Multi-user encrypted data transmission method based on DCSK and CDMA

Abstract

The invention belongs to the technical field of wireless communication and information security, and particularly relates to a multi-user encrypted data transmission method based on DCSK and CDMA, which comprises the following steps: constructing a DSCK-CDMA system, converting a bit signal sent by each user into an encrypted signal by a transmitting end through a chaotic signal and pseudo-random code combination module, and transmitting the encrypted signal to a receiving end; combining the encrypted signals of the plurality of users into a multi-user transmission signal and then sending out the multi-user transmission signal; transmitting a multi-user transmission signal by adopting an additive white Gaussian noise channel model; a receiving end carries out time-frequency synchronization processing on the received receiving signal through a time-frequency domain synchronization module; the interference suppression and multi-user detection module carries out reduction processing on the synchronously processed receiving signals; according to the invention, efficient and safe multi-user data transmission can be realized in a complex wireless communication environment.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communication and information security, and in particular relates to a multi-user encrypted data transmission method based on DCSK and CDMA. Background Art

[0002] With the continuous development of wireless communication and information technology, the demand for multi-user encrypted data transmission is increasing, especially in application scenarios such as the Internet of Things, wireless monitoring, and telemedicine. In order to achieve efficient and secure data transmission in complex and changeable wireless channels, differential chaotic shift keying (DCSK) and code division multiple access (CDMA) technologies have played an important role. However, the combination of these two technologies in a multi-user environment still faces many technical challenges.

[0003] DCSK is a modulation technology based on chaotic signals. Its characteristics are that it uses the randomness and non-periodicity of chaotic signals to modulate data. It has good anti-interference ability and is especially suitable for wireless channels with significant multipath effects. Another advantage of DCSK is non-coherent detection, that is, the receiver does not need to be strictly synchronized with the transmitter. This makes DCSK perform well in complex wireless communication environments. However, DCSK itself has certain limitations in multi-user scenarios, especially the non-orthogonality of chaotic signals can easily cause interference in multi-user communications, resulting in signal aliasing and increased bit error rate. In addition, although DCSK has excellent anti-interference performance, it is difficult to effectively separate the signals of multiple users in multi-user communications by relying solely on DCSK. In particular, when there is no suitable multi-user separation mechanism, the interference problem will become more serious.

[0004] On the other hand, CDMA is a technology that spreads signals through pseudo-random codes and is widely used in multi-user communication systems. CDMA can support simultaneous communication of multiple users within the same spectrum. It achieves separation of multi-user signals through the orthogonality of pseudo-random codes, ensuring that the signals of each user can be effectively distinguished. The advantages of CDMA are high spectrum utilization and strong multi-user signal separation capabilities, which are particularly suitable for application scenarios where multiple users communicate concurrently. However, CDMA technology has high requirements for synchronization, especially in multi-user scenarios. The synchronization process of pseudo-random codes is complex, and the anti-interference ability is weaker than DCSK, and it performs poorly when facing complex wireless channels. In addition, CDMA's pseudo-random codes have certain deficiencies in security and are easily cracked, affecting the privacy of data transmission.

[0005] Combining DCSK and CDMA is a reasonable technical choice because their respective advantages can complement each other. DCSK can enhance CDMA's anti-interference ability, while CDMA can solve the signal separation problem of DCSK in multi-user scenarios. However, this combination is not a simple superposition, but there are many technical difficulties to overcome. First, the difference in modulation methods is a key issue. DCSK's chaotic signal is non-orthogonal, while CDMA's pseudo-random code relies on the orthogonality of the signal. Direct combination will lead to incompatible modulation of the signal and increased interference. Second, multi-user interference (MAI) is another challenge. In the process of multi-user transmission, the randomness of DCSK signals aggravates the interference between different users, and the traditional CDMA pseudo-random code separation mechanism cannot effectively cope with this complex interference environment. Finally, the synchronization problem cannot be ignored. DCSK reduces the synchronization requirements due to its non-coherent detection technology, while CDMA relies on a strict synchronization mechanism for signal separation, which makes the two have a large difference in synchronization and increases the complexity of system design.

[0006] Although existing technologies combine DCSK and CDMA in certain specific applications, they still cannot effectively solve these core problems. Many solutions perform poorly in complex multi-user environments, especially in terms of synchronization, interference suppression and user signal separation. Summary of the invention

[0007] The present invention aims to solve the modulation incompatibility, multi-user interference and synchronization problems in the process of combining DCSK and CDMA, and proposes a multi-user encrypted data transmission method based on DCSK and CDMA, which is particularly suitable for many-to-one multi-user communication scenarios.

[0008] The specific plan includes the following steps:

[0009] S1. Construct a DSCK-CDMA system, which includes a transmitter, a receiver, a chaotic signal and pseudo-random code combination module, an interference suppression and multi-user detection module, and a time-frequency domain synchronization module;

[0010] S2. The transmitter converts the bit signal sent by each user into an encrypted signal through a chaotic signal and a pseudo-random code combination module, and combines the encrypted signals of multiple users into a multi-user transmission signal and then sends it out;

[0011] S3. Adopting additive white Gaussian noise channel model to transmit multi-user transmission signal;

[0012] S4. The receiving end performs time-frequency synchronization processing on the received signal through the time-frequency domain synchronization module;

[0013] S5. The interference suppression and multi-user detection module restores the received signal after synchronization processing.

[0014] Furthermore, the chaotic signal and pseudo-random code combination module includes a four-wing chaotic oscillator, a DCSK modulation unit and a CDMA unit; in step S2, the chaotic signal and pseudo-random code combination module modulates the bit signal b sent by user i. k The encryption process of ∈{-1,1} includes:

[0015] S21. Generate a chaotic signal x using a four-wing chaotic oscillator k (t), for the chaotic signal x k (t) Sampling to obtain random signal p k ∈{-1,1};

[0016] S22. The bit signal b k With the random signal p k Perform XOR operation to obtain random bit signal xb k ∈{-1,1};

[0017] S23. In the CDMA unit, the random bit signal xb k and the channel coded signal c k ∈{-1,1} performs XOR operation to obtain the coded signal a k ∈{-1,1};

[0018] S24.DSCK modulation unit according to the chaotic signal x k (t) and the coded signal a k Generate encrypted signal u k (t);

[0019] S25. Encrypt the signal u k (t) CDMA pseudo-random code P corresponding to user i i (t) combined to obtain the transmission signal s i (t).

[0020] Further, step S24 specifically includes:

[0021] The chaotic signal x k (t) Delay T b / 2,T b Bit b k The width of the delayed chaotic signal and the coded signal a k Multiply the encrypted information and the chaotic signal x k (t) Combine and generate encrypted signal u k (t).

[0022] Furthermore, the signal after the multi-user transmission signal is transmitted through the additive white Gaussian noise channel model is expressed as

[0023]

[0024] Where N is the number of concurrent users, n(t) is the additive Gaussian white noise, and s i (t) represents the transmission signal of user i.

[0025] Furthermore, step S4 performs time-frequency synchronization processing on the received signal through the time-frequency domain synchronization module, including:

[0026] S41. Correlation detection is performed on the received signal and the CDMA pseudo-random code of each user to obtain the corresponding correlation value, and the time corresponding to the maximum correlation value is used as the starting time for time domain synchronization;

[0027] S42. Calculate and estimate the frequency offset between the multi-user transmission signal and the received signal, and perform frequency compensation on the received signal according to the frequency offset.

[0028] Furthermore, step S5 specifically includes:

[0029] S51. The received signal after time-frequency synchronization processing is used as the initial total signal;

[0030] S52. Based on the total signal, a parallel interference elimination algorithm is used to obtain the restored transmission signal s of user i. i '(t);

[0031] S53. Perform correlation analysis on the restored transmission signal to obtain the restored coded signal a k ';

[0032] S54. Restore the coded signal a k ' and the channel coded signal c k Perform XOR operation to obtain the restored random bit signal xb k ';

[0033] S55. Restore the random bit signal xb k 'With random signal p k Perform XOR operation to restore the bit signal b k ;

[0034] S56. According to the bit signal b k The detected signal is calculated, and after the total signal is updated by the detected signal, i=i+1 is set, and steps S52-S56 are repeated until the restored bit signals of all users are demodulated.

[0035] Furthermore, in step S52, based on the total signal, a parallel interference elimination algorithm is used to obtain the restored transmission signal s of user i. i '(t), including:

[0036] S521. Initialize the number of iterations m = 0, and take the current total signal as the interference cancellation signal of user i in the 0th iteration;

[0037] S522. According to the CDMA pseudo-random code P of user i i (t) is estimated to obtain the estimated restored signal of user i in the mth iteration Expressed as

[0038]

[0039] S523. Calculate the interference amount of user i in the mth iteration Expressed as

[0040]

[0041] in, The estimated restored signal of user j at the mth iteration;

[0042] S524. Calculate the interference cancellation signal of user i in the mth iteration Expressed as

[0043]

[0044] S525. Determine the interference cancellation signal of the mth iteration and the interference cancellation signal of the m-1th iteration Is the difference between them less than a preset threshold? If so, the current estimated restored signal is used as the restored transmission signal output; if not, set m=m+1 and return to step S522.

[0045] Further, step S56 is performed according to the bit signal b k Calculate the detected signal and update the total signal by the detected signal, which is expressed as

[0046] R new-all (t) = R all (t)-(b k ·P i (t))

[0047] Among them, R all (t) represents the total signal before updating, R new-all (t) represents the updated total signal.

[0048] Beneficial effects of the present invention:

[0049] The present invention combines differential chaotic shift keying (DCSK) with code division multiple access (CDMA) technology to propose an efficient solution suitable for multi-user encrypted data transmission. The chaotic modulation of DCSK technology enhances the data encryption performance of the system, while the pseudo-random code of CDMA realizes the separation and spread spectrum of multi-user signals, thereby improving the anti-interference ability and data security of the system. The introduction of a chaotic signal and pseudo-random code combination module solves the incompatibility of the two in modulation mode. By designing an interference suppression and multi-user detection module, the multi-user interference problem is effectively dealt with; and by using a time-frequency domain synchronization module, the differences between DCSK and CDMA in synchronization mechanism are coordinated to ensure efficient separation and low bit error rate demodulation of multi-user signals during transmission, and avoid signal distortion caused by synchronization errors. The present invention can realize efficient and secure multi-user data transmission in a complex wireless communication environment, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a flow chart of the method of the present invention;

[0051] Figure 2 A schematic diagram of data encryption using DCSK combined with CDMA technology in the present invention;

[0052] Figure 3 This is a flow chart of the chaotic demodulation combined with CDMA technology for data decryption in the present invention. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] The present invention provides a multi-user encrypted data transmission method based on DCSK and CDMA, which is particularly suitable for data encryption and transmission in a multi-user environment. The present invention effectively solves the technical difficulties encountered in the process of combining DCSK and CDMA by designing multiple key modules, including modulation compatibility, multi-user interference suppression and synchronization problems, thereby realizing efficient and secure multi-user data transmission.

[0055] like Figure 1 As shown, the scheme includes the following steps:

[0056] S1. Construct a DSCK-CDMA system, which includes a transmitter, a receiver, a chaotic signal and pseudo-random code combination module, an interference suppression and multi-user detection module, and a time-frequency domain synchronization module.

[0057] S2. The transmitter converts the bit signal sent by each user into an encrypted signal through a chaotic signal and pseudo-random code combination module, and combines the encrypted signals of multiple users into a multi-user transmission signal and then sends it out.

[0058] Specifically, the present invention assumes that the data sent by each user is image data, and their image data is mapped into independent binary bit streams. Each binary bit stream is encrypted and modulated by DCSK and CDMA before transmission, and then the encrypted signals of all users are combined and transmitted. For a user, the image data to be sent is first converted into a binary bit stream according to the conversion operation. Each pixel of the image data occupies 1 byte, that is, the bit depth of each pixel is 8 bits (i.e., the gray value between 0 and 255), and each pixel value will be converted into a binary sequence with a length of 8.

[0059] Image data can be converted to a binary bit stream using Matlab tools, including:

[0060] S11. Use the imread function of Matlab to read the image data. This function reads the image data as an image matrix, and each element in the image matrix represents a pixel value of the image. It should be noted that if the image data read is a color image, you can first use the rgb2gray function to convert it into a grayscale image, so that each pixel only occupies one byte, which is convenient for subsequent conversion into a bit stream.

[0061] S12. Use the reshape function to convert the image matrix into a one-dimensional vector, and then execute step S13;

[0062] S13. The pixel value of each pixel can be converted into an 8-bit binary number using the dec2bin function;

[0063] S14. concatenate the binary numbers of each pixel to form a complete binary bit stream. Here, vercat or horcat function can be used for concatenation.

[0064] S15. Use the fwrite function to save the binary bit stream as a binary file.

[0065] Specifically, the main function of the chaotic signal and pseudo-random code combination module is to combine the DCSK modulation signal with the CDMA pseudo-random code to form an encrypted and scalable transmission signal, solving the incompatibility between DCSK and CDMA in modulation mode. The chaotic signal and pseudo-random code combination module includes a four-wing chaotic oscillator, a DCSK modulation unit and a CDMA unit.

[0066] The present invention uses a four-wing chaotic oscillator as a source of chaotic signal generation. The four-wing chaotic oscillator is widely used in information encryption and secure communication due to its complex dynamic behavior and good randomness. The four-wing chaotic oscillator is described by a set of differential equations:

[0067]

[0068] Among them, x, y, and z are the dependent variables of the four-wing chaotic oscillator system. is the dependent variable x,

[0069] The first-order derivatives of y and z, and a', b', c', d', e', and f' are the parameters of the four-wing chaotic oscillator system. In order to numerically evaluate the four-wing chaotic oscillator system and generate waveforms, the fourth-order Runge-Kutta numerical method (RK4) is used. When the RK4 method is applied to equation (1), it becomes equation (2):

[0070]

[0071] Where K 1x , K 2x Various symbols K are slope estimates at different points in the Runge-Kutta method, which are used to gradually approximate the solution. h is the step size in the RK4 method, and its size determines the accuracy and computational complexity of the numerical integration. In the fourth-order Runge-Kutta numerical integration process of the present invention, the step size h=0.001 is selected to ensure that the generated chaotic signal has sufficient accuracy and randomness to meet the system's high-precision requirements for encrypted signals. The subscript i in this formula represents the current iteration step index, which is used to identify the state of the i-th step. As each iteration proceeds, the state index i will gradually increase, thereby updating the state variables of the system. The generated chaotic signal can be used in the subsequent DCSK modulation process and combined with the image data for encryption.

[0072] The CDMA unit uses code division multiple access (CDMA) technology to perform preliminary processing on the image data. CDMA is a broadband technology used for multi-channel communication. Information is encrypted through channel coding. Each channel is assigned an extension code of length M. After the original information is encrypted by CDMA, its bandwidth increases and its power decreases.

[0073] The DCSK modulation unit uses DCSK technology to perform chaotic modulation on the data. DCSK is a chaotic digital modulation technology suitable for incoherent detection, which does not require strict synchronization between the receiving end and the transmitting end. Its modulation signal mainly consists of two parts: one part is the reference chaotic signal, and the other part is the data signal carrying information. For each bit b k, it is mapped into two time periods, where the first time period is the reference time slot, used to transmit the reference chaotic signal, and the second time period is the data time slot, used to transmit the data signal determined by the data bit value. The specific formula is as follows:

[0074]

[0075] Among them, T b Bit b k The width of <T b / 2, the first time period of the modulated signal represents the carrier reference. b / 2≤t≤T b The second time period is the same as bit b k Related data signals.

[0076] Specifically, in step S2, the chaotic signal and pseudo-random code combination module processes the bit signal b sent by user i. k ∈{-1,1} for encryption processing, such as Figure 2 As shown, including:

[0077] S21. Generate a chaotic signal x using a four-wing chaotic oscillator k (t), for the chaotic signal x k (t) Sampling to obtain random signal p k ∈{-1,1};

[0078] S22. The bit signal b k With the random signal p k Perform XOR operation to obtain random bit signal xb k ∈{-1,1};

[0079] S23. In the CDMA unit, the random bit signal xb k and the channel coded signal c k ∈{-1,1} performs XOR operation to obtain the coded signal a k ∈{-1,1};

[0080] S24.DSCK modulation unit according to the chaotic signal x k (t) and the coded signal a k Generate encrypted signal u k (t);

[0081] Specifically, the chaotic signal is divided into a reference segment and a data segment. b / 2≤t≤T b When the chaotic signal is combined with the coded signal a k Multiply the encrypted information by the chaotic signal x k(t) Combine and generate encrypted signal u k (t).

[0082] S25. Encrypt the signal u k (t) CDMA pseudo-random code P corresponding to user i i (t) combined to obtain the transmission signal s i (t).

[0083] The above method is suitable for discrete data processing scenarios, especially for encryption of images, files or other forms of binary data. This combination ensures the encryption characteristics of DCSK, while using the pseudo-random code of CDMA to achieve effective separation and expansion of multi-user signals. The modulated signal has good anti-interference and anti-noise capabilities.

[0084] S3. Use additive white Gaussian noise channel model to transmit multi-user transmission signals.

[0085] Specifically, in step S2, the image data after DCSK modulation and CDMA encoding has been encrypted into a multi-user transmission signal suitable for multi-user transmission. The multi-user transmission signal is transmitted concurrently in a multi-user environment through a wireless channel. In a wireless channel, the signal may be subject to various interferences, such as multipath effect, additive white Gaussian noise (AWGN), fading effect, etc. These interference factors will affect the quality of the signal and the demodulation effect of the receiving end. This embodiment uses an additive white Gaussian noise (AWGN) channel model to model the transmission of multi-user transmission signals. Its mathematical expression is:

[0086]

[0087] Where N is the number of concurrent users; n(t) is the additive Gaussian white noise, which simulates the noise interference in the channel; s i (t) represents the transmission signal of user i.

[0088] By performing non-coherent detection on R(t) at the receiving end, the correlation between the data segment and the reference segment can be extracted to restore the original bit information. At the same time, the orthogonal characteristics of CDMA pseudo-random codes ensure that the signals of each user are mutually orthogonal in the spectrum, so that multiple users can transmit concurrently in the same frequency band, ensuring the separation of signals between users.

[0089] S4. The receiving end performs time-frequency synchronization processing on the received signal through the time-frequency domain synchronization module.

[0090] Specifically, one advantage of DCSK is its non-coherent detection, which does not require the transmitter and receiver to strictly synchronize the phase of the signal. However, the CDMA system has high requirements for the synchronization of pseudo-random codes. It must ensure that the pseudo-random codes of different users are accurately synchronized at the receiving end, otherwise it will affect the effect of signal separation. If the synchronization is inaccurate, multiple user signals will interfere with each other, resulting in signal demodulation failure. Therefore, time-frequency domain synchronization is the key to ensuring system performance. The first task of the receiving end is to recover and synchronize the signal from the wireless channel to ensure that the transmitter and receiver are consistent in the time domain and frequency domain. Step S4 performs time-frequency synchronization processing on the received signal through the time-frequency domain synchronization module, including:

[0091] S41. Perform correlation detection on the received signal and the CDMA pseudo-random code of each user to obtain corresponding correlation values, and perform time domain synchronization with the time corresponding to the maximum correlation value as the starting time.

[0092] Specifically, the correlation value between the received signal and the CDMA pseudo-random code of user i is obtained by correlation detection, which is expressed as

[0093]

[0094] C(τ) is the received signal R(t) and the CDMA pseudo-random code P i (t) related value.

[0095] When the CDMA pseudo-random code is subjected to correlation detection in a synchronized (aligned) state, its autocorrelation peak value will be significantly higher than the correlation value in an asynchronous state. Therefore, at the moment when the received signal is completely aligned with the CDMA pseudo-random code, the correlation value C(τ) will reach the maximum. In other words, the received signal is aligned with the user's CDMA pseudo-random code at this moment.

[0096] S42. Calculate and estimate the frequency offset between the multi-user transmission signal and the received signal, and perform frequency compensation on the received signal according to the frequency offset.

[0097] Specifically, in order to avoid the mismatch problem caused by frequency drift, the receiving end needs to estimate the frequency offset between the transmitted signal and the received signal. The frequency offset estimation formula used in the present invention is:

[0098]

[0099] Where △f is the estimated frequency offset. The receiving end performs frequency compensation on the received signal based on this value. The frequency compensation is expressed as:

[0100] R corrected (t) = R(t)·e -j2π△ft (7)

[0101] arg(R(t)) represents the instantaneous phase information of the received signal, R corrected (t) represents the received signal after frequency offset compensation. Through frequency compensation, the received signal can be consistent with the transmitted signal in the frequency domain, ensuring that the subsequent pseudo-random code demodulation can be performed correctly.

[0102] S5. The interference suppression and multi-user detection module restores the received signal after synchronization processing.

[0103] Specifically, after the time-frequency domain synchronization is completed, the receiving end separates and recovers the signal of each user through the interference suppression and multi-user detection module. Since the receiving end receives the superposition of multiple user signals, it is necessary to use interference suppression algorithm (parallel interference cancellation PIC) and multi-user detection technology (decision feedback detection DFD) to eliminate multiple access interference and decode the signals of each user.

[0104] The core idea of ​​the PIC algorithm is to eliminate interference signals between different users through iteration, thereby gradually improving the demodulation quality of each user's signal. The main process of PIC includes: initial estimation, interference elimination, and updated estimation. The PIC algorithm can effectively reduce the impact of MAI by processing the signals of multiple users in parallel during the interference suppression process, ensuring that the signal of each user can be accurately recovered in a noisy and interference environment. In the present invention, the receiving end uses a pseudo-random code to demodulate each user's signal and recovers the encrypted signal u of each user through an XOR operation. k (t), and then restore the original data according to the DCSK demodulation algorithm.

[0105] In order to further improve the accuracy of multi-user detection, the present invention introduces an improved multi-user decision feedback detection (DFD) algorithm, which ensures the detection accuracy of subsequent user signals by gradually eliminating the influence of detected user signals. The principle is mainly: first detect the signal of the first user and restore its data, then subtract the detected user signal from the total signal to reduce interference to other users, repeat the above process, detect the signals of the remaining users in turn, and gradually optimize the detection accuracy of each user. Through decision feedback detection (DFD), the system can accurately detect the signal of each user in a multi-user environment, especially in an interference environment. This method effectively reduces the interference of other user signals to the target user and greatly improves the detection accuracy.

[0106] Specifically, Figure 3 As shown, step S5 specifically includes:

[0107] S51. Use the received signal after time-frequency synchronization processing as the initial total signal.

[0108] S52. Based on the total signal, a parallel interference elimination algorithm is used to obtain the restored transmission signal s of user i.i '(t).

[0109] Specifically, step S52 uses a parallel interference elimination algorithm based on the total signal to obtain the restored transmission signal s of user i i '(t), including:

[0110] S521. Initialize the number of iterations m = 0, and take the current total signal as the interference cancellation signal of user i in the 0th iteration;

[0111] S522. According to the CDMA pseudo-random code P of user i i (t) is estimated to obtain the estimated restored signal of user i in the mth iteration Expressed as

[0112]

[0113] S523. Calculate the interference amount of user i in the mth iteration Expressed as

[0114]

[0115] in, The estimated restored signal of user j at the mth iteration;

[0116] S524. Calculate the interference cancellation signal of user i in the mth iteration Expressed as

[0117]

[0118] S525. Determine the interference cancellation signal of the mth iteration and the interference cancellation signal of the m-1th iteration Is the difference between the two values ​​less than a preset threshold value (the preset threshold value of the present invention is 10 -5 ), if yes, it is considered that the interference elimination has reached the system accuracy requirement, the iteration can be terminated, and the current estimated restored signal is output as the restored transmission signal; if not, set m=m+1 and return to step S522.

[0119] S53. Perform correlation analysis on the restored transmission signal to obtain the restored coded signal a k '.

[0120] Specifically, this step is achieved by performing correlation detection with the pseudo-random code used by the transmitter. When the modulated bit is high, t <T b / 2 segment and T b / 2≤t≤T b On the other hand, when the modulation bit is low, T b / 2≤t≤Tb The segments will be inverted relative to the horizontal axis. That is, by calculating the correlation between the reference time slot and the data time slot, the value of the data bit is determined. If the two time slot signals are the same, it means the bit is 1; if they are opposite, it means the bit is 0.

[0121] S54. Restore the coded signal a k ' and the channel coded signal c k Perform XOR operation to obtain the restored random bit signal xb k '.

[0122] S55. Restore the random bit signal xb k 'With random signal p k Perform XOR operation to restore the bit signal b k .

[0123] S56. According to the bit signal b k The detected signal is calculated, and after the total signal is updated by the detected signal, i=i+1 is set, and steps S52-S56 are repeated until the restored bit signals of all users are demodulated.

[0124] Step S56 is based on the bit signal b k Calculate the detected signal and update the total signal by the detected signal, which is expressed as

[0125] R new-all (t) = R all (t)-(b k ·P i (t))

[0126] Among them, R all (t) represents the total signal before updating, R new-all (t) represents the updated total signal.

[0127] After signal demodulation, the resulting binary bit stream needs to be reassembled into the original transmission data. In the image transmission scenario, the demodulator will output a binary bit stream corresponding to the image data. The binary bit stream needs to be reassembled according to the previous encoding method to recover the pixel information of the image. For grayscale images, 8 bits will be reassembled into the corresponding grayscale pixel values; for RGB images, 24 bits (8 bits per color channel) will be reassembled into RGB pixel values. The reassembled pixel values ​​are rearranged into a two-dimensional matrix according to the predetermined image resolution (such as 256x256 or 512x512). The grayscale value or color value of each pixel is extracted from the bit stream and filled into the corresponding image matrix by row and column to finally form a complete image matrix. Finally, the recovered image data is output as a standard image format, such as BMP, PNG or JPEG file. Users can view the image directly or further process the image for specific application scenarios, such as video surveillance, telemedicine, etc.

[0128] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "rotation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0129] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multi-user encrypted data transmission method based on DCSK and CDMA, characterized in that: The following steps are involved: S1. Construct a DSCK-CDMA system, which includes a transmitter, a receiver, a chaotic signal and pseudo-random code combination module, an interference suppression and multi-user detection module, and a time-frequency domain synchronization module; S2. The transmitter converts the bit signal sent by each user into an encrypted signal through a chaotic signal and a pseudo-random code combination module, and combines the encrypted signals of multiple users into a multi-user transmission signal and then sends it out; S3. Adopting additive white Gaussian noise channel model to transmit multi-user transmission signal; S4. The receiving end performs time-frequency synchronization processing on the received signal through the time-frequency domain synchronization module; S5. The interference suppression and multi-user detection module restores the received signal after synchronization processing.

2. A multi-user encrypted data transmission method based on DCSK and CDMA according to claim 1, characterized in that: The chaotic signal and pseudo-random code combination module includes a four-wing chaotic oscillator, a DCSK modulation unit and a CDMA unit; in step S2, the chaotic signal and pseudo-random code combination module modulates the bit signal b sent by user i k The encryption process of ∈{-1,1} includes: S21. Generate a chaotic signal x using a four-wing chaotic oscillator k (t), for the chaotic signal x k (t) Sampling to obtain random signal p k ∈{-1,1}; S22. The bit signal b k With the random signal p k Perform XOR operation to obtain random bit signal xb k ∈{-1,1}; S23. In the CDMA unit, the random bit signal xb k and the channel coded signal c k ∈{-1,1} performs XOR operation to obtain the coded signal a k ∈{-1,1}; S24.DSCK modulation unit according to the chaotic signal x k (t) and the coded signal a k Generate encrypted signal u k (t); S25. Encrypt the signal u k (t) CDMA pseudo-random code P corresponding to user i i (t) combined to obtain the transmission signal s i (t).

3. A multi-user encrypted data transmission method based on DCSK and CDMA according to claim 2, characterized in that: Step S24 specifically includes: The chaotic signal x k (t) Delay T b / 2,T b Bit b k The width of the delayed chaotic signal and the coded signal a k Multiply the encrypted information and the chaotic signal x k (t) Combine and generate encrypted signal u k (t).

4. The multi-user encrypted data transmission method based on DCSK and CDMA according to claim 1, characterized in that: The signal after multi-user transmission signal is transmitted through the additive white Gaussian noise channel model is expressed as Where N is the number of concurrent users, n(t) is the additive Gaussian white noise, and s i (t) represents the transmission signal of user i.

5. The multi-user encrypted data transmission method based on DCSK and CDMA according to claim 1, characterized in that: Step S4 performs time-frequency synchronization processing on the received signal through the time-frequency domain synchronization module, including: S41. Correlation detection is performed on the received signal and the CDMA pseudo-random code of each user to obtain the corresponding correlation value, and the time corresponding to the maximum correlation value is used as the starting time for time domain synchronization; S42. Calculate and estimate the frequency offset between the multi-user transmission signal and the received signal, and perform frequency compensation on the received signal according to the frequency offset.

6. The multi-user encrypted data transmission method based on DCSK and CDMA according to claim 1, characterized in that: Step S5 specifically includes: S51. The received signal after time-frequency synchronization processing is used as the initial total signal; S52. Based on the total signal, a parallel interference elimination algorithm is used to obtain the restored transmission signal s of user i. i '(t); S53. Perform correlation analysis on the restored transmission signal to obtain the restored coded signal a k '; S54. Restore the coded signal a k ' and the channel coded signal c k Perform XOR operation to obtain the restored random bit signal xb k '; S55. Restore the random bit signal xb k 'With random signal p k Perform XOR operation to restore the bit signal b k ; S56. According to the bit signal b k The detected signal is calculated, and after the total signal is updated by the detected signal, i=i+1 is set, and steps S52-S56 are repeated until the restored bit signals of all users are demodulated.

7. A multi-user encrypted data transmission method based on DCSK and CDMA according to claim 6, characterized in that: Step S52 uses a parallel interference elimination algorithm to obtain the restored transmission signal s of user i based on the total signal i '(t), including: S521. Initialize the number of iterations m = 0, and take the current total signal as the interference cancellation signal of user i in the 0th iteration; S522. According to the CDMA pseudo-random code P of user i i (t) is estimated to obtain the estimated restored signal of user i in the mth iteration Expressed as S523. Calculate the interference amount of user i in the mth iteration Expressed as in, The estimated restored signal of user j at the mth iteration; S524. Calculate the interference cancellation signal of user i in the mth iteration Expressed as S525. Determine the interference cancellation signal of the mth iteration and the interference cancellation signal of the m-1th iteration Is the difference between them less than a preset threshold? If so, the current estimated restored signal is used as the restored transmission signal output; if not, set m=m+1 and return to step S522.

8. The multi-user encrypted data transmission method based on DCSK and CDMA according to claim 6, characterized in that: Step S56 is based on the bit signal b k Calculate the detected signal and update the total signal by the detected signal, which is expressed as R new-all (t)=R all (t)-(b k ·P i (t)) Among them, R all (t) represents the total signal before updating, R new-all (t) represents the updated total signal.

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