OFDM-DCSK modulation and demodulation method and system based on chaos masking and diffusion scrambling encryption

Abstract

The invention relates to an OFDM-DCSK modulation and demodulation method and system based on chaos masking and diffusion scrambling encryption, and belongs to the technical field of communication. The method comprises the following steps: at a sending end, information bits to be transmitted are subjected to polarity modulation and serial-parallel conversion and then are subjected to diffusion and scrambling encryption processing with a pre-generated chaos reference sequence, reference signals are hidden in information carriers in a diagonal mode and then mapped to orthogonal subcarriers, and time domain signals are formed through inverse fast Fourier transform and are sent. After a receiving end receives a signal, serial-to-parallel conversion, fast Fourier transform, inverse scrambling, inverse diffusion, reference signal stripping, singular value decomposition and reconstruction and chaotic correlation detection are carried out in sequence, and finally information bit recovery is realized. According to the invention, the confidentiality and the anti-interference capability of the system can be effectively improved, the bit error rate is reduced, the spectrum utilization efficiency is improved, and the problems that the reference signal is easy to eavesdrop and the data rate is reduced in the prior art are avoided.

Description

Technical Field

[0001] The present invention relates to an OFDM-DCSK (Orthogonal Frequency Division Multiplexing-Differential Chaos Shift Keying, OFDM-DCSK) modulation and demodulation method and system based on chaos masking and diffusion scrambling encryption, belonging to the technical field of communications. Background Art

[0002] With the continuous advancement of chaos theory, chaotic digital modulation technology based on broadband non-periodic chaotic signals has emerged. Replacing traditional sinusoidal carriers with chaotic signals not only inherits the advantages of anti-interference and anti-multipath fading in spread spectrum communications, but also has the characteristics of simple circuit structure, excellent autocorrelation performance, high sensitivity to initial values, low probability of intercept, enhanced communication security, reduced hardware cost, and good multi-user discrimination capabilities. Therefore, it has become an important research direction in the fields of nonlinear science and information science. Differential Chaos Shift Keying (DCSK), as a typical chaotic modulation method, uses continuous time slots to transmit the reference signal and the chaotic carrier carrying information respectively, and constructs independent channels through time division multiplexing, thus avoiding the complex chaotic synchronization process. However, the DCSK system requires the introduction of a delay device, which leads to a decrease in data rate. At the same time, broadband delay lines are difficult to implement using standard CMOS processes, and the system is not adaptable to multipath environments. In addition, due to its use of a reference and information time division (TR) transmission mechanism, the overall spectrum utilization is low, further limiting its scope of application.

[0003] To improve spectrum efficiency and reduce the receiver's reliance on broadband delay lines, the OFDM-DCSK modulation and demodulation method achieves data separation in the frequency domain by transmitting the reference signal and information carrier signal in parallel on multiple orthogonal subcarriers, thus avoiding the need for time delay components in traditional DCSK. While OFDM-DCSK effectively improves spectrum efficiency and hardware implementation complexity, the DCSK scheme based on orthogonal frequency division multiplexing still fails to effectively mask the reference signal, posing potential security risks. Furthermore, the transmitter's processing is simple and fails to fully utilize the characteristics of chaotic systems to enhance data encryption. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel OFDM-DCSK modulation and demodulation method and system based on reference signal chaos masking and diffusion scrambling encryption, aiming to solve the technical problems in the prior art that the reference signal is easily eavesdropped and the system confidentiality is insufficient, while improving the overall communication reliability and anti-interference performance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a novel OFDM-DCSK modulation and demodulation method based on chaotic masking of reference signals and diffusion scrambling encryption. This method employs a two-end communication structure in which the transmitter and receiver work together. This method performs chaotic encryption on the signal to be transmitted within a symbol period and implements diffusion scrambling encryption to enhance system security. Specifically, the method comprises the following steps:

[0006] Step 1: Polarity modulation and serial / parallel conversion are performed on the signal to be transmitted to form multiple parallel polarity symbol streams;

[0007] Step 2: Generate a discrete chaotic sequence as a reference sequence based on a preset chaotic map, and multiply it element-by-element with the multiple parallel polarity symbol streams to obtain a multi-channel modulation information sequence;

[0008] Step 3: Embed the reference sequence into the multi-channel modulated information sequence to achieve chaotic masking, and then perform chaotic diffusion and scrambling operations on the chaotically masked modulated information sequence in sequence to obtain the encrypted multi-channel diffusion scrambled information sequence;

[0009] Step 4: The encrypted multi-path diffusion scrambled information sequence is mapped to several orthogonal subcarriers. After frequency domain to time domain conversion via inverse fast Fourier transform, it is synthesized into a serial signal and transmitted to the communication channel to complete signal modulation.

[0010] Step 5: After receiving the serial signal from the communication channel, it is restored to multiple parallel subcarrier signals, and the time domain parallel subcarrier signals are restored to the frequency domain representation through fast Fourier transform to obtain the frequency domain received signal;

[0011] Step 6: Perform inverse scrambling and inverse chaos diffusion operations on the frequency domain received signal in sequence to restore the signal structure before encryption. The restored signal is extracted and restored based on the known reference sequence to obtain the multi-channel modulation information sequence.

[0012] Step 7: Perform singular value decomposition on the recovered multi-channel modulation information sequence, perform correlation detection based on the singular value decomposition result, perform hard decision according to the result of the correlation detection, and realize signal demodulation based on the result of the hard decision.

[0013] The step 1 is specifically as follows:

[0014] Step 1.1: Polarity modulate the input N serial information bits, and output a {1,−1} symbol sequence, where 0 is mapped to +1 and 1 is mapped to −1, resulting in N serial polarity modulated bits.

[0015] Step 1.2: Convert the serial N polar modulation bits into N parallel polar symbol data streams in parallel.

[0016] The step 3 is specifically as follows:

[0017] Step 3.1: Embed the reference sequence diagonally into the N modulation information sequences to achieve chaotic masking and ensure that the reference sequence is not exposed, thereby obtaining N modulation information sequences containing the reference sequence.

[0018] Step 3.2: Perform a chaotic diffusion operation on the N modulated information sequences including the reference sequence;

[0019] Step 3.3: Perform a scrambling operation on the modulated information sequence after the chaotic diffusion operation based on the chaotic key matrix to complete spatial disturbance and obtain N encrypted multi-path diffusion scrambled information sequences.

[0020] The step 3.2 is specifically as follows:

[0021] A chaotic key sequence with the same dimension as the N modulation information sequences containing the reference sequence is obtained through chaotic mapping ;

[0022] Select the last key element of the chaotic key sequence as the initial diffusion value, and modulate the N information sequences containing the reference sequence. For each element in , the chaotic diffusion operation is completed recursively as follows:

[0023]

[0024] in, Indicates the first elements, represents the value after diffusion, Indicates the value of the previous diffusion, the initial diffusion value is , Indicates the Chaotic key sequence value;

[0025] The chaotic diffusion values are rearranged according to the size of the N modulation information sequences containing the reference sequence to obtain the matrix ,in, Indicates that the matrix will be obtained according to The dimension is reshaped, Representation matrix dimension.

[0026] The step 3.3 is specifically as follows:

[0027] A chaotic key matrix with the same dimension as the modulated information sequence after the chaotic diffusion operation is obtained through chaotic mapping;

[0028] The elements of each row in the modulated information sequence after the chaotic diffusion operation are sorted in ascending order according to the odd rows corresponding to the chaotic key matrix, and the even rows are reversed in index order;

[0029] Each column element in the modulated information sequence after the chaotic diffusion operation is sorted in descending order according to the odd columns corresponding to the chaotic key matrix, and the even columns are reversed in index order to obtain N encrypted multi-path diffusion scrambled information sequences.

[0030] The step 4 is specifically as follows:

[0031] Step 4.1: Map the encrypted N multi-channel diffusion scrambled information sequences onto N pre-defined orthogonal subcarriers to form frequency domain subcarrier signals, where each orthogonal subcarrier carries a corresponding diffusion scrambled information sequence;

[0032] Step 4.2: All frequency-domain subcarrier signals are transformed into orthogonal time-domain subcarrier signals through inverse fast Fourier transform (IFFT). This ensures that the subcarrier signals are orthogonal to each other in the time domain and are not subject to inter-subcarrier interference. The N time-domain subcarrier signals are then combined into a serial signal and sent to the communication channel to complete the transmission.

[0033] The step 7 is specifically as follows:

[0034] Step 7.1: Perform singular value decomposition on the recovered multi-channel modulation information sequence, retain only the largest singular value and its corresponding singular vector, and reconstruct an approximate signal matrix with rank 1;

[0035] Step 7.2: The first row of the reconstructed approximate signal matrix is used as the reference subcarrier, and the remaining rows are used as information subcarriers. Based on the reference subcarrier, correlation detection is performed on all information subcarriers one by one.

[0036] Step 7.3: Make a hard decision based on the positive or negative value of the correlation detection result and output a polarity symbol stream;

[0037] Step 7.4: Restore the polar symbol stream to a serial stream and convert it back to the original information bits to complete demodulation.

[0038] To achieve the above objectives, the present application also provides an OFDM-DCSK modulation and demodulation system based on chaotic masking and diffusion scrambling encryption, which is used to generate a preset number of carrier signals within a symbol period and embed the modulated polar modulation symbols and reference signals therein to achieve covert transmission and efficient demodulation. The system includes a transmitting modulator and a receiving demodulator. The transmitting modulator performs chaotic encryption on the polar symbol sequence and maps it to the subcarriers. The receiving demodulator is used to recover the information bit stream from the received signal. The system specifically includes:

[0039] Transmitter modulator: used to modulate the signal to be transmitted;

[0040] Receiver demodulator: used to receive the modulated signal and demodulate it.

[0041] The transmitting end modulator specifically includes:

[0042] Polarity converter: used to perform polarity modulation on the input serial information bit stream, mapping bit 0 to +1 and bit 1 to -1, generating a polarity symbol;

[0043] Serial-to-parallel converter: used to parallelize the serial polar symbol stream into N polar modulation symbol streams;

[0044] Chaotic signal generator: used to generate a discrete chaotic signal sequence within a symbol period based on a preset chaotic map;

[0045] Chaotic masking module: used to disperse and embed the reference chaotic sequence into the N-channel polar modulation symbol stream according to the diagonal insertion rule to form a masked information sequence;

[0046] Chaotic encryption module: includes a diffusion module and a scrambling module. The diffusion module is used to expand the masked information sequence element by element, using the key value to accumulate the expanded data element by element, so that each symbol is simultaneously affected by the current data, the diffusion history and the key sequence, enhancing the expansion correlation and unpredictability between data. The scrambling module is used to scramble the rows and columns according to the chaotic key matrix to generate an encrypted information sequence, thereby breaking the predictability of the data arrangement;

[0047] Carrier multiplier: used to map the encrypted information sequence to the corresponding N subcarrier frequencies;

[0048] Inverse Fast Fourier Transformer: used to inversely transform the frequency domain subcarrier signal into an orthogonal time domain signal;

[0049] Parallel-to-serial converter: used to combine the parallel time domain signals output by each subcarrier into a serial signal and send it to the communication channel.

[0050] The receiving end demodulator specifically includes:

[0051] Serial-to-parallel converter: used to convert the received serial time domain signal into N parallel subcarriers;

[0052] Fast Fourier Transformer: used to transform the parallel subcarrier time domain signals into frequency domain subcarrier symbols;

[0053] Chaotic encryption decryption module: including descrambling module and de-diffusion module, which is used to perform inverse scrambling and inverse diffusion operations in sequence to restore the original subcarrier structure before encryption;

[0054] Chaos demasking module: used to remove the reference signal and information signal from the recovered subcarrier signal according to the diagonal insertion rule;

[0055] Singular value auxiliary module: used to perform singular value decomposition on the recovered matrix, retain the maximum singular value and its corresponding singular vector, and reconstruct an approximate matrix with rank 1 to suppress the influence of channel noise;

[0056] Correlator: used to extract the correlation detection value between the reference subcarrier and each information subcarrier;

[0057] Decision maker: used to perform hard decision based on the positive or negative correlation value and output the corresponding polarity bit;

[0058] Parallel-to-serial converter: used to combine polarity bits into a recovered information bit stream for serial output.

[0059] Compared with the existing traditional OFDM-DCSK method, the present invention has the following beneficial effects:

[0060] At the transmitting end, the present invention performs diagonal chaotic masking on the reference signal, distributing and hiding the reference sequence into each information carrier, effectively improving the concealment of the reference signal and significantly enhancing the system's anti-interception capability and communication confidentiality. At the same time, by introducing a chaotic diffusion and scrambling module, the masked information sequence is key-driven expanded and randomly rearranged, breaking the regularity of traditional data arrangement and improving the system's anti-interference performance and anti-attack capabilities. During the demodulation process, the present invention adopts a singular value auxiliary detection mechanism to extract only the main singular components of the receiving matrix for rank-1 reconstruction, effectively suppressing the interference of channel noise on the reference signal and information signal, and improving demodulation accuracy.

[0061] In summary, the present invention can improve the confidentiality and robustness of the system while reducing the bit error rate, improving spectrum utilization efficiency, and enhancing overall communication reliability, and has broad prospects for engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 Flow chart of the steps of the present invention;

[0063] Figure 2 Schematic diagram of the structure of the transmitter modulator of the present invention;

[0064] Figure 3 Schematic diagram of the structure of the receiving end demodulator of the present invention;

[0065] Figure 4 This is a comparison chart of the error performance between the present invention and the existing OFDM-DCSK method in an additive white Gaussian noise channel. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described examples are only part of the examples of the present invention, rather than all the embodiments.

[0067] Example 1: Figure 1-Figure 3 As shown, the present invention provides an OFDM-DCSK modulation and demodulation method and system based on chaotic masking and diffusion scrambling encryption, which is suitable for performing polarity modulation and chaotic encryption processing on the information bit stream within the symbol period and mapping it to multiple subcarriers for transmission. The receiving end realizes accurate recovery of the information bits through inverse diffusion, inverse scrambling, demasking and singular value auxiliary detection.

[0068] Based on an OFDM-DCSK modulation and demodulation method based on chaos masking and diffusion scrambling encryption provided by the present invention, a reference signal chaos masking and diffusion scrambling encryption modulation and demodulation of the signal to be transmitted within the symbol period are performed, including a transmitting end and a receiving end, the transmitting end is used to modulate the signal to be transmitted within the symbol period through a modulator, and the reference signal chaos masking and diffusion scrambling encryption modulation and demodulation are performed. Figure 1 , specifically including the following steps:

[0069] Step 1: Perform polarity modulation and serial / parallel conversion on the signal to be transmitted to form multiple parallel polarity symbol streams.

[0070] Step 1.1: For the N serial information bits to be transmitted , polarity modulation is performed, bit 0 is mapped to +1, bit 1 is mapped to -1, and N polarity modulation bits are obtained. ;

[0071] Step 1.2: Convert the serial N polar modulation bits into N parallel polar symbol data streams. .

[0072] Step 2: Generate a discrete chaotic sequence as a reference sequence based on a preset chaotic map, and multiply it element-by-element with the multiple parallel polarity symbol streams to obtain a multi-channel modulation information sequence.

[0073] Step 2.1: Generate a discrete chaotic sequence of length β based on the pre-selected chaotic map , using it as a reference sequence for subsequent reference signal and encryption operations;

[0074] Step 2.2: Generate each polar modulation bit The generated reference sequence Perform element-by-element multiplication to generate N modulation information sequences :

[0075]

[0076] Step 3: Embed the reference sequence into the multi-channel modulation information sequence to achieve chaotic masking, and then perform chaotic diffusion and scrambling operations on the chaotically masked modulation information sequence in sequence to obtain the encrypted multi-channel diffusion scrambled information sequence.

[0077] Step 3.1: Embed the reference sequence diagonally into the N modulation information sequences to achieve chaotic masking and ensure that the reference sequence is not exposed. The N modulation information sequences containing the reference sequence are obtained as follows:

[0078]

[0079] in, It represents the modulation information sequence after the chaotic masking of the reference sequence is performed, that is, the reference sequence is replaced in sequence at the specified position of N information modulation sequences, and a part of the reference signal is embedded in each sequence;

[0080] Step 3.2: Perform a chaotic diffusion operation on the N modulated information sequences including the reference sequence;

[0081] A chaotic key sequence with the same dimension as the N modulation information sequences containing the reference sequence is obtained through chaotic mapping ;

[0082] Select the last key element of the chaotic key sequence as the initial diffusion value, and modulate the N information sequences containing the reference sequence. For each element in , the chaotic diffusion operation is completed recursively as follows:

[0083]

[0084] in, Indicates the first elements, represents the value after diffusion, Indicates the value of the previous diffusion, the initial diffusion value is , Indicates the Chaotic key sequence value;

[0085] The chaotic diffusion values are rearranged according to the size of the N modulation information sequences containing the reference sequence to obtain the matrix ,in, Indicates that the matrix will be obtained according to The dimension is reshaped, Representation matrix dimension.

[0086] Step 3.3: Perform a scrambling operation on the modulated information sequence after the chaotic diffusion operation based on the chaotic key matrix to complete spatial disturbance and obtain N encrypted multi-path diffusion scrambled information sequences.

[0087] A chaotic key matrix with the same dimension as the modulated information sequence after the chaotic diffusion operation is obtained through chaotic mapping ;

[0088] The elements of each row in the modulated information sequence after the chaotic diffusion operation are sorted in ascending order according to the odd rows corresponding to the chaotic key matrix, and the even rows are reversed in index order;

[0089] After the chaotic diffusion operation, the elements of each column of the modulated information sequence are sorted in descending order according to the odd columns corresponding to the chaotic key matrix, and the even columns are reversed in index order to obtain the encrypted N multi-way diffusion scrambled information sequences. .

[0090] Step 4: Map the encrypted multi-path diffusion scrambled information sequence onto several orthogonal subcarriers. After frequency domain to time domain conversion via inverse fast Fourier transform, synthesize the signals into a serial signal and transmit them to the communication channel to complete signal modulation.

[0091] Step 4.1: Map the encrypted N multi-channel diffusion scrambled information sequences onto N pre-defined orthogonal subcarriers to form frequency domain subcarrier signals, where each orthogonal subcarrier carries a corresponding diffusion scrambled information sequence;

[0092] Specifically, the obtained diffusion scrambled information sequence Divided into Information sequence , respectively mapped to Subcarrier , get the corresponding N subcarrier symbols , prepare for frequency domain modulation;

[0093] Step 4.2: All frequency-domain subcarrier signals are transformed into orthogonal time-domain subcarrier signals through inverse fast Fourier transform (IFFT). This ensures that the subcarrier signals are orthogonal to each other in the time domain and are not subject to inter-subcarrier interference. The N time-domain subcarrier signals are then combined into a serial signal and sent to the communication channel to complete the transmission.

[0094] Specifically, the modulated N subcarrier symbols Perform inverse fast Fourier transform to obtain the time domain signal :

[0095]

[0096] Ensure that the subcarriers are orthogonal in the time domain and do not interfere with each other.

[0097] Furthermore, the N parallel subcarrier time domain signals Merge into one serial transmission signal , and the transmission is completed through the Gaussian white noise channel.

[0098] Step 5: After receiving the serial signal from the communication channel, it is restored to multiple parallel subcarrier signals, and the time domain parallel subcarrier signals are restored to frequency domain representation through fast Fourier transform to obtain the frequency domain received signal.

[0099] Step 5.1: Receive the sent signal After that, it is converted back into N parallel subcarrier signals;

[0100] Step 5.2: Fast Fourier transform the N parallel subcarrier signals back to the frequency domain to recover the subcarrier components. :

[0101]

[0102] Step 6: Perform inverse scrambling and inverse chaos diffusion operations on the frequency domain received signal in sequence to restore the signal structure before encryption. The restored signal is extracted and restored to the multi-channel modulation information sequence based on the known reference sequence.

[0103] Step 6.1: The obtained N-channel subcarrier signals are passed through the descrambling module to restore the order of each information subcarrier according to the inverse scrambling rule, and then passed through the despreading module to remove the diffusion process and restore the subcarrier data matrix before chaotic encryption. ;

[0104] Step 6.2: Subcarrier data matrix before chaotic encryption After the chaos demasking module, based on the known chaotic reference sequence , according to the diagonal embedding rule, the despread subcarrier signal Perform the demasking operation to strip out the reference signal and information signal, and the received signal matrix is :

[0105]

[0106] in represents the original polar modulation bit, represents the reference sequence, and represent the channel noise added to the information modulation sequence and the reference sequence respectively.

[0107] Step 7: Perform singular value decomposition on the recovered multi-channel modulation information sequence, perform correlation detection based on the singular value decomposition result, perform hard decision according to the result of the correlation detection, and realize signal demodulation based on the result of the hard decision.

[0108] Step 7.1: Perform singular value decomposition on the recovered multi-channel modulation information sequence, retain only the largest singular value and its corresponding singular vector, and reconstruct an approximate signal matrix with rank 1;

[0109] Specifically, for the received signal matrix Perform singular value decomposition (SVD):

[0110]

[0111] in, represents the left singular matrix of the received signal matrix, is the singular value matrix of the received signal matrix, Represents the right singular matrix of the received signal matrix, and then arranges it in descending order according to the decomposed singular values, retaining only the largest singular value and its corresponding singular vector, and performs rank 1 approximate reconstruction:

[0112]

[0113] in, Represents a signal matrix of rank 1 reconstructed by the maximum singular value and the corresponding left and right singular vectors, represents the largest singular value in the received signal matrix, and are the left and right singular value vectors corresponding to the maximum singular value, respectively, to combat noise interference and retain the main signal components. ,in represents the reference signal, Indicates the modulated A chaotic sequence;

[0114] Step 7.2: The first row of the reconstructed approximate signal matrix is used as the reference subcarrier, and the remaining rows are used as information subcarriers. Based on the reference subcarrier, correlation detection is performed on all information subcarriers one by one.

[0115] Specifically, the obtained Line 1 As the recovered reference subcarrier, the rest As The reference subcarrier is correlated with each information subcarrier:

[0116]

[0117] in, represents the real part operation, Indicates the transposition operation of its reference signal. Indicates that the correlation value between the reference signal and the information signal is obtained by the inner product between the two ;

[0118] Step 7.3: Make a hard decision based on the positive or negative value of the correlation detection result and output a polarity symbol stream;

[0119] Specifically, based on the correlation value , make a hard decision based on the positive or negative correlation value to determine the corresponding polarity modulation symbol, ,in Indicates a hard decision on the correlation value, that is, demodulating the polarity modulation symbol from the positive and negative correlation values:

[0120]

[0121] Step 7.4: Restore the polar symbol stream to a serial stream and convert it back to the original information bits to complete demodulation.

[0122] Specifically, the demodulated polar modulation symbols are combined into a serial stream, and then the polar Convert back Information bits are used to complete the final data recovery.

[0123] Based on the above OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption, the present invention also proposes an OFDM-DCSK modulation and demodulation system based on chaotic masking and diffusion scrambling encryption, which mainly includes a transmitting end modulator and a receiving end demodulator.

[0124] The transmitter modulator in the modulation and demodulation system is as follows Figure 2 As shown, it includes a polarity converter, a serial-to-parallel converter, a chaotic signal generator, a chaotic masking module, a chaotic encryption module, a carrier multiplier, an inverse fast Fourier transformer and a parallel-to-serial converter.

[0125] The polarity converter is used to perform polarity modulation on the input serial information bit stream, mapping 0 to +1 and bit 1 to the polarity symbol of -1;

[0126] The serial-to-parallel converter parallelizes the serial polar symbol stream into N polar modulation symbols;

[0127] The chaotic signal generator generates a discrete chaotic signal sequence within a symbol period based on a preset chaotic map, and the generated discrete chaotic signal sequence is pulse-shaped to obtain a corresponding DCSK reference signal;

[0128] The chaotic masking module disperses and hides the reference chaotic sequence into N polar modulation symbol streams according to the diagonal insertion rule to generate a masked information sequence;

[0129] The chaotic encryption module includes a diffusion module and a scrambling module. The diffusion module is used to perform element-by-element expansion processing on the masked information sequence based on the chaotic key sequence. The diffusion module generates a chaotic key stream whose length matches the data amount and gradually accumulates each data element with the key stream value to achieve a diffusion operation. This makes the value of each symbol not only dependent on the current data itself, but also affected by the previous diffusion results and the chaotic key, thereby increasing the expansion correlation and unpredictability between data. The scrambling module first sorts the elements of the diffused matrix in the row direction according to the pre-generated chaotic key matrix, and reverses the index of the even-numbered rows according to the set rules to break the original element arrangement order. Then, a similar scrambling operation is performed in the column direction, and the even-numbered columns are reversed again.

[0130] The carrier multiplier maps the diffused and scrambled information sequence to the corresponding subcarrier frequency;

[0131] The inverse fast Fourier transformer performs an inverse transform on the frequency domain modulation symbols to generate an orthogonal time domain signal;

[0132] The parallel-to-serial converter combines the parallel time domain signals output by each subcarrier into a serial signal and transmits it to the channel.

[0133] The receiving end demodulator in the modulation and demodulation system is as follows Figure 3 As shown, it includes a serial-to-parallel converter, a fast Fourier transformer, a chaos decryption module, a chaos masking module, a singular value auxiliary module, a correlator, a decision device and a parallel-to-serial converter.

[0134] The fast Fourier transformer transforms the time domain signal into frequency domain subcarrier symbols;

[0135] The de-chaotic encryption module is used to sequentially perform inverse scrambling and inverse diffusion processing on the received subcarrier information matrix to restore the original subcarrier arrangement structure before encryption by the transmitting end. The de-scrambling module first performs row inverse sorting on the subcarrier matrix after row scrambling and then performs column inverse sorting on the matrix after column scrambling according to the chaotic key matrix used by the transmitting end during scrambling, gradually restoring the correct arrangement order of the subcarriers in the frequency domain. The de-diffusion module uses a pre-shared chaotic diffusion key sequence and, according to the diffusion reverse calculation logic, gradually removes the interference components accumulated and superimposed during the diffusion process, and restores the original subcarrier amplitude information element by element.

[0136] The chaos demasking module strips off the reference signal and the information carrier according to the masking insertion rule, thereby extracting the reference component and the information component in the mixed signal;

[0137] The singular value auxiliary module is used to perform a singular value decomposition operation on the receiving matrix output by the de-chaos encryption module, decomposing the receiving matrix into multiple singular values and corresponding singular vector groups. After the decomposition is completed, the singular value auxiliary module screens out the largest singular value and its corresponding left and right singular vectors according to the order of the singular values, retaining only the principal component information related to the largest singular value. Then, the singular value auxiliary module reconstructs an approximate matrix with a rank of 1 based on the retained largest singular value and the corresponding singular vector, which is used to approximately represent the main effective signal part received, thereby suppressing the influence of noise interference on the detection performance of the system;

[0138] The correlator uses the reference subcarrier as a reference and performs correlation operations with each information subcarrier to obtain a correlation detection value;

[0139] The decision device makes a hard decision based on whether the correlation value is positive or negative, and outputs a corresponding polarity bit.

[0140] Furthermore, to verify the effectiveness of the present invention and improve the system confidentiality, anti-interference and transmission reliability, a specific example is given below to illustrate. This embodiment includes the following steps:

[0141] Step 1: Use Logistic mapping to generate discrete chaotic sequences, and the sequence length is set to , the number of subcarriers is set to , each subcarrier corresponds to an information modulated bit stream, and the total number of information bits is 128;

[0142] Step 2: Use a polar modulator to perform polarity mapping on the 128 information bits, mapping 0 to +1 and 1 to -1, to obtain 128 polarity modulated signals;

[0143] Step 3: The 128 polarity bit streams generated in step 2 are processed by a serial-to-parallel converter to generate 128 parallel polarity symbol streams. ;

[0144] Step 4: Generate a chaotic reference sequence of length 128 by the chaos generator And multiply each polar symbol stream element by element with the reference sequence to form the initial modulated information sequence ;

[0145] Step 5: Use diagonal chaotic masking to transform the reference sequence Distributed insertion into the 128-channel information modulation sequence;

[0146] Step 6: Diffusion is performed on the masked information sequence obtained in step 5. The Logistic key sequence is used in the diffusion process to recursively diffuse the elements in the information sequence;

[0147] Step 7: Perform scrambling on the diffused sequence. First, arrange the rows in ascending order (even rows are reversed) and then arrange the columns in descending order (even columns are reversed) according to the chaotic key matrix to complete the diffusion scrambling encryption.

[0148] Step 8: Map the 128 encrypted information sequences after diffusion scrambling onto 128 orthogonal subcarriers respectively ;

[0149] Step 9: Input the subcarrier signal obtained in step 8 into the inverse fast Fourier transformer (IFFT) to transform the frequency domain symbols into the time domain and achieve mutual orthogonality between the subcarriers;

[0150] Step 10: Combine the 128 IFFT output time domain signal streams into one serial signal through a parallel / serial converter to form the transmit signal , and sent via the AWGN channel.

[0151] At the receiving end, the received signal is received and demodulated, including:

[0152] Step 11: The receiving end first converts the received serial signal through a serial-to-parallel converter Convert back to 128 parallel subcarrier signals;

[0153] Step 12: Perform a Fast Fourier Transform (FFT) on the parallel subcarrier signals to transform the time domain signal into the frequency domain and extract the frequency domain subcarrier components. ;

[0154] Step 13: Perform an inverse scrambling operation on the frequency domain signal to restore the correct arrangement order of each subcarrier; then perform an inverse diffusion process to restore the data structure before diffusion;

[0155] Step 14: Separate the reference information from the data information in each subcarrier signal according to the masking insertion rule and extract the hidden reference sequence. ;

[0156] Step 15: Perform singular value decomposition (SVD) on the recovered received matrix:

[0157]

[0158] Only the principal component of rank 1 corresponding to the largest singular value is retained for reconstruction, noise interference is suppressed, and an approximate matrix of rank 1 is obtained. ;

[0159] Step 16: Take the first row as the reference subcarrier and perform correlation detection with the information subcarriers of the remaining rows to obtain Related values:

[0160]

[0161] Step 17: Based on Correlation values The symbol performs hard decision and recovers 128 polarity modulation bits;

[0162] Step 18: Convert the 128-way decision bit stream back into a serial information bit stream through a parallel-to-serial converter, and finally convert the polarity bit stream into a serial information bit stream through a polarity demodulator. Restore to original bits , completing the entire receiving and demodulation process.

[0163] The present invention verifies the transmission performance of the present invention through computer simulation. In the experiment, the reference signal sequence of the modulation stage is mapped by Logistic generate, Indicates the The iterated value in the system, represents the control parameter, Indicates the value of the next iteration. In this experiment, the initial value of the chaotic system iteration is , control parameters , the signal-to-noise ratio is set to , set the sampling point at each signal-to-noise ratio to ,according to Figure 4 The results of the bit error rate (BER) of the method of the present invention in the additive white Gaussian noise channel (AWGN) environment are recorded in Table 1.

[0164] Table 1 Comparison of bit error rate performance of different methods under the same signal-to-noise ratio ( , )

[0165] As can be seen from the above table, compared with the traditional OFDM-DCSK method, the present invention achieves a lower bit error rate under the same signal-to-noise ratio conditions, showing better error performance.

[0166] Based on the above analysis, this invention further optimizes spectrum utilization efficiency while optimizing traditional security mechanisms. Furthermore, addressing the existing issues of reference signal vulnerability and weak system security, this invention significantly enhances system security through chaotic masking and encryption mechanisms, improving overall communication reliability and anti-interference capabilities.

[0167] The above describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. An OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption, characterized in that: The following steps are involved: Step 1: Polarity modulation and serial / parallel conversion are performed on the signal to be transmitted to form multiple parallel polarity symbol streams; Step 2: Generate a discrete chaotic sequence as a reference sequence based on a preset chaotic map, and multiply it element-by-element with the multiple parallel polarity symbol streams to obtain a multi-channel modulation information sequence; Step 3: Embed the reference sequence into the multi-channel modulated information sequence to achieve chaotic masking, and then perform chaotic diffusion and scrambling operations on the chaotically masked modulated information sequence in sequence to obtain the encrypted multi-channel diffusion scrambled information sequence; Step 4: The encrypted multi-path diffusion scrambled information sequence is mapped to several orthogonal subcarriers. After frequency domain to time domain conversion via inverse fast Fourier transform, it is synthesized into a serial signal and transmitted to the communication channel to complete signal modulation. Step 5: After receiving the serial signal from the communication channel, it is restored to multiple parallel subcarrier signals, and the time domain parallel subcarrier signals are restored to the frequency domain representation through fast Fourier transform to obtain the frequency domain received signal; Step 6: Perform inverse scrambling and inverse chaos diffusion operations on the frequency domain received signal in sequence to restore the signal structure before encryption. The restored signal is extracted and restored based on the known reference sequence to obtain the multi-channel modulation information sequence. Step 7: Perform singular value decomposition on the recovered multi-channel modulation information sequence, perform correlation detection based on the singular value decomposition result, perform hard decision according to the result of the correlation detection, and realize signal demodulation based on the result of the hard decision.

2. The OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption according to claim 1, characterized in that: The step 1 is specifically as follows: Step 1.1: Polarity modulate the input N serial information bits, and output a {1,−1} symbol sequence, where 0 is mapped to +1 and 1 is mapped to −1, resulting in N serial polarity modulated bits. Step 1.2: Convert the serial N polar modulation bits into N parallel polar symbol data streams in parallel.

3. The OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption according to claim 1, characterized in that: The step 3 is specifically as follows: Step 3.1: Embed the reference sequence diagonally into the N modulation information sequences to achieve chaotic masking and ensure that the reference sequence is not exposed, thereby obtaining N modulation information sequences containing the reference sequence. Step 3.2: Perform a chaotic diffusion operation on the N modulated information sequences including the reference sequence; Step 3.3: Perform a scrambling operation on the modulated information sequence after the chaotic diffusion operation based on the chaotic key matrix to complete spatial disturbance and obtain N encrypted multi-path diffusion scrambled information sequences.

4. The OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption according to claim 1, characterized in that: The step 3.2 is specifically as follows: A chaotic key sequence with the same dimension as the N modulation information sequences containing the reference sequence is obtained through chaotic mapping ; Select the last key element of the chaotic key sequence as the initial diffusion value, and modulate the N information sequences containing the reference sequence. For each element in , the chaotic diffusion operation is completed recursively as follows: ； in, Indicates the first elements, represents the value after diffusion, Indicates the value of the previous diffusion, the initial diffusion value is , Indicates the Chaotic key sequence value; The chaotic diffusion values are rearranged according to the size of the N modulation information sequences containing the reference sequence to obtain the matrix ,in, Indicates that the matrix will be obtained according to The dimension is reshaped, Representation matrix dimension.

5. The OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption according to claim 1, characterized in that: The step 3.3 is specifically as follows: A chaotic key matrix with the same dimension as the modulated information sequence after the chaotic diffusion operation is obtained through chaotic mapping; The elements of each row in the modulated information sequence after the chaotic diffusion operation are sorted in ascending order according to the odd rows corresponding to the chaotic key matrix, and the even rows are reversed in index order; Each column element in the modulated information sequence after the chaotic diffusion operation is sorted in descending order according to the odd columns corresponding to the chaotic key matrix, and the even columns are reversed in index order to obtain N encrypted multi-path diffusion scrambled information sequences.

6. The OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption according to claim 1, characterized in that: The step 4 is specifically as follows: Step 4.1: Map the encrypted N multi-channel diffusion scrambled information sequences onto N pre-defined orthogonal subcarriers to form frequency domain subcarrier signals, where each orthogonal subcarrier carries a corresponding diffusion scrambled information sequence; Step 4.2: All frequency-domain subcarrier signals are transformed into orthogonal time-domain subcarrier signals through inverse fast Fourier transform (IFFT). This ensures that the subcarrier signals are orthogonal to each other in the time domain and are not subject to inter-subcarrier interference. The N time-domain subcarrier signals are then combined into a serial signal and sent to the communication channel to complete the transmission.

7. The OFDM-DCSK modulation and demodulation method based on chaotic masking and diffusion scrambling encryption according to claim 1, characterized in that: The step 7 is specifically as follows: Step 7.1: Perform singular value decomposition on the recovered multi-channel modulation information sequence, retain only the largest singular value and its corresponding singular vector, and reconstruct an approximate signal matrix with rank 1; Step 7.2: The first row of the reconstructed approximate signal matrix is used as the reference subcarrier, and the remaining rows are used as information subcarriers. Based on the reference subcarrier, correlation detection is performed on all information subcarriers one by one. Step 7.3: Make a hard decision based on the positive or negative value of the correlation detection result and output a polarity symbol stream; Step 7.4: Restore the polar symbol stream to a serial stream and convert it back to the original information bits to complete demodulation.

8. An OFDM-DCSK modulation and demodulation system based on chaotic masking and diffusion scrambling encryption, characterized in that: include: Transmitter modulator: used to modulate the signal to be transmitted; Receiver demodulator: used to receive the modulated signal and demodulate it.

9. The OFDM-DCSK modulation and demodulation system based on chaotic masking and diffusion scrambling encryption according to claim 8, characterized in that: The transmitting end modulator specifically includes: Polarity converter: used to perform polarity modulation on the input serial information bit stream, mapping bit 0 to +1 and bit 1 to -1, generating a polarity symbol; Serial-to-parallel converter: used to parallelize the serial polar symbol stream into N polar modulation symbol streams; Chaotic signal generator: used to generate a discrete chaotic signal sequence within a symbol period based on a preset chaotic map; Chaotic masking module: used to disperse and embed the reference chaotic sequence into the N-channel polar modulation symbol stream according to the diagonal insertion rule to form a masked information sequence; Chaotic encryption module: includes a diffusion module and a scrambling module. The diffusion module is used to perform element-by-element expansion processing on the masked information sequence, and the scrambling module is used to perform row and column scrambling processing according to the chaotic key matrix to generate an encrypted information sequence. Carrier multiplier: used to map the encrypted information sequence to the corresponding N subcarrier frequencies; Inverse Fast Fourier Transformer: used to inversely transform the frequency domain subcarrier signal into an orthogonal time domain signal; Parallel-to-serial converter: used to combine the parallel time domain signals output by each subcarrier into a serial signal and send it to the communication channel.

10. The OFDM-DCSK modulation and demodulation system based on chaotic masking and diffusion scrambling encryption according to claim 8, characterized in that: The receiving end demodulator specifically includes: Serial-to-parallel converter: used to convert the received serial time domain signal into N parallel subcarriers; Fast Fourier Transformer: used to transform the parallel subcarrier time domain signals into frequency domain subcarrier symbols; Chaotic encryption decryption module: including descrambling module and de-diffusion module, which is used to perform inverse scrambling and inverse diffusion operations in sequence to restore the original subcarrier structure before encryption; Chaos demasking module: used to remove the reference signal and information signal from the recovered subcarrier signal according to the diagonal insertion rule; Singular value auxiliary module: used to perform singular value decomposition on the recovered matrix, retain the maximum singular value and its corresponding singular vector, and reconstruct an approximate matrix with rank 1 to suppress the influence of channel noise; Correlator: used to extract the correlation detection value between the reference subcarrier and each information subcarrier; Decision maker: used to perform hard decision based on the positive or negative correlation value and output the corresponding polarity bit; Parallel-to-serial converter: used to combine polarity bits into a recovered information bit stream for serial output.

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