阅读说明：本技术 一种多用户正交频分复用差分混沌键控通信方法 (Multi-user orthogonal frequency division multiplexing differential chaos keying communication method ) 是由 任海鹏 赵晓辉 白超 李洁 于 2020-12-25 设计创作，主要内容包括：本发明公开了一种多用户正交频分复用差分混沌键控通信方法,步骤包括：1)设置通信系统参数；2)为P个用户分配索引值；3)每个用户利用索引值对应选择参考符号序列；4)生成各用户的混沌参考信号；5)为各用户的混沌参考信号分配子载波；6)构成该用户的信息承载信号；7)构建逆傅里叶变换输入矩阵；8)得到发送信号；9)对接收信号依次进行移除循环前缀、串并转换、傅里叶变换；10)进行最大信噪比点采样；11)采样序列重组；12)用户索引值恢复判决；13)选择参照矩阵对应行的元素序列作为新的混沌参考序列；14)用户传输信息数据解码。本发明的方法,使得混沌参考序列更加准确,进一步提升通信系统的误码率性能。(The invention discloses a multi-user orthogonal frequency division multiplexing differential chaos keying communication method, which comprises the following steps: 1) setting communication system parameters; 2) allocating index values for P users; 3) each user correspondingly selects a reference symbol sequence by using the index value; 4) generating chaotic reference signals of each user; 5) distributing sub-carriers for the chaotic reference signals of each user; 6) forming an information bearing signal for the user; 7) constructing an inverse Fourier transform input matrix; 8) obtaining a sending signal; 9) removing a cyclic prefix, performing serial-to-parallel conversion and performing Fourier transform on a received signal in sequence; 10) sampling the point with the maximum signal-to-noise ratio; 11) sample sequence recombination; 12) user index value recovery judgment; 13) selecting an element sequence of a row corresponding to the reference matrix as a new chaotic reference sequence; 14) and decoding the user transmission information data. The method of the invention ensures that the chaos reference sequence is more accurate, and further improves the error rate performance of the communication system.)

1. A multi-user orthogonal frequency division multiplexing differential chaos keying communication method is characterized by comprising the following steps:

step 1, setting relevant parameters of a communication system;

step 2, distributing index value I to P users of information to be sent_pPreparing binary bit information b to be transmitted for each user_i,pThe subscript i is 1,2, …, M, P is 1,2, …, and P indicates the ith bit of the data transmitted by the pth user in a frame;

step 3, each user correspondingly selects element sequences of different rows of the Hadamard matrix by using the index values as reference symbol sequences

Step 4, the reference symbol sequence corresponding to each user is used as the input of the chaotic forming filter to generate chaotic reference signals corresponding to each user;

step 5, copying the chaotic reference signals of all users, distributing subcarriers for the chaotic reference signals of all users, and distributing the chaotic reference signal X obtained in the step 4_p(t) repeating C times to obtainC, 1,2, 4, distributing C private subcarrier frequencies uniformly distributed in a used frequency band for each user to transmit corresponding chaotic reference signals;

step 6, multiplying the bit data of the information to be transmitted of each user by the chaotic reference signal of the user to form an information bearing signal of the user, adding the information bearing signals corresponding to the users to obtain a sending signal in a shared subcarrier, sampling each subcarrier signal according to a sampling frequency to obtain corresponding sampling points to form a partial row of an inverse Fourier transform input matrix, and preparing for inverse Fourier transform;

step 7, adding comb-shaped pilot frequency, filling zero, and constructing an inverse Fourier transform input matrix;

step 8, performing inverse Fourier transform on the inverse Fourier transform input matrix column by column, performing parallel-serial conversion on the output of the inverse Fourier transform input matrix, and adding a cyclic prefix to obtain a sending signal;

step 9, after receiving the sending signal, the receiving end sequentially removes the cyclic prefix, performs serial-to-parallel conversion and performs Fourier transform on the received signal, extracts the received user chaotic reference signal and the information bearing signal according to the preset subcarrier, averages the C times chaotic reference signal transmitted by the user, and performs matched filtering with the information bearing signal respectively;

step 10, sampling the maximum signal-to-noise ratio points of the filtered chaotic reference signal and the filtered information bearing signal to obtain maximum signal-to-noise ratio point sequences X 'and Y' respectively sampled by the chaotic reference signal and the information bearing signal;

step 11, sample sequence recombination, namely recombining a chaos reference signal sample sequence and an information bearing sample sequence of a user respectively;

step 12, user index value recovery judgment, wherein each row of the Hadamard matrix which is the same as the transmitting end is firstly subjected to maximum signal-to-noise ratio point sampling on the output signal of the matched filter through a forming filter and the matched filter respectively to obtain a new reference matrix; calculating the Euclidean distance between the reference sequence recombined by the user and each row of the reference matrix, and selecting the row with the minimum distance as the recovered user index value;

step 13, selecting the element sequence of the corresponding row of the reference matrix as a new chaotic reference sequence by using the recovered index value, namely, according to the estimated value of the index value obtained in step 12Selecting the row corresponding to the mapping reference matrix as a new chaotic reference sequenceSubstitution of the recombined chaotic reference sequence

Step 14, decoding the user transmission information data, and carrying the information bearing sequence Y in step 11^infAnd the chaos reference sequence obtained in step 13The transpose of the data is multiplied, the symbol decision is taken as the product result, and the transmission data is recovered to finish decoding.

2. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 1, wherein: in the step 1, the specific process is that the fundamental frequency f of the chaotic shaping filter is set_sSpread spectrum gain coefficient beta, sampling frequency f_cA gain coefficient n of chaotic sign_s＝f_c/f_sDefining the number P of users and the number M of binary information bits which can be sent by each user in a frame of transmission signal;

setting subcarrier parameters including total carrier number N and number N of shared information transmission subcarriers_mThe number of the reference signal extension sub-carriers C of each user and the number of the comb-shaped pilot frequency sub-carriers N_ctAnd the number No of guard interval subcarriers, and satisfy N ═ N_m+P*C+N_ct+N_o(ii) a Defining the length L of cyclic prefix, and setting the dimension N of Hadamard matrix_s＝β/n_sAnd generating a Hadamard matrix.

3. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 2, wherein: in the step 4, the specific process is thatThe chaos reference signals are respectively used as the input of the following chaos shaping filter to obtain the output chaos reference signals, as shown in formula (1):

wherein t is the time for generating a user chaotic reference signal, X_p(T) is the output of the chaotic shaping filter as the chaotic reference signal of the pth user, T_s＝1/f_sFor a symbol in a sequence of reference symbolsThe basis function ψ (t) is as shown in equation (2):

wherein f is_sFor the fundamental frequency of the chaotic shaping filter set in step 1, the parameter ω is 2 π f_s，η＝f_sln2。

4. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 3, wherein: in step 6, the specific process is that the information-bearing signal transmitted by the ith shared subcarrier carries the ith bit superposition information of all P users, and the information-bearing signal is as shown in the following formula (3):

wherein b is_i,pI-th binary data, i-1, 2, M, X, representing the p-th user transmission_p(t) is the chaotic reference signal of the p-th user,

transmitting signal Y for each subcarrier_i(t) according to the sampling frequency f_cSampling to obtain a sampling matrix of the information bearing signal:

wherein Y is_i(k)＝Y_i(kΔt)，Δt＝1/f_cIs the sampling time.

5. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 4, wherein: in the step 7, the specific process is to set N_ctEach subcarrier transmits a comb-shaped pilot signal consisting of bipolar symbols of (N)_ctX beta) matrix, and pilot frequency sub-carriers are uniformly inserted into the sub-carriers of the chaotic reference signal and the information carrying signal; the chaotic reference signal obtained in the step 5 is used forAccording to the sampling period delta t being 1/f_cSampling to obtain a chaotic reference signal sampling matrix, an information bearing signal sampling matrix Y obtained in the step 6 and a comb-shaped pilot signal matrix in the front of the step, and arranging the chaotic reference signal sampling matrix, the information bearing signal sampling matrix Y and the comb-shaped pilot signal matrix in parallel according to a preset sequence, wherein the rest N are₀Row complementary zero matrix U_oAnd obtaining a matrix with the size of (N multiplied by beta) as an inverse Fourier transform input matrix.

6. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 5, wherein: in step 8, the specific process is that the inverse fourier transform input matrix (N × β) obtained in step 7 is used as the input of inverse fourier transform, each column performs N-point IFFT operation to complete an OFDM symbol transform, β (column) IFFT operations are performed for a frame, and the IFFT outputs are parallel-to-serial converted to obtain a time domain signal s (t), which is represented by formula (4):

where k is a sampling point of a signal on one subcarrier, and f is a sampling point of a signal on one subcarrier_c,pThe sub-carrier frequency of the c reference expansion of the p user, f_iFor the ith information carrying signal subcarrier frequency, f_dAnd f_oThe carrier frequencies of the comb pilot and the zero padding matrix are respectively, d is 1,2, …, N_ct，o＝1,2,…,N_o(ii) a And then, copying L sampling points at the tail of the beta sampling points corresponding to each OFDM symbol, and adding the copied sampling points to the front end of the symbol to be used as cyclic prefixes, so as to obtain the sending signal.

7. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 6, whereinIs characterized in that: in step 9, the specific process is that the received signal r of the p-th user is_p(t) obtaining an (Nxbeta) Fourier transform output matrix by removing the cyclic prefix, performing serial-to-parallel conversion and Fourier transform, and then extracting the chaotic reference signal X 'and the information bearing signal Y' of the user according to preset subcarrier allocation, as shown in formula (5):

wherein the content of the first and second substances,k-th sampling point, Y ', representing the c-th copy of the received p-th user chaotic reference signal'_i,kA kth sampling point representing a received ith information-bearing signal; n is₁(k) And n₂(k) Respectively representing the noise of a channel during the transmission of the chaotic reference signal and the noise of the channel during the transmission of the information bearing signal;represents the equivalent multi-path fading channel impulse response transmitted by the c-th chaotic reference signal copy of the p-th user in the channel,representing the equivalent multipath fading channel impulse response transmitted by the information-bearing signal received by the p-th user in the ith subcarrier channel, the expression of the impulse responses of the two multipath fading channels is shown as the formula (6):

wherein the content of the first and second substances,and τ_l,p,cRespectively representing the attenuation coefficient and delay time of the ith path of the channel in which the chaotic reference signal is transmitted, L_p,cThe number of multipath of the c sub-carrier channel of the p user; in the same way as above, the first and second,and τ_l′,iRespectively representing the attenuation coefficient and delay time of the L' th path of the channel in which the information-bearing signal is transmitted, L_iAs to the number of multi-paths,

since the chaotic reference signal of each user is copied for C times, the received C chaotic reference signals are averaged to obtain an averaged chaotic reference signal of the userAs shown in the following formula (7):

then, the averaged chaotic reference signal and information bearing signal are subjected to matched filtering to obtain a chaotic reference signal X 'and an information bearing signal Y' which are subjected to matched filtering, and the output of the matched filtering is as shown in a formula (8):

wherein g (t) ═ ψ (-t) is the time inverse function of the basis function of the chaotic shaping filter, X ″_p,kThe k sampling point, Y' of the output signal of the filter after the chaos reference signal of the p user is averaged_i,kRepresenting the kth sample point of the output signal after the ith information-bearing signal has passed through the filter.

8. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 7, wherein: in the step 10, the specific process is that the chaos reference signal and the information-bearing signal are sampled respectively to obtain maximum snr point sequences X '″ and Y' ″, and the expression is as shown in formula (9):

wherein w' is 1,2_sThe number of sampling points is the maximum signal-to-noise ratio.

9. The multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 8, wherein: in the step 11, the specific process is to recombine the chaos reference signal sampling sequence and the information bearing sampling sequence of the user respectively, and the expression is shown as the formula (10):

10. the multi-user orthogonal frequency division multiplexing differential chaos keying communication method of claim 9, wherein: in the step 12, the specific process is to set a reference matrix obtained by sampling each row of the Hadamard matrix with the maximum snr point after CSF and MF asg_qIs the q-th row in the reference matrix; then calculating Euclidean distance between the recombined reference sequence and each row in the reference matrix G, and selecting the row with the minimum distance as the estimation of the user index valueValue ofThe expression is shown in formula (11):

wherein sum (·) is summation operation, and min {. is minimum value operation.

Technical Field

The invention belongs to the technical field of chaotic communication, and relates to a multi-user orthogonal frequency division multiplexing differential chaotic keying communication method.

Background

The chaotic signal is widely applied to communication due to the characteristics of wide frequency spectrum, noise-like noise, initial value sensitivity and the like, the chaotic communication is initially developed rapidly as a secret communication scheme, and the secret performance of the chaotic secret communication is proved to have no obvious advantages along with the research depth, so the research of the chaotic communication is transferred to the research of improving the communication performance by using chaos under an actual channel. Chaotic communication is not only successfully applied to fiber channels, but also a chaotic differential keying scheme, which is a classic spread spectrum communication scheme, forms a local area network communication standard, such as ieee802.15.6. However, due to the problems of low transmission efficiency, high error rate and the like of the chaotic differential keying scheme, the chaotic differential keying scheme based on the OFDM is provided, the transmission efficiency is improved, the error rate is lower, and a multiple access function is provided. In addition, the latest research results show that the chaos as a baseband signal receiving end can maximize the signal-to-noise ratio through a simple matched filter; meanwhile, the chaotic characteristic can also be used to solve an inter-symbol interference (ISI) problem in wireless communication.

Although chaos differential keying schemes based on OFDM have achieved good performance. But the system error rate is higher because the system introduces larger interference among users in the multiple access. Therefore, it is important to further obtain a lower error rate while reducing the inter-user interference in the multiple access.

Disclosure of Invention

The invention aims to provide a multi-user orthogonal frequency division multiplexing differential chaos keying communication method, which solves the problems of large multi-access interference and high error rate in the prior art.

The technical scheme adopted by the invention is that a multi-user orthogonal frequency division multiplexing differential chaos keying communication method is implemented according to the following steps:

step 1, setting relevant parameters of a communication system;

step 2, distributing index value I to P users of information to be sent_pPreparing binary bit information b to be transmitted for each user_i,pThe subscript i is 1,2, …, M, P is 1,2, …, and P indicates the ith bit of the data transmitted by the pth user in a frame;

step 3, each useThe user uses the index value to correspondingly select the element sequence of different rows of the Hadamard matrix as the reference symbol sequence

Step 4, the reference symbol sequence corresponding to each user is used as the input of the chaotic forming filter to generate chaotic reference signals corresponding to each user;

step 5, copying the chaotic reference signals of all users, distributing subcarriers for the chaotic reference signals of all users, and distributing the chaotic reference signal X obtained in the step 4_p(t) repeating C times to obtainC, 1,2, 4, distributing C private subcarrier frequencies uniformly distributed in a used frequency band for each user to transmit corresponding chaotic reference signals;

step 6, multiplying the bit data of the information to be transmitted of each user by the chaotic reference signal of the user to form an information bearing signal of the user, adding the information bearing signals corresponding to the users to obtain a sending signal in a shared subcarrier, sampling each subcarrier signal according to a sampling frequency to obtain corresponding sampling points to form a partial row of an inverse Fourier transform input matrix, and preparing for inverse Fourier transform;

step 7, adding comb-shaped pilot frequency, filling zero, and constructing an inverse Fourier transform input matrix;

step 8, performing inverse Fourier transform on the inverse Fourier transform input matrix column by column, performing parallel-serial conversion on the output of the inverse Fourier transform input matrix, and adding a cyclic prefix to obtain a sending signal;

step 9, after receiving the sending signal, the receiving end sequentially removes the cyclic prefix, performs serial-to-parallel conversion and performs Fourier transform on the received signal, extracts the received user chaotic reference signal and the information bearing signal according to the preset subcarrier, averages the C times chaotic reference signal transmitted by the user, and performs matched filtering with the information bearing signal respectively;

step 10, sampling the maximum signal-to-noise ratio points of the filtered chaotic reference signal and the filtered information bearing signal to obtain maximum signal-to-noise ratio point sequences X 'and Y' respectively sampled by the chaotic reference signal and the information bearing signal;

step 11, sample sequence recombination, namely recombining a chaos reference signal sample sequence and an information bearing sample sequence of a user respectively;

step 12, user index value recovery judgment, wherein each row of the Hadamard matrix which is the same as the transmitting end is firstly subjected to maximum signal-to-noise ratio point sampling on the output signal of the matched filter through a forming filter and the matched filter respectively to obtain a new reference matrix; calculating the Euclidean distance between the reference sequence recombined by the user and each row of the reference matrix, and selecting the row with the minimum distance as the recovered user index value;

step 13, selecting the element sequence of the corresponding row of the reference matrix as a new chaotic reference sequence by using the recovered index value, namely, according to the estimated value of the index value obtained in step 12Selecting the row corresponding to the mapping reference matrix as a new chaotic reference sequenceSubstitution of the recombined chaotic reference sequence

Step 14, decoding the user transmission information data, and carrying the information bearing sequence Y in step 11^infAnd the chaos reference sequence obtained in step 13The transpose of the data is multiplied, the symbol decision is taken as the product result, and the transmission data is recovered to finish decoding.

The beneficial effects of the invention are as follows:

1) the technology of the invention can reduce the multiple access interference. And each user at the transmitting end generates a chaotic reference signal by using row elements of the Hadamard matrix as a reference symbol sequence according to the index value, and the interference of other users to the current user is smaller when the users are distinguished due to the complete orthogonality among the rows of the Hadamard matrix. Since the order of the Hadamard matrix is an integral power of 2, the error rate will not be deteriorated with the increase of the number of users as long as the number of actual users is less than the maximum limited number of users in a certain spread spectrum range. Therefore, compared with the traditional OFDM differential keying scheme, the invention has smaller multiple access interference, thereby improving the system error rate performance.

2) The invention can obtain lower transmission error rate by utilizing the chaotic forming filter and the corresponding matched filter. The effect of maximizing the signal-to-noise ratio is achieved by using the corresponding matched filter at the receiving end, and the bit error rate performance is better due to the application of the point of maximizing the signal-to-noise ratio. The receiving end recovers the index value by using a maximum likelihood method, and then obtains an accurate reference sequence by using the index value, thereby further improving the error rate performance of the system.

Drawings

FIG. 1 is a block diagram of a transmitting end employed in the method of the present invention;

FIG. 2 is a block diagram of a receiving end employed by the method of the present invention;

FIG. 3 is a graph of the basis function of a chaotic shaping filter used in the method of the present invention;

FIG. 4 is a chaotic reference signal generated by a chaotic shaping filter according to the method of the present invention;

FIG. 5 is an information bearing signal to be transmitted in accordance with an embodiment of the method of the present invention;

FIG. 6 is a real part of a transmission signal according to an embodiment of the method of the present invention;

FIG. 7 illustrates an embodiment of the method of the present invention receiving an output signal of a chaotic reference signal through a matched filter;

FIG. 8 is a block diagram of a method embodiment of the present invention for receiving an information-bearing signal and outputting the signal through a matched filter;

FIG. 9 shows bit error rate simulation results of different methods for single users and 3 users under different spreading gains under Gaussian channels;

fig. 10 shows bit error rate simulation results of different methods for different spreading gains of single users and 3 users under a wireless channel;

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Referring to fig. 1 and fig. 2, which are block diagrams of a transmitting end and a receiving end of a communication system adopted by the method of the present invention, the method of the present invention is based on a chaos shaping filter and a Hadamard index modulation multi-user OFDM differential keying communication, and is specifically implemented according to the following steps:

step 1, setting relevant parameters of a communication system,

setting fundamental frequency f of chaotic shaping filter_sSpread spectrum gain coefficient beta, sampling frequency f_cA gain coefficient n of chaotic sign_s＝f_c/f_sDefining the number P of users and the number M of binary information bits which can be sent by each user in a frame of transmission signal;

setting subcarrier parameters including total carrier number N and number N of shared information transmission subcarriers_mThe number of the extended subcarriers C of each user reference signal, the number of the comb pilot subcarriers Nct and the number of the guard interval subcarriers No, and N is equal to N_m+P*C+N_ct+N_o(ii) a Defining the length L of cyclic prefix, and setting the dimension N of Hadamard matrix_s＝β/n_sGenerating a Hadamard matrix;

in the embodiment, the fundamental frequency f of the chaotic shaping filter is set_s2.5MHz, sampling frequency f_c40MHz, a chaotic sign gain coefficient n_sLet Hadamard matrix dimension N16_sWhen the spreading gain coefficient is 8, the spreading gain coefficient is n_s*N_s128, the number P of users is 5, and each user sends information M of one frame of transmission signal with 48 bits (binary number); subcarrier setting N128, Nm 48, C4, Nct 4, cyclic prefix length L4, the Hadamard matrix generated is as follows:

step 2, distributing P users of information to be sentIndex value I_pPreparing binary bit information b to be transmitted for each user_i,pThe subscript i is 1,2, …, M, P is 1,2, …, and P indicates the ith bit of the data transmitted by the pth user in a frame;

in the embodiment, it is assumed that 5 users of information to be transmitted are assigned index values, i.e. I₁＝1，I₂＝2，I₃＝3，I₄＝4，I₅Each subscriber transmits 48 binary bit information b, 5_i,pWherein i is 1,2, 48, and p is 1,2, 5.

Step 3, each user correspondingly selects element sequences of different rows of the Hadamard matrix by using the index values as reference symbol sequences

In the embodiment, 5-user scenes are selected, wherein the first 5 rows are selected as indexes in the selection sequence, and the 1 st user selects the first 5 rows as indexes according to the index value I₁The first row of the Hadamard matrix is selected as the reference symbol sequence 1, i.e.w＝1,2,...,N_sRepresents a vector subscript; and so on to obtain the reference symbol sequences of other 4 users

Step 4, the reference symbol sequence corresponding to each user is used as the input of the chaotic shaping filter to generate the chaotic reference signal corresponding to each user,

will be provided withThe output Chaotic reference signals are respectively obtained as the inputs of a Chaos Shaping Filter (CSF) as follows, and are shown in formula (1):

wherein t is the time for generating a user chaotic reference signal, X_p(T) is the output of the chaotic shaping filter as the chaotic reference signal of the pth user, T_s＝1/f_sFor the duration of one symbol in the reference symbol sequence, the basis function ψ (t) is as shown in equation (2):

wherein f is_sFor the fundamental frequency of the chaotic shaping filter set in step 1, the parameter ω is 2 π f_s，η＝f_s ln2；

In the embodiment, the sampling frequency f is set in step 1_c40MHz, chaotic signal fundamental frequency f_s2.5MHz, a chaotic sign gain coefficient n_s16, the corresponding sampling time t is 0,1/f_c,2/f_c…, fig. 3 is a plot of the basis functions of the corresponding chaotic shaping filter. The chaos shaping filter realizes the convolution operation of the digital signal and the primary function psi (t), and the reference symbol sequence of each user in step 3As an input of the chaotic shaping filter, the chaotic reference signal of the 3 rd user in the embodiment is shown in FIG. 4, wherein the solid line is the generated chaotic reference signal X₃(t) dashed lines are corresponding reference symbol sequencesIn addition, due to the fundamental frequency f_s2.5MHz, available X₃(t) duration t ∈ [0,3.2 × 10 ∈ ]^-6)s。

Step 5, copying the chaotic reference signals of all users, distributing subcarriers for the chaotic reference signals of all users, and distributing the chaotic reference signal X obtained in the step 4_p(t) repeating C times to obtainc is 1,2, 4, eachC private subcarrier frequencies are uniformly distributed in a use frequency band by each user to send corresponding chaotic reference signals;

in an embodiment, C is 4, that is, the chaotic reference signal of each user obtained in step 4 is repeated 4 times, for example, the chaotic reference signal X of the 3 rd user₃(t) repeating the reaction 4 times to obtainThe 4 private subcarriers of the user are evenly distributed over the entire available spectrum to cope with frequency selective fading in the channel. In 5 user scenarios, 20 private subcarriers are used together to transmit the chaotic reference signal. The total carrier number is 128, and the 5-user private carrier range is set to ([31: 35)],[49:53],[67:71],[85:89])。

Step 6, multiplying the bit data of the information to be transmitted of each user by the user chaotic reference signal to form an information bearing signal of the user, adding the information bearing signals corresponding to the users to obtain a sending signal in a shared subcarrier, sampling each subcarrier signal according to a sampling frequency to obtain corresponding sampling points to form a part of rows of an inverse Fourier transform input matrix to prepare for inverse Fourier transform,

the information-bearing signal transmitted by the ith shared subcarrier carries the ith bit superposition information of all P users, and the information-bearing signal is shown in the following formula (3):

wherein b is_i,pI-th binary data, i-1, 2, M, X, representing the p-th user transmission_p(t) is the chaotic reference signal of the p-th user,

transmitting signal Y for each subcarrier_i(t) according to the sampling frequency f_cSampling to obtain a sampling matrix of the information bearing signal:

wherein Y is_i(k)＝Y_i(kΔt)，Δt＝1/f_cIs the sampling time;

in an embodiment, the 3 rd information carrying signalIs shown in fig. 5, in which the sampling points are marked with crosses, during which time the time is equal to 1/f in terms of Δ t_c＝4*10^-7A second sample may result in 128 samples. And drawing a graph and obtaining sampling points for other carrier transmission signals. In addition, 48 shared subcarriers are set to be allocated within 128 subcarriers in the range of ([36: 47)],[54:65],[72:83],[90:101])。

Step 7, adding comb-shaped pilot frequency, filling zero, constructing an inverse Fourier transform input matrix,

setting N_ctEach subcarrier transmits a comb-shaped pilot signal consisting of bipolar symbols of (N)_ctX beta) matrix, and pilot frequency sub-carriers are uniformly inserted into the sub-carriers of the chaotic reference signal and the information carrying signal; the chaotic reference signal obtained in the step 5 is used forAccording to the sampling period delta t being 1/f_cSampling to obtain a chaotic reference signal sampling matrix, an information bearing signal sampling matrix Y obtained in the step 6 and a comb-shaped pilot signal matrix in the front of the step, and arranging the chaotic reference signal sampling matrix, the information bearing signal sampling matrix Y and the comb-shaped pilot signal matrix in parallel according to a preset sequence, wherein the rest N are₀Row complementary zero matrix U_oObtaining a matrix with the size of (Nxbeta) as an inverse Fourier transform input matrix;

in the examples, N_ct4, the comb pilot consists of [1,1, -1,1]^TSpreading 128 times results in a (4 × 128) comb pilot signal matrix. And arranging the obtained reference signal sampling (20 × 128) matrix, the information bearing signal sampling (48 × 128) matrix and the comb-shaped pilot signal (4 × 128) matrix in parallel according to a preset sequence, and then complementing (56 × 128) zero matrixes to obtain (128 × 128) inverse Fourier transform input matrixes. In the step 5 and step 6 embodiments are givenChaotic reference signal and information bearing signal subcarrier range, comb pilot subcarrier range is ([30,48,66, 84)]) The remaining two sides of the subcarrier range ([1:31 ]],[102:128]) Is a guard interval.

Step 8, inverse Fourier transform is carried out on the inverse Fourier transform input matrix column by column, the output of the inverse Fourier transform input matrix is added with cyclic prefix after parallel-serial conversion to obtain a sending signal,

step 7, obtaining an inverse fourier transform input matrix of (N × β) as an input of inverse fourier transform, performing IFFT operation on N points in each column to complete an OFDM symbol transform, performing IFFT operation on a frame for β times (columns), and performing parallel-to-serial conversion on IFFT output to obtain a time domain signal s (t), which is represented by formula (4):

where k is a sampling point of a signal on one subcarrier, and f is a sampling point of a signal on one subcarrier_c,pThe sub-carrier frequency of the c reference expansion of the p user, f_iFor the ith information carrying signal subcarrier frequency, f_dAnd f_oThe carrier frequencies of the comb pilot and the zero padding matrix are respectively, d is 1,2, …, N_ct，o＝1,2,…,N_o(ii) a Then, copying L sampling points at the tail of the beta sampling points corresponding to each OFDM symbol, and adding the copied sampling points to the front end of the symbol to be used as cyclic prefixes, so as to obtain a sending signal;

in an embodiment, the inverse fourier transform is input as a (128 × 128) matrix, and the output matrix is parallel-to-serial converted to obtain a time duration of (128 × 128) T_cT, T_c＝1/f_cFor the duration of one sample, then L-4 samples (corresponding to 4T) at the end of each OFDM symbol_cDuration) is added at the front of the symbol, resulting in a duration of (128 x (128+4)) T_cThe transmission signal of (1). The center frequency is set to be 1MHz in the formula (4), f_c,p、f_i、f_d、f_oCorresponding to the subcarrier ranges in the embodiments of step 5, step 6 and step 7, respectively. The real part of the corresponding time domain signal s (t) is shown in FIG. 6。

Step 9, after receiving the sending signal, the receiving end sequentially removes the cyclic prefix, performs serial-to-parallel conversion and performs Fourier transform on the received signal, extracts the received user chaotic reference signal and the information bearing signal according to the preset subcarrier, averages the C times chaotic reference signal transmitted by the user, and performs matched filtering with the information bearing signal respectively;

i.e. the received signal r of the p-th user_p(t) obtaining an (Nxbeta) Fourier transform output matrix by removing the cyclic prefix, performing serial-to-parallel conversion and Fourier transform, and then extracting the chaotic reference signal X 'and the information bearing signal Y' of the user according to preset subcarrier allocation, as shown in formula (5):

wherein the content of the first and second substances,k-th sampling point, Y ', representing the c-th copy of the received p-th user chaotic reference signal'_i,kA kth sampling point representing a received ith information-bearing signal; n is₁(k) And n₂(k) Respectively representing the noise of a channel during the transmission of the chaotic reference signal and the noise of the channel during the transmission of the information bearing signal; h_k,p,fcRepresents the equivalent multi-path fading channel impulse response transmitted by the c-th chaotic reference signal copy of the p-th user in the channel,representing the equivalent multipath fading channel impulse response transmitted by the information-bearing signal received by the p-th user in the ith subcarrier channel, the expression of the impulse responses of the two multipath fading channels is shown as the formula (6):

wherein the content of the first and second substances,and τ_l,p,cRespectively representing the attenuation coefficient and delay time of the ith path of the channel in which the chaotic reference signal is transmitted, L_p,cThe number of multipath of the c sub-carrier channel of the p user; in the same way as above, the first and second,and τ_l′,iRespectively representing the attenuation coefficient and delay time of the L' th path of the channel in which the information-bearing signal is transmitted, L_iAs to the number of multi-paths,

since the chaotic reference signal of each user is copied for C times, the received C chaotic reference signals are averaged to obtain an averaged chaotic reference signal of the userAs shown in the following formula (7):

then, the averaged chaotic reference signal and information bearing signal are subjected to matched filtering to obtain a chaotic reference signal X 'and an information bearing signal Y' which are subjected to matched filtering, and the output of the matched filtering is as shown in a formula (8):

wherein g (t) ═ ψ (-t) is the time inverse function of the basis function of the chaotic shaping filter, X ″_p,kThe k sampling point, Y' of the output signal of the filter after the chaos reference signal of the p user is averaged_i,kA kth sampling point representing an output signal of the ith information-bearing signal after passing through the filter;

in the embodiment, in order to clearly show the signal variation law, an ideal channel model is considered, namely n₁(t)＝n₂(t) 0 and H_k,p,fc＝H_k,p,fi1. The matched filter realizes the convolution operation of the time inverse of the received signal and the basis function, and the 3 rd user filtered chaotic reference signal and the i-3 th bit information bearing signal X ″₃(t) and Y ″)₃(t) are shown in FIGS. 7 and 8, respectively.

Step 10, maximum signal-to-noise ratio point sampling is carried out on the filtered chaotic reference signal and the filtered information bearing signal, so as to obtain maximum signal-to-noise ratio point sequences X 'and Y' respectively sampled by the chaotic reference signal and the information bearing signal, wherein an expression is shown as a formula (9):

wherein w' is 1,2_sSampling points with the maximum signal-to-noise ratio;

in the examples, β 128, N_sThe filtered signal obtained in step 9 is sampled according to the above formula (9), and the corresponding sampling sequence and sampling value are shown in table 1 below, and the star marks in fig. 7 and fig. 8.

Table 1, sample sequences and sample values of the 3 rd user chaotic reference signal and the i ═ 3 th information carrying signal after filtering in the embodiment

Step 11, sample sequence recombination, namely recombining the chaos reference signal sample sequence and the information bearing sample sequence of the user respectively, wherein the expression is shown as the formula (10):

in the embodiment, the sampling sequences obtained in step 10 are respectively recombined according to the above formula (10) to obtain the chaos reference sequence and the information bearing sequence of the 3 rd user, and the expression is as follows:

step 12, user index value recovery judgment, wherein each row of the Hadamard matrix which is the same as the transmitting end is firstly subjected to maximum signal-to-noise ratio point sampling on the output signal of the matched filter through a forming filter and the matched filter respectively to obtain a new reference matrix; then calculating Euclidean distance between the reference sequence recombined by the user and each row of the reference matrix, selecting the row with the minimum distance as the recovered user index value,

let the reference matrix obtained by sampling each row of the Hadamard matrix with the maximum SNR point after CSF and MF beg_qIs the q-th row in the reference matrix; then calculating Euclidean distance between the recombined reference sequence and each row in the reference matrix G, and selecting the row with the minimum distance as the estimated value of the user index valueThe expression is shown in formula (11):

wherein sum (·) is summation operation, and min {. } is minimum value calculation;

in an embodiment, the expression of the reference matrix is:

subjecting to step 11And the reference matrix is substituted into the formula (11) to obtain

Step 13, selecting the element sequence of the corresponding row of the reference matrix as a new chaotic reference sequence by using the recovered index value, namely, according to the estimated value of the index value obtained in step 12Selecting the row corresponding to the mapping reference matrix as a new chaotic reference sequenceSubstitution of the recombined chaotic reference sequence

In the embodiment, the index value estimated value calculated by the 3 rd user at the receiving end isThus, the 3 rd row of the mapping reference matrix G is selected as a new chaotic reference sequence, i.e.And so on to analogize the chaotic reference sequences of the other four users.

Step 14, decoding the user transmission information data, and carrying the information bearing sequence Y in step 11^infAnd the chaos reference sequence obtained in step 13The transpose multiplication, the symbol decision is taken as the result of the multiplication, the transmission data is recovered to finish the decoding,

estimated value of M binary data recovered by p-th userAs shown in equation (12):

wherein (.)^TRepresenting matrix transposition, sgn { } representing symbol taking operation, and finally obtainingThe matrix is used for completing the decoding process for M binary data transmitted by a frame of the pth user;

in the embodiment, the example of decoding the transmission bit data of the 3 rd user and the information carrying sequence Y obtained in step 11^infAnd the chaos reference sequence obtained in step 13Belt (12), the calculation results are as follows:

binary data estimation value transmitted by other usersAnd by parity of reasoning, finishing the whole decoding process to obtain the final product.

Simulation verification:

1) error rate in single path channel.

The simulation adopts a gaussian channel model, the error rate performance of different schemes under the same spreading gain and the same user access number is tested, and the simulation result is shown in fig. 9. The simulation is compared with a chaos keying modulation scheme based on multi-user OFDM. The spread spectrum gain of all schemes is set to be beta-64 and 256, the number of users is single user and 3 users, and the sampling frequency f_c40MHz, wherein the scheme has a chaotic signal fundamental frequency f_s2.5MHz, then corresponds to n_s16. Setting M to 48 indicates that 48 binary bits of information are transmitted per user per frame. In fig. 9, the abscissa represents the signal-to-noise ratio and the ordinate represents the bit error rate. The dash-dot line and the dot-dash-dot line in the figure are error rate curves of the comparison scheme in a single-user scene and a 3-user scene beta of 64 respectively, and the left triangular dot-dot line and the right triangular dot-The dotted lines are error rate curves of the comparison scheme in the single-user and 3-user scenarios β ═ 256, the dotted lines and the circular dotted lines are error rate curves of the proposed scheme in the single-user and 3-user scenarios β ═ 64, respectively, and the solid lines and the circular straight lines are error rate curves of the proposed scheme in the single-user and 3-user scenarios β ═ 256, respectively. As can be seen from the simulation result of fig. 9, the method of the present invention has a lower error rate at the same spreading gain and the same number of user accesses compared to the comparison scheme (the chaos keying modulation scheme based on multi-user OFDM). Meanwhile, different from the comparison scheme, the method provided by the invention has the advantage that the information error rate is basically kept constant along with the increase of the user number M on the premise of a single-path channel and fixed spread spectrum gain.

2) Error rate under wireless channel.

Under a wireless channel, the bit error rate performance under the same spreading gain and the same user access number is shown in fig. 10, all communication parameter settings are consistent with the simulation under the gaussian channel, and the meaning of each curve representation in fig. 10 is consistent with that in fig. 9. The average power gain of the three paths in the simulation is E₁＝0.6、E₂＝0.3、E₃0.1, each corresponding delay time τ₁0 second,. tau₂0.0000009 seconds,. tau₂0.000001 sec. It can be seen that the method of the present invention always has better error code performance under the same spread spectrum gain and user number.

In summary, the method of the present invention uses the chaotic shaping filter to generate the chaotic reference signal, and uses the matched filter to reduce the interference effect, and the chaotic signal realizes the modulation of the user index Hadamard matrix symbol, so that the communication system has multi-user capability, and the multiple access interference is greatly reduced. The receiving end reduces the influence of environmental noise by using the corresponding matched filter, and simultaneously, the chaotic reference sequence is more accurate by using the method of calculating the Euclidean distance and mapping, thereby further improving the error rate performance of the communication system.