 2 footpath Rayleigh channels.It is easier to be applied to reality.

Accompanying drawing explanation

Fig. 1 be OFDM-DCSK l group (l=1,2 ..., L) m (m=1,2 ..., M) and the signal format schematic diagram of carrier wave;

Fig. 2 is the transmitting terminal signal flow schematic diagram of OFDM-CDMA;

Fig. 3 is the receiving end signal schematic flow sheet of OFDM-CDMA;

Embodiment

Embodiment one, composition graphs 1 to Fig. 3 illustrate this embodiment, OFDM-DCSK communication system,

The signal transmitting method of OFDM-DCSK communication system is:

Step one, under the transmission of every frame OFDM-DCSK, original information bits b=[b ₀, b ₁..., b _{m × L}] { 0,1} modulates through BPSK ∈, obtains the modulation sequence d of serial; M+1 is sub-carrier number;

Step 2, the modulation sequence d of serial is carried out serial/parallel changing, obtain L group Parallel Sequence; For l group subcarrier, Parallel Sequence is expressed as m=1,2 ..., M; L=1,2 ..., L; β is spreading factor;

Step 3, employing chaos reference sequences x ^lrespectively by information bit spread to and be assigned on m subcarrier of l group;

Described chaos reference sequences x ^lproduced by 2 rank Chebyshev inequalities (CPF);

Wherein: 2 rank Chebyshev inequalities are:

$x_{j+1}=1-2x_j^2,(-1<x_j<1,\&NotEqual;\{\mathrm{0,}\&PlusMinus;0.5\left\}\right)$

For l group, order represent chaos reference sequences;

Step 4, by Parallel Sequence through IFFT conversion and parallel/serial conversion after, be sent in wireless channel;

The signal acceptance method of OFDM-DCSK communication system is:

Step 5, receiving terminal be Received signal strength r from wireless channel, and after serial/parallel conversion and FFT conversion, obtains Parallel Sequence;

Step 6, decode to often organizing sequence respectively, the decode procedure often organizing subcarrier is identical, and for first group of subcarrier, its coding/decoding method is:

First, central subcarrier is stored in matrix P, and all the other M data-signal is stored in the 2nd matrix S; Provide respectively in matrix P and S formula below:

$P=(x_0^1+n_0^1,x_1^1+n_1^1,...,x_{\mathrm{\&beta;}-1}^1+n_{\mathrm{\&beta;}-1}^1),---\left(1\right)$

$S=\left(\begin{array}{ccc}{d}_1^1{x}_0^1+n_{\mathrm{1,0}}^1& ...& d_1^1{x}_{\mathrm{\&beta;}-1}^1+n_{1,\mathrm{\&beta;}-1}^1\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ d_M^1{x}_0^1+n_{M,0}^1& ...& d_M^1{x}_{\mathrm{\&beta;}-1}^1+n_{M,\mathrm{\&beta;}-1}^1\end{array}\right),---\left(2\right)$

Wherein: for being added to a jth sample of AWGN in reference signal, for being added to a jth sample of the AWGN in first group of m subcarrier;

After the β section time, all samples are all stored in an OFDM-DCSK frame, and decoding step is activated, and finally, M bit of transmission is decoded by the symbol parallel of compute matrix product;

Wherein: × be multiplication of matrices, ' the transposition of representing matrix;

Step 7, decoded signal is carried out parallel/serial conversion, and carry out demodulation, obtain original information bits b, and export.

The concrete grammar that M the bit sent described in step 6 is decoded by the symbol parallel of compute matrix product is:

Steps A, initial m=1;

Step B, according to formula:

$D_m^1={\mathrm{\&Sigma;}}_{j=0}^{\mathrm{\&beta;}-1}(d_j^1{x}_j^1+n_{m,j}^1)(x_j^1+n_j^1)$

Calculating observation signal and

Step C, by observation signal and compare with threshold value 0:

Complete the decoding to this group sequence;

Step D, judge whether m=M, if so, then terminate; If not, then execution step B is returned.

Principle: signal format and chaos generator

According to 3GPP technical report, for given transmission bandwidth (B _w), the number of sub carrier wave (N of OFDM _sub) FFT should be less than count (N _fft).Make N _pilotfor the number of pilot sub-carrier (reference subcarrier), N _datafor the data (N of data subcarrier _pilot+ N _data=N _sub).

Inspired by the comb pilot frequency mode of OFDM, in order to improve data rate, solving RF problem, the present invention proposes a kind of scheme of novel DCSK communication system, called after OFDM-DCSK.

For incoherent DCSK communication system, reference signal must be transmitted and replace frequency pilot sign.Therefore, the pilot sub-carrier in OFDM may be used for the reference signal transmitting OFDM-DCSK system.

For the OFDM-DCSK scheme proposed, first by N _subindividual subcarrier is divided into L group, often total M+1 the subcarrier (N of group _sub=L × (M+1)).Central subcarrier transmission chaos reference channel often in group, all the other M carrier wave transmission of informations.Illustrate in FIG OFDM-DCSK l group (l=1,2 ..., L) m (m=1,2 ..., M) and the signal format of carrier wave, wherein represent l group m subcarrier jth (j=0,1 ..., β-1) and element; represent a jth element of the chaos reference signal on the central subcarrier of l group; β is spreading factor.

Produce chaos sequence by 2 rank Chebyshev inequalities (CPF), wherein 2 rank Chebyshev inequalities are: $x_{j+1}=1-2x_j^2,(-1<x_j<1,\&NotEqual;\{\mathrm{0,}\&PlusMinus;0.5\left\}\right)$

For l group, order represent chaos reference sequences.Different chaos sequences is produced by different initial values.

In addition, all chaos sequences are all normalized, and therefore their average is zero, and mean-square value is 1, E (x _j)=0 and E (x ² _j)=1.Under the condition of large spreading factor, two chaos sequence R _land R _kcorrelation can be approximated to be E [R _kr _l]=β as k=l, E [R _kr _l]=0 as k ≠ l, wherein R _kr _lrepresent the dot product of two chaos vectors.

Transmitting terminal

The sending end structure of OFDM-CDMA as shown in Figure 2.For the transmission time of every frame OFDM-DCSK, information bit b=[b ₀, b ₁..., b _{m × L}] { 0,1} is modulated to d by BPSK to ∈.Then the d of serial is converted into Parallel Sequence.For l group subcarrier, Parallel Sequence is expressed as

In addition, information bit by chaos reference sequences x ^lspread to and be assigned on m subcarrier of l group.Finally, Parallel Sequence is converted into serial sequence through IFFT and is sent in wireless channel.Contemplated by the invention additive white noise channel (AWGN).

Receiving terminal:

Receive structure as shown in Figure 3.Receiving terminal of the present invention compared to DCSK scheme without the need to RF delay circuit, compared to ofdm system without the need to channel estimating and equalization.What the present invention utilized is noncoherent detection method.The decode procedure of different group subcarrier is similar.Therefore, we only need pay close attention to first group of subcarrier hereinafter.

First, central subcarrier is stored in matrix P, and all the other M data-signal is stored in the 2nd matrix S.Provide respectively in matrix P and S formula below:

$P=(x_0^1+n_0^1,x_1^1+n_1^1,...,x_{\mathrm{\&beta;}-1}^1+n_{\mathrm{\&beta;}-1}^1),---\left(1\right)$

$S=\left(\begin{array}{ccc}{d}_1^1{x}_0^1+n_{\mathrm{1,0}}^1& ...& d_1^1{x}_{\mathrm{\&beta;}-1}^1+n_{1,\mathrm{\&beta;}-1}^1\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;\\ d_M^1{x}_0^1+n_{M,0}^1& ...& d_M^1{x}_{\mathrm{\&beta;}-1}^1+n_{M,\mathrm{\&beta;}-1}^1\end{array}\right),---\left(2\right)$

Wherein for being added to a jth sample of AWGN in reference signal, for being added to a jth sample of the AWGN in first group of m subcarrier.

After the β section time, all samples are all stored in an OFDM-DCSK frame, and decoding step is activated.Finally, M bit of transmission is decoded by the symbol parallel of compute matrix product.

Wherein × and be multiplication of matrices, ' the transposition of representing matrix.In fact, formula (3) is equal to a few step below:

1), initial m=1;

2), calculating observation signal and:

$D_m^1={\mathrm{\&Sigma;}}_{j=0}^{\mathrm{\&beta;}-1}(d_j^1{x}_j^1+n_{m,j}^1)(x_j^1+n_j^1);$

3), compare with threshold value 0;

4) if m=M, stop; Otherwise rebound (2).

Performance evaluation:

In this section, first we calculate the capacity usage ratio of the OFDM-DCSK of proposition.Then give under awgn channel, utilize the bit error rate performance of Gaussian approximation to derive.

A, capacity usage ratio

Compared to DCSK system, new system enhancement capacity usage ratio.Make E _dataand E _refrepresent the in information sequence of transmission and the energy of reference sequences respectively.For traditional DCSK system, the bit energy E of transmission _bcan be expressed as:

E _b＝E _data+E _ref(4)

Assuming that information and reference sequences have identical energy, wherein:

$E_{\mathrm{data}}=E_{\mathrm{ref}}={\mathrm{\&Sigma;}}_{j=0}^{\mathrm{\&beta;}-1}{x}_j^2.$

Secondly, for a given bit, energy is sent:

$E_b=2E_{\mathrm{data}}=2{\mathrm{\&Sigma;}}_{j=0}^{\mathrm{\&beta;}-1}{x}_j^2.$

In our OFDM-DCSK system, each subcarrier group, a reference energy E _refsent bit by M to share.

Therefore, for given bit, send energy:

$E_b=E_{\mathrm{data}}+E_{\mathrm{ref}}/M=\frac{M+1}{M}{E}_{\mathrm{data}};$

The ratio DBR of definition information energy and bit energy is:

$\mathrm{DBR}=\frac{E_{\mathrm{data}}}{E_b}---\left(5\right)$

Traditional DCSK system, DBR is 1/2, this means the bit energy E of 50% _bfor sending reference signal.And for OFDM-DCSK system, DBR is M/ (M+1).As M>10, the energy of reference signal is less than gross energy E _b10%.Therefore the capacity usage ratio ratio DCSK system of OFDM-DCSK system adds.

B, BER derive:

To derive under awgn channel the BER performance of OFDM-DCSK.Each subcarrier group has identical structure, and also has identical structure with each information carrier in group, therefore, only need pay close attention to l (l=1,2 ..., L) carrier wave set m (m=1,2 ..., M) and information carrier.In derivation, employ the method for Gaussian approximation (GA), it is to very effective under large spreading factor condition.

Therefore can be derived by the average and variance calculating them performance.Due to the initial value sensitiveness of chaos sequence, we can think that the different chaos sequence that different initial condition produces is independent of each other.In addition, according to document [23], Gaussian noise and chaos sequence are also independent of each other.The chaos sequence produced by CPF is normalized, and having average is 0, and mean-square value is the characteristic of 1, and under large spreading factor condition, the correlation of two different chaos sequences can be expressed as E [R _kr _l]=0 is as k ≠ l.

L group m observation signal be expressed as:

$D_m^l=\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}(d_j^l{x}_j^l+n_{m,j}^l)\&times;(x_j^l+n_j^l),---\left(6\right)$

Wherein with be two independently Gaussian noises, come from information bit and chaos reference bits respectively.

Formula (6) can be converted into simple form:

$D_m^l=\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{d}_j^l{x}_j^l{x}_j^l+\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{x}_j^l(d_j^l{n}_j^l+n_{m,j}^l)+\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{n}_j^l+n_{m,j}^l.---\left(7\right)$

In formula (7), Section 1 is useful signal, other two be all zero-mean additive noise interference.

Order be the transmission bit energy of information sequence given in l group carrier wave, can be expressed as:

$E_b^l=\frac{M+1}{M}\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{\left(x_j^l\right)}^2.---\left(8\right)$

Then, formula (7) just can be write as:

$D_m^l=d_j^l\frac{M}{M+1}{E}_b^l+W+Z,---\left(9\right)$

Wherein:

$W=\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{x}_j^l(d_j^l{n}_j^l+n_{m,j}^l)---\left(10\right)$

$Z=\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{n}_j^l{n}_{m,j}^l---\left(11\right)$

For given l group m subcarrier, average and variance as follows:

$E\left(D_m^l\right)=d_j^l\frac{M}{M+1}{E}_b^l,---\left(12\right)$

$\begin{array}{c}\mathrm{Var}\left(D_m^l\right)=E\left({\left(d_j^l\frac{M}{M+1}{E}_b^l\right)}^2\right)+E\left({\left(\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{x}_j^l{d}_j^l{n}_j^l\right)}^2\right)\\ +E\left({\left(\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{x}_j^l{n}_{m,j}^l\right)}^2\right)+E\left({\left(\underset{j=0}{\overset{\mathrm{\&beta;}-1}{\mathrm{\&Sigma;}}}{n}_j^l{n}_{m,j}^l\right)}^2\right)\\ -{\left(d_j^l\frac{M}{M+1}{E}_b^l\right)}^2.\end{array}---\left(13\right)$

Suppose with be zero-mean, power spectral density is N ₀the wideband A WGN of/2.Gaussian noise and chaos sequence are independently, and different chaos sequences is independent of each other, and therefore (13) can be reduced to:

$\mathrm{Var}\left(D_m^l\right)=\frac{M}{(M+1)}{E}_n^l{N}_0+\mathrm{\&beta;}{N}_0^2/4.---\left(14\right)$

Suppose that bit energy is a variable determined, utilize formula (12) and (14), can bit error rate performance be calculated:

$\begin{array}{c}\mathrm{BER}=\frac{1}{2}\mathrm{Pr}(D_m^l<0|d_m^l=+1)+\frac{1}{2}\mathrm{Pr}(D_m^l>0|d_m^l=-1)\\ =\frac{1}{2}\mathrm{erfc}\left(\frac{E\left(D_m^l\right)|d_m^l=+1}{\sqrt{2\mathrm{Var}\left(D_m^l\right)|d_m^l=+1}}\right)\\ =\frac{1}{2}\mathrm{erfc}\left(\frac{d_j^l\frac{M}{M+1}{E}_b^l}{\sqrt{\frac{M}{(M+1)}{E}_n^l{N}_0+2\mathrm{\&beta;}{N}_0^2/4}}\right)\\ =\frac{1}{2}\mathrm{erfc}\left({[2\frac{M+1}{M}\frac{N_0}{E_b}+{\left(\frac{M+1}{M}\right)}^2\frac{\mathrm{\&beta;}}{2}{\left(\frac{N_0}{E_b}\right)}^2]}^{-\frac{1}{2}}\right)\end{array}---\left(15\right)$

Wherein: $\mathrm{erfc}\left(x\right)=\frac{2}{\sqrt{\mathrm{\&pi;}}}{\&Integral;}_x^{\&infin;}{e}^{-{\mathrm{\&mu;}}^2}\mathrm{d\&mu;}$ It is error function.

Information bit due to other has above-mentioned identical structure, and therefore the BER performance of OFDM-DCSK can be described as:

$\begin{array}{c}{\mathrm{BER}}_{\mathrm{OFDM}-\mathrm{DCSK}}\\ =\frac{1}{2}\mathrm{erfc}\left({[2\frac{M+1}{M}\frac{N_0}{E_b}+{\left(\frac{M+1}{M}\right)}^2\frac{\mathrm{\&beta;}}{2}{\left(\frac{N_0}{E_b}\right)}^2]}^{-\frac{1}{2}}\right)\end{array}---\left(16\right)$

The present invention is in a kind of novel transmission structure of transmitting terminal design.Because chaotic signal is applicable to spread spectrum communication, therefore we pay close attention to multi-carrier direct sequence code division multiple access (MC-DS-DCSK).In addition, OFDM is a kind of special case of multicarrier.The key of decoding OFDM is the estimation of accurate channel parameter.The elementary tactics of OFDM channel estimating is that decision pilot channel estimating and Auxiliary Pilot Channel are estimated.Auxiliary Pilot Channel is estimated there are two kinds of fundamental modes here: block formula and comb.For comb pilot frequency mode, aiming symbol is distributed in data subcarrier.Generally speaking, guide subcarrier to be equally spaced on frequency domain, and guided vehicle proportion equal 1/8.The comb bootmode of above-mentioned OFDM gives us and inspires, and in order to increase data rate, solve RF latency issue, we have proposed a kind of new design of DCSK communication system, called after OFDM-DSCK.

In the present invention, at transmitting terminal, all subcarriers are divided into several groups (being assumed to L group).Often in group, have a subcarrier to transmit reference signal, and remaining subcarrier (assuming that M subcarrier) will carry data message.The program not only improves data rate, improves capacity usage ratio (because 1 reference signal can for M bit information), also solves RF problem.Then, the present invention supposes to export followed normal distribution distribution, utilizes the BER performance of system under the methods analyst of Gaussian approximation awgn channel.In addition, under AWGN and double rayleigh channel condition, the present invention gives a large amount of simulation results.Finally, the present invention compares BER performance expression and simulation result.

Compared with document 9, the solution of the present invention, is easier to be applied to reality without the need to chaos sequence generator at receiving terminal.Compared with document 8, all subcarriers divide in order to several groups by the present invention.At receiving terminal, the data of each group are recovered by the reference signal (at central subcarrier) of this group, and data all in document 8 all will be recovered by same reference signal (first subcarrier).FOR ALL WE KNOW, ofdm system can be considered to the system in a broadband.Each subcarrier forms a narrowband systems and adjacent subcarrier has identical channel gain.For awgn channel, the subcarrier of nearly all OFDM has similar channel gain, but under flat Rayleigh fading channel, different subcarriers has different gains.Therefore, all subcarriers are divided into several groups extremely important, can by the interferer signal detection of current group to data, this is similar to the concept of 3GPP LTE Resource Block very much.

Be different from document 7, the structure based on OFDM is used for DCSK system, the performance of system in fading channel can be improved.Unlike the system configuration in document 7, this invention takes typical OFDM structure in 3GPP LTE standard, this makes it be easier to apply in practice.

In the present invention, we are actual and analyze an efficient incoherent OFDM-DCSK system.We have studied the performance of system, and the BER expression formula of system under awgn channel of having derived.Simulation result and theoretical BER expression formula match.The DCSK system of ratio, 1) capacity usage ratio DBR has been brought up to M/ (M+1) from 1/2, wherein each information signal of DCSK system needs a reference signal, and OFDM-DCSK signal M bit shares a reference signal; 2) simulation results show, under the identical β factor, the performance of OFDM-DCSK system is better; 3) the RF latency issue being present in DCSK system, HE-DCSK and CS-DCSK system is solved.Compared to ofdm system, receiving terminal without the need to channel estimating simultaneously at transmitting terminal also without the need to CSI feedback.Compared with the OFDM-CSK in document 8, we can obtain better BER performance in 2 footpath Rayleigh channels.The present invention is easier to be applied to reality.

Claims (2)

1.OFDM-DCSK communication system, is characterized in that:

The signal transmitting method of OFDM-DCSK communication system is:

Step one, under the transmission of every frame OFDM-DCSK, original information bits b=[b ₀, b ₁..., b _{m × L}] { 0,1} modulates through BPSK ∈, obtains the modulation sequence d of serial; M+1 is sub-carrier number quantity;

Step 2, the modulation sequence d of serial is carried out serial/parallel changing, obtain L group Parallel Sequence; For l group subcarrier, Parallel Sequence is expressed as m=1,2 ..., M; L=1,2 ..., L; β is spreading factor;

Step 3, employing chaos reference sequences x ^lrespectively by information bit spread to and be assigned on m subcarrier of l group;

Described chaos reference sequences x ^lproduced by 2 rank Chebyshev inequalities (CPF);

Wherein: 2 rank Chebyshev inequalities are:

$x_{j+1}=1-{2x}_j^2,(-1<x_j<1,\&NotEqual;\{0,\&PlusMinus;0.5\left\}\right)$

For l group, order represent chaos reference sequences;

Step 4, by Parallel Sequence through IFFT conversion and parallel/serial conversion after, be sent in wireless channel;

The signal acceptance method of OFDM-DCSK communication system is:

Step 5, receiving terminal be Received signal strength r from wireless channel, and after serial/parallel conversion and FFT conversion, obtains Parallel Sequence;

Step 6, decode to often organizing sequence respectively, the decode procedure often organizing subcarrier is identical, and for first group of subcarrier, its coding/decoding method is:

First, central subcarrier is stored in matrix P, and all the other M data-signal is stored in second matrix S; Provide respectively in matrix P and S formula below:

$P=(x_0^1+n_0^1,x_1^1+n_1^1,...,x_{\mathrm{\&beta;}-1}^1+n_{\mathrm{\&beta;}-1}^1)---\left(1\right)$

$S=\left(\begin{array}{ccc}{d}_1^1{x}_0^1+n_{\mathrm{1,0}}^1& ...& d_1^1{x}_{\mathrm{\&beta;}-1}^1+n_{1,\mathrm{\&beta;}-1}^1\\ .& .& .\\ .& .& .\\ .& .& .\\ d_M^1{x}_0^1+n_{M,0}^1& ...& d_M^1{x}_{\mathrm{\&beta;}-1}^1+n_{M,\mathrm{\&beta;}-1}^1\end{array}\right),---\left(2\right)$

Wherein: for being added to a jth sample of AWGN in reference signal, for being added to a jth sample of the AWGN in first group of m subcarrier;

After the β section time, all samples are all stored in an OFDM-DCSK frame, and decoding step is activated, and finally, M bit of transmission is decoded by the symbol parallel of compute matrix product;

Wherein: × be multiplication of matrices, ' transposition of representing matrix;

Step 7, decoded signal is carried out parallel/serial conversion, and carry out demodulation, obtain original information bits b, and export.

2. OFDM-DCSK communication system according to claim 1, is characterized in that the concrete grammar that M the bit sent described in step 6 is decoded by the symbol parallel of compute matrix product is:

Steps A, initial m=1;

Step B, according to formula:

$D_m^1={\mathrm{\&Sigma;}}_{j=0}^{\mathrm{\&beta;}-1}(d_j^1{x}_j^1+n_{m,j}^1)(x_j^1+n_j^1)$

Calculating observation signal and

Step C, by observation signal and compare with threshold value 0:

Complete the decoding to this group sequence;

Step D, judge whether m=M, if so, then terminate; If not, then execution step B is returned.