A high-security joint modulation method for information transmission based on multi-constellation indexing

Abstract

The present invention relates to the field of communication technologies, and discloses a high-security joint modulation method for information transmission based on multi-constellation indexing, which includes the following steps. At the sending end, the 4D hyperchaotic model is used to perform bitwise XOR encryption on the original data of A randomly generated binary bit streams; perform serial-to-parallel conversion on the encrypted data; perform subcarrier and symbol scrambling on the converted data; then use the multi-constellation indexing joint modulation method to modulate the key that has been converted into binary, construct a key index matrix, and combine the index matrix with two QPSK modulation formats to obtain a transmitted signal; the transmitted signal is transmitted through an OFDM system; at the receiving end, the correct key is extracted through the constellation point position information of QPSK modulation, and the received signal is decrypted and demodulated using the extracted key to obtain the original data. The present invention can achieve synchronous high-security and high-performance transmission of the key accompanying signal.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and particularly to a high-security joint modulation method for information transmission based on multi-constellation indexing. Background Art

[0002] In recent years, with the rise of new services such as ultra-high-definition video, cloud computing, and virtual reality, there has been an explosive growth in mobile data traffic, which has put forward new requirements for information transmission capabilities. With the continuous increase in the amount of transmitted information and the continuous development of quantum computers, information is vulnerable to illegal eavesdropping or brute-force cracking during transmission. Therefore, how to effectively ensure the security of information transmission has become extremely important.

[0003] To ensure the security of information transmission, information encryption schemes are usually adopted. Currently, there are two mainstream encryption methods. One is encryption for the upper layer of network protocols. However, with the continuous increase in the number of users, this encryption method not only leads to a continuous increase in computational complexity but also faces the risk of brute-force cracking. The other is the encryption method for optical signals at the physical layer, whose security has been further improved and is currently the widely adopted encryption method. Quantum key distribution makes full use of quantum characteristics for encryption and can actively detect illegal attacks, so it is considered the most secure encryption method. However, due to its slow key generation rate, limitations in cost and technical means, etc., it has not been widely adopted. The chaotic encryption method based on digital signal processing technology (DSP) effectively overcomes the above deficiencies and is widely used in the encryption of communication systems due to its high sensitivity to the initial value of the key, high randomness of the chaotic system itself, and large key space.

[0004] For the chaotic encryption method based on DSP, it is default that the keys at both the sending and receiving ends are known, that is, the initial values of the shared chaotic model are known. However, once the key is deciphered by an illegal attacker, the security performance of the chaotic system will be greatly reduced, and even the information encryption effect will be lost. Moreover, the rapid increase in the number of users will inevitably lead to a rapid increase in the number of keys, and the management of such a large number of keys is also an urgent problem to be solved.

[0005] To solve the above problems, the method of transmitting keys along with signals has been proposed in the past two years. In this method, the key can be transmitted along with the information, realizing the dynamic change of the key. That is, for a chaotic system, its key is no longer fixed, but the sender can independently control the key value sent each time. Due to the continuous change of the key value, it brings great difficulties to the deciphering of illegal attackers. Related researchers have explored various ways of transmitting keys along with signals. For example, using the physical properties of the optical carrier itself to transmit keys, including using optical phase and optical polarization state to transmit keys. However, the above methods all require additional equipment and are difficult to be compatible with the existing optical communication system architecture. Recently, researchers have proposed a method of hiding the key in the noise and transmitting it along with the signal. Although this method solves the problem of incompatibility with the existing optical communication system architecture, too large noise power will reduce the signal transmission quality, and too small noise power will affect the correct extraction of the key. The method of hiding the key in the signal frame header for transmission avoids the influence of noise on the signal transmission quality, but due to the addition of the key in the frame header, it will cause redundant data processing when receiving the signal.

[0006] There are also some information transmission and modulation methods in the prior art, such as:

[0007] (1) The Chinese invention patent with the application number 202410591118.X and the name of "High Data Rate Hybrid Index Multi-Carrier Differential Chaos Keying Modulation and Demodulation Method and System Based on Scrambling" adopts the high data rate hybrid index multi-carrier differential chaos keying modulation and demodulation method based on scrambling, which can transmit reference signals and information signals within the same time period, thereby improving the data transmission rate, energy efficiency, spectral efficiency and confidentiality of the system; greatly reducing the noise component in the decision variable, thereby improving the bit error performance of the system, and thus being able to obtain a lower bit error rate than the MC-DCSK modulation and demodulation method.

[0008] (2) The Chinese invention patent with the application number 202310120533.2 and the name of "Covert Communication Method Based on Carrier Index Modulation and Hybrid Chaos Communication" takes the modulation bit as the plaintext information bit, and the sub-carrier index bit and the hybrid chaos information bit as the covert information bits. Using the carrier index modulation technology, it increases the channel capacity of the covert communication and can maintain a high achievable rate performance under any signal-to-noise ratio condition. The covert communication system therein can avoid the brute-force search process in the index modulation, greatly reducing the computational complexity of the system and promoting the efficiency of the modulation symbol detection and restoration work to a certain extent.

[0009] (3) Another example is a Chinese invention patent with the application number 202310275421.4 and the title "Reflection Constellation Point Optimization Method for an Intelligent Metasurface Index Modulation System". It can improve the system bit error rate performance while performing index modulation, overcome the problem that the index modulation scheme cannot have both high transmission information and low bit error rate transmission, improve the system transmission efficiency, and maintain a low bit error rate even in a low signal-to-noise ratio environment. However, it mainly uses an algorithm with high generality based on the K-means algorithm to optimize the reflection constellation points.

[0010] (4) A Chinese invention patent with the application number 202311467162.1 and the title "High-Dimensional Index Modulation Information Transmission Method and System Based on Space-Time Block Codes" can increase space diversity and time diversity under the condition of ensuring the system transmission rate remains unchanged, improve the transmission stability of the system, ensure the user service quality, and also eliminate interference in the process of receiving superimposed signals, improving the robustness of information transmission. However, it introduces space-time block codes into a high-dimensional index modulation OFDM-NOMA system and constructs a high-dimensional index modulation OFDM-NOMA system based on space-time block codes to implement it. The superimposed signal is generated by the superimposing module and the space-time encoder in the transmitting end. Summary of the Invention

[0011] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a high-security joint modulation method for information transmission based on multi-constellation indexing, which can achieve synchronous high-security and high-performance transmission of key adjoint signals. The key will neither affect the transmission performance of the effective information during the transmission process nor cause redundant data processing, ensuring the high-performance transmission of the key itself, with a low bit error rate, good transmission effect, and high information security.

[0012] The present invention is implemented by the following technical solutions: A high-security joint modulation method for information transmission based on multi-constellation indexing includes the following steps.

[0013] Step 1: At the transmitting end, use a 4D hyperchaotic model to perform bitwise XOR encryption on the original data of A-bit binary bit streams randomly generated to obtain a binary bit stream T after XOR scrambling.

[0014] The 4D hyperchaotic model is expressed as:

[0015]

[0016] Among them, X, Y, Z, and W are state variables, and a, b, c, d, and k are system parameters.

[0017] Step 2: Perform serial-to-parallel conversion on the encrypted data to generate a C×E matrix H.

[0018] Step 3: Subcarrier and symbol scrambling are performed on the converted data to generate a matrix P of C×E, completing the chaotic encryption process;

[0019] Step 4: Subsequently, the key that has been converted to binary is modulated using the multi-constellation index joint modulation method to construct a key index matrix, and the transmitted signal is obtained by combining the index matrix with two QPSK modulation formats;

[0020] Step 6: The transmitted signal is transmitted through an OFDM system;

[0021] Step 6: At the receiving end, the correct key is extracted through the constellation point position information of QPSK modulation, and the received signal is decrypted and demodulated using the extracted key to obtain the original data.

[0022] Furthermore, the bitwise XOR encryption method for the original data in Step 1 is as follows:

[0023] Using a 4D hyperchaotic model to process an original binary bit stream of A bits The following can be obtained:

[0024]

[0025] Among them, the chaotic sequences X(1) and X(3) each have A / 2 elements, which are generated by the state variables X and Z in the chaotic model respectively; X is a binary XOR bit stream of the same size as the original binary bit stream That is, X is also A bits and directly participates in The XOR scrambling; T is the finally obtained XOR-scrambled binary bit stream. Among them, T is determined by the parity of the fourth digit after the decimal point of the elements in the chaotic sequences X(1) and X(3), that is, odd is 1 and even is 0; floor(-) is the floor function, and mod(-) is the remainder function.

[0026] Furthermore, the process of serial-to-parallel conversion of the data in Step 2 is as follows,

[0027] Step 21: The binary data stream after bitwise XOR scrambling is transformed from the original 1×A matrix into a C×D matrix;

[0028] Step 22: Every two columns of the C×D matrix are combined to generate a C×E matrix H; where A = C*D and D = 2E.

[0029] Furthermore, the process of using a 4D hyperchaotic model to perform subcarrier and symbol scrambling on the data in Step 3 is as follows:

[0030] Step 31: Use the chaotic sequences generated by the state variables Y and W in the 4D hyperchaotic model to scramble the subcarriers and symbol points of the data to be transmitted respectively, generating chaotic sequences X(2) and X(4), where the subcarriers correspond to each column of matrix H, and the symbols correspond to each element of matrix H;

[0031] Step 32: Sort the chaotic sequences X(2) and X(4) in ascending order respectively, and then take the reciprocals to form two reciprocal matrices;

[0032] Step 33: Multiply these two reciprocal matrices by the initial matrix H to generate two scrambled matrices X 2 、X 4 , which can be represented by the following formulas respectively:

[0033]

[0034] Step 34: The two scrambled matrices X 2 、X 4 are respectively used to scramble the subcarriers and symbols. In these two matrices, each row and each column contains only one 1, and all other elements are 0;

[0035] Step 35: Then, extract the positions of 1 from the scrambled matrices X 2 、X 4 generated by Y and W respectively to generate two scrambled sequences M and N, where the scrambled sequence M is a 1×E matrix, and the scrambled sequence N is a 1×C matrix;

[0036] Step 6: Then, perform column transformation on the C×E matrix H according to each column element of the scrambled sequence M, that is, rearrange according to the elements in the scrambled sequence; Similarly, after transposing the scrambled sequence N, perform row transformation on the matrix H; complete the scrambling of the subcarriers and symbols, and finally obtain a C×E matrix P.

[0037] Furthermore, the process of modulating the binary key using the multi-constellation index joint modulation method in Step 4 is as follows:

[0038] Step 41: Convert the key initial values (X0, Y0, Z0, W0) of the chaotic model into binary. There are four key initial values in total, and each initial value consists of 8-bit decimal fractions. After converting the key initial values into binary, there are 128 bits in total;

[0039] Step 42: Repeat the key C times to obtain a C×F key index matrix. Each element of the matrix represents an index bit, that is, [0, 1], and each index bit has two bits; there are four types of index bits, namely [0, 0], [0, 1], [1, 0], [1, 1];

[0040] Step 43: The constellation index mapping adopts two mapping rules A and B. Among them, the index bit [0,0] corresponds to the index position [1,2], representing the constellation point mapping position information of mapping rule A. [1,2] means that the constellation points of A can only be mapped to the first and second positions, that is , and the remaining positions map the constellation points of B. The superscripts (1) and (2) represent the first and second constellation points of A or B; and so on, there are four combination methods;

[0041] Step 44: The original data undergoes the above processing process to obtain the matrix P of C×E. Since QPSK mapping is adopted, each element of the matrix P represents two bits; after the matrix P passes through the mapping selector, it is correspondingly matched and jointly modulated with the key index matrix generated by the key transformation, and finally the jointly modulated constellation points are obtained.

[0042] Furthermore, the transmission process of the transmitted signal through the OFDM system in step 5 is as follows

[0043] Step 51: The jointly modulated constellation points are represented in the way of adding the real part and the imaginary part.

[0044] Step 52: First, perform the inverse Fourier transform on the complex constellation points to convert the frequency-domain signal into a time-domain signal, and the matrix size becomes C×G;

[0045] Step 53: Secondly, add a cyclic prefix and a suffix to the front and back of this matrix respectively to reduce the inter-symbol interference. The length of the cyclic prefix is selected as J, and the length of the suffix is C. At this time, the matrix becomes a time-domain signal of C×K. After the time-domain signal is transmitted through the optical fiber channel, the cyclic prefix and the suffix are removed;

[0046] Step 54: Then, it is converted into a frequency-domain signal through the Fourier transform to restore the effective data matrix of C×E and obtain the constellation points of the received signal.

[0047] Furthermore, the process of decrypting and demodulating the received signal in step 6 is as follows

[0048] Step 61: Divide the received effective data matrix of C×E into C×F groups. Each group hides the index bit information of two bits, that is, two-bit information of the key;

[0049] Step 62: Extract the hidden index bits of each group, and then match the combination method of the key to obtain C extracted keys;

[0050] Step 63: Select the index bit with the most occurrences as the correct key information, and finally extract the absolutely correct key;

[0051] Step 64: Since the key is repeated up to C times, even in the case of a very low signal-to-noise ratio, the bit error rate of the key can still be guaranteed to be zero; substitute the correct key into the 4D hyperchaotic model, and use the four chaotic sequences generated by it to decrypt the original data to obtain a 1×A original binary data stream;

[0052] Step 65: On the premise of ensuring that the finally extracted key is completely correct, perform QPSK demapping on the received C×E matrix, and then substitute the key into the 4D hyperchaotic model to generate the same chaotic sequence. Based on the chaotic sequence, the symbol recovery and subcarrier recovery of the encrypted data can be realized in sequence, and then the data is converted from parallel to serial to obtain a binary bit stream. Finally, bitwise XOR is performed on the binary bit stream to realize the final decryption of the data and recover the original data.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] 1. A high-security joint modulation method for information transmission based on multi-constellation indexing according to the present invention performs multi-dimensional perturbation on the bits, subcarriers, and symbols of the initial signal through a four-dimensional chaotic model, adopts key matching joint modulation based on multi-constellation indexing, represents the key with the position information of the constellation points, and then realizes the synchronous high-security and high-performance transmission of the key-adjacent signal by matching the position of the constellation points of the two mapping rules.

[0055] 2. A high-security joint modulation method for information transmission based on multi-constellation indexing according to the present invention, during the process of the key accompanying the signal transmission, neither affects the transmission performance of the valid information nor causes redundant data processing, ensuring the high-performance transmission of the key itself.

[0056] 3. A high-security joint modulation method for information transmission based on multi-constellation indexing according to the present invention, at the legal receiving end, accurately extracts the key through the position information of the constellation points to decrypt the data. When the signal-to-noise ratio is greater than 9, the bit error rate at the legal receiving end is lower than the decision threshold. At the same time, as the signal-to-noise ratio increases, the bit error rate gradually decreases, achieving a good transmission effect and having high information security. Description of the Drawings

[0057] Figure 1 is a flowchart of the high-security joint modulation method for information transmission based on multi-constellation indexing according to the present invention;

[0058] Figure 2 is a phase trajectory diagram of the 4D hyperchaotic model in the present invention;

[0059] Figure 3 is a flowchart of the multi-constellation indexing joint modulation method in the present invention;

[0060] Figure 4It is the constellation diagram of the received signal in the present invention;

[0061] Figure 5 It is the curve graph of the key quality bit error rate of the present invention;

[0062] Figure 6 It is the curve graph of the bit error rate between the illegal receiver and the legitimate receiver of the present invention. Detailed implementation manners

[0063] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0064] The purpose of the present invention is to provide a high-security joint modulation method for information transmission based on multi-constellation indexing in view of the defects of the prior art.

[0065] Embodiment 1

[0066] A high-security joint modulation method for information transmission based on multi-constellation indexing, as shown in reference to Figure 1 shown, includes the following steps,

[0067] Step 1: At the sending end, use a 4D hyperchaotic model to perform bitwise exclusive OR encryption on the randomly generated A-bit binary bit stream original data to obtain the binary bit stream T after exclusive OR scrambling;

[0068] The 4D hyperchaotic model can be expressed as:

[0069]

[0070]

[0071] where X, Y, Z, W are state variables, and a, b, c, d, k are system parameters; when a = 10, b = 100, c = 10,

[0072] Figure 2 d = 0.27, k = 100, this system has two positive Lyapunov exponents, which proves that this system is a hyperchaotic system. Figure 2 shown. FromFigure 2 It can be seen that the value ranges of the four chaotic sequences of the 4D hyperchaotic model are (-85, 81), (-25, 23), (-26, 21), and (-31, 32) respectively.

[0073] The dynamic behavior of the 4D hyperchaotic model is more complex, and this complexity increases the unpredictability and sensitivity of the system. The chaotic system provides more parameters and variables, and can generate complex and difficult-to-break encryption keys, thereby improving the security of data transmission. Due to the high complexity, non-periodicity, and pseudo-random characteristics of the output of the 4D hyperchaotic model, it can be effectively used in fields such as information encryption, noise removal, and image restoration.

[0074] Step 2: Perform serial-to-parallel conversion on the encrypted data to generate a matrix H of C×E;

[0075] Step 3: Perform subcarrier and symbol scrambling on the converted data to generate a matrix P of C×E, completing the chaotic encryption process;

[0076] Step 4: Subsequently, modulate the key that has been converted into binary using the multi-constellation index joint modulation method to construct a key index matrix, and use the index matrix to combine two QPSK modulation formats to obtain the transmitted signal;

[0077] Step 5: The transmitted signal is transmitted through the OFDM system;

[0078] Step 6: At the receiving end, extract the correct key through the constellation point position information of QPSK modulation, and use the extracted key to decrypt and demodulate the received signal to obtain the original data.

[0079] The present invention performs multi-dimensional perturbation on the bits, subcarriers, and symbols of the initial signal through the 4D hyperchaotic model, performs chaotic encryption based on the OFDM signal, improves the security of information transmission, and adopts key matching joint modulation based on multi-constellation index to realize the transmission of the key along with the signal. At the legitimate receiving end, due to the known key hiding method, the initial signal can still be correctly restored even in the case of very poor signal-to-noise ratio. Compared with the traditional key transmission method based on noise masking, which will affect the transmission quality of the signal itself, since the present invention uses the position information of the constellation points to represent the key, the key does not affect the transmission performance of the signal itself during the transmission process; compared with the method of transmitting the key hidden in the frame header, the key transmission method adopted by the present invention does not cause redundant data processing, thereby enabling high-security and high-performance transmission of the key along with the signal.

[0080] Embodiment 2

[0081] A high - security joint modulation method for information transmission based on multi - constellation indexing. In the first embodiment, in step 1, the bit - exclusive - OR encryption process of the original data is as follows: Using a 4D hyper - chaotic model to process an A - bit original binary bit - stream to obtain:

[0082]

[0083] where X(1) and X(3) represent chaotic sequences, each having A / 2 elements, which are generated by the state variables X and Z in the chaotic model respectively; X 1 、X 3 represent the processed sequences.

[0084] X is a binary exclusive - OR bit - stream with the same size as the original binary bit - stream , that is, X is also A bits and directly participates in the exclusive - OR scrambling;

[0085] T represents the finally obtained exclusive - OR scrambled binary bit - stream, and T is determined by the parity of the fourth digit after the decimal point of the elements in the chaotic sequences X(1) and X(3), that is, odd is 1 and even is 0;

[0086] floor(-) is the floor function, and mod(-) is the remainder function.

[0087] In the first embodiment, the process of serial - to - parallel conversion of the data in step 2 is as follows:

[0088] Step 21: Convert the binary data stream after bit - exclusive - OR scrambling from the initial 1×A matrix to a C×D matrix;

[0089] Step 22: Combine every two columns of the C×D matrix to generate a C×E matrix H; thus facilitating subsequent sub - carrier scrambling, where A = C*D and D = 2E. Specifically, in this embodiment, A = 20480, C = 40, D = 512, and E = 256.

[0090] In the first embodiment, the process of using the 4D hyper - chaotic model to scramble sub - carriers and symbols of the data in step 3 is as follows:

[0091] Step 31: First, use the chaotic sequences generated by the state variables Y and W in the 4D hyper - chaotic model to scramble the sub - carriers and symbol points of the data to be transmitted respectively, generating chaotic sequences X(2) and X(4), where the sub - carriers correspond to each column of the matrix H and the symbol points correspond to each element of the matrix H;

[0092] Step 32: Next, sort the chaotic sequences X(2) and X(4) in ascending order respectively, and then take the reciprocal to form two reciprocal matrices;

[0093] Step 33: Then, multiply these two reciprocal matrices by the initial matrix H to generate two scrambled matrices X 2 and X 4 , which can be represented by the following formulas respectively:

[0094]

[0095] Step 34: Next, the two scrambled matrices X 2 and X 4 are used to scramble the subcarriers and symbols respectively. In these two matrices, each row and each column contains only one 1, and all other elements are 0;

[0096] Step 35: Then, extract the positions of 1s from the scrambled matrices X 2 and X 4 generated from Y and W to generate two scrambled sequences M and N respectively. Among them, the scrambled sequence M is a 1×E matrix, and the scrambled sequence N is a 1×C matrix;

[0097] Step 36: Then, perform column transformation on the C×E matrix H according to each column element of the scrambled sequence M, that is, rearrange according to the elements in the scrambled sequence; similarly, after transposing the scrambled sequence N, perform row transformation on the matrix H; complete the scrambling of the subcarriers and symbols, and finally obtain a 40×256 matrix P.

[0098] Example Three

[0099] Referring to Figure 3 shown, for a high-security joint modulation method based on multi-constellation indexing for information transmission, the process of modulating a binary key using the multi-constellation indexing joint modulation method in step 4 of Example 1 is as follows:

[0100] Step 41: First, convert the key initial values (X0, Y0, Z0, W0) of the chaotic model into binary. There are four key initial values in total, and each initial value consists of 8-bit decimal fractions. After converting the key initial values into binary, there are 128 bits in total.

[0101] Step 42: Then, repeat the key 40 times to obtain a 40×F key index matrix, where F = 64. Each element of the matrix represents an index bit, that is, [0, 1], and each index bit has two bits; there are four types of index bits, namely [0, 0], [0, 1], [1, 0], and [1, 1].

[0102] The constellation index mapping adopts two mapping rules A and B. Among them, the index bit [0, 0] corresponds to the index position [1, 2], representing the constellation point mapping position information of mapping rule A, as shown in Table 1. [1, 2] means that the constellation points of A can only be mapped to the first and second positions, that is , the remaining positions map the constellation points of B. The superscripts (1) and (2) represent the first and second constellation points of A or B; and so on, there are four combination methods in total.

[0103] Table 1 Constellation Index Mapping Rules

[0104] Index bit Index position Constellation point distribution [0,0] [1,2] #timg# [0,1] [2,3] #timg# [1,0] [3,4] #timg# [1,1] [1,4] #timg#

[0105] Step 44: The original data undergoes the above processing process to obtain a 40×256 matrix P. Since QPSK mapping is adopted, each element of matrix P represents two bits; after matrix P passes through the mapping selector, it is corresponding and matched with the key index matrix generated by key transformation for joint modulation, and finally the jointly modulated constellation points are obtained.

[0106] In step 5, the transmission process of the transmitted signal through the OFDM system is as follows:

[0107] Step 51: The jointly modulated constellation points are represented in the way of adding the real part and the imaginary part.

[0108] Step 52: First, perform the inverse Fourier transform on the complex constellation points to convert the frequency-domain signal into a time-domain signal, and the matrix size becomes 40×G, where G = 1024 in this embodiment;

[0109] Step 53: Secondly, add a cyclic prefix and a suffix to the front and back of this matrix respectively to reduce the inter-symbol interference. Select the cyclic prefix length as J, J = 128 in this embodiment, and the suffix length is 40. At this time, the matrix becomes a time-domain signal of 40×K, K = 1320 in this embodiment. After the time-domain signal is transmitted through the optical fiber channel, the cyclic prefix and the suffix are removed;

[0110] Step 54: Then, it is converted back to a frequency-domain signal through Fourier transform to restore the 40×256 effective data matrix, and the constellation points of the received signal are obtained. Its constellation diagram is as Figure 4 shown.

[0111] The multi-constellation index joint modulation method adopts two constellation mapping rules, uses the value of the key as the index bit. This index bit has four types, corresponding to four different constellation mapping position information. By freely controlling the mapping positions of the two constellation points through the index bit, the joint modulation of the key matching constellation point positions is realized. At the receiving end, we accurately extract the key relying on the position information of the constellation points, and successfully realize the transmission of the key along with the signal. By using the position information of the constellation points to represent the key, it does not affect the transmission performance of the signal itself during the transmission process.

[0112] Example 4

[0113] A high-security joint modulation method for information transmission based on multi-constellation indexing. In Step 6 of Embodiment 1, the process of decrypting and demodulating the received signal is as follows:

[0114] Step 61: Divide the received 40×256 effective data matrix into 40×64 groups. Each group hides two-bit index bit information, that is, two-bit information of the key.

[0115] Step 62: Extract the hidden index bits of each group, and then match the combination mode of the key to obtain 40 extracted keys.

[0116] Step 63: Select the index bit that appears the most times as the correct key information, and finally extract the absolutely correct key.

[0117] Step 64: Since the key is repeated up to 40 times, even in the case of a very low signal-to-noise ratio, the bit error rate of the key can still be guaranteed to be zero. Substitute the correct key into the 4D hyperchaotic model, and use the four chaotic sequences generated by it to decrypt the original data to obtain a 1×20480 original binary data stream.

[0118] For the high-security key transmission method, the transmission quality of the key is extremely important. Since the chaotic system itself is very sensitive to the key initial value, even a slight change in the initial value will result in completely different chaotic sequences, thus making it impossible to correctly decrypt the signal.

[0119] In the present invention, to ensure the absolute correctness of key transmission, the key is repeated 40 times, which is equivalent to circularly sampling the key 40 times. After extracting the key, information comparison is also performed on the key, and the one that appears the most times among the 40 groups of keys is selected as the final correct key, thereby ensuring error-free transmission of the key.

[0120] Refer to Figure 5 As shown, it can be seen from the figure that when the signal-to-noise ratio is 6, the bit error rate of the key is already zero, indicating that error-free transmission of the key can still be achieved even in the case of a very low signal-to-noise ratio.

[0121] Step 65: On the premise of ensuring that the finally extracted key is completely correct, perform QPSK demapping on the received 40×256 matrix. Then substitute the key into the 4D hyperchaotic model to generate the same chaotic sequence. Based on the chaotic sequence, symbol recovery and subcarrier recovery of the encrypted data can be achieved in sequence, and then the data is converted from parallel to serial to obtain a binary bit stream. Finally, bitwise XOR is performed on the binary bit stream to achieve the final decryption of the data and restore the original data.

[0122] Refer to Figure 6As shown, the comparison diagram of the bit error rate curves of the legal receiver and the illegal receiver after restoring the original data is respectively shown. The yellow dotted line in the figure represents 3.8×10 -3 the hard decision forward error correction threshold (FEC). It can be seen that when the signal-to-noise ratio is greater than 9, the bit error rate of the legal receiver is lower than the decision threshold. At the same time, as the signal-to-noise ratio increases, the bit error rate gradually decreases, achieving a good transmission effect. However, since the illegal receiver cannot obtain the correct key information, it cannot decrypt the encrypted signal correctly. Thus, it can be seen that the method proposed by the present invention has high information security and good information transmission performance.

[0123] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-security joint modulation method for information transmission based on multiple constellation indexes, characterized in that: The following steps are included: Step 1: At the sending end, the 4D hyperchaotic model is used to perform bit XOR encryption on the randomly generated A-bit binary bit stream original data to obtain the XOR-scrambled binary bit stream T; The 4D hyperchaotic model is expressed as: Among them, X, Y, Z, W are state variables, a, b, c, d, k are system parameters; Step 2: Perform serial-to-parallel conversion on the encrypted data to generate a C×E matrix H; Step 3: Scramble the subcarriers and symbols of the converted data to generate a C×E matrix P, completing the chaotic encryption process; Step 4: The key converted into binary is then modulated using a multi-constellation index joint modulation method to construct a key index matrix, and the index matrix is ​​combined with two QPSK modulation formats to obtain a transmission signal; Step 5: Send the signal for transmission through the OFDM system; Step 6: At the receiving end, the correct key is extracted through the constellation point position information modulated by QPSK, and the received signal is decrypted and demodulated using the extracted key to obtain the original data; The bit XOR encryption method of the original data in step 1 is to use the 4D hyperchaotic model to process the original binary bit stream T' of A bits, and we can get: The chaotic sequences X(1) and X(3) each have A / 2 elements, which are generated by the state variables X and Z in the chaotic model respectively; X is a binary XOR bit stream of the same size as the original binary bit stream T', that is, X is also A bits and directly participates in the XOR scrambling of T'; T is the final binary bit stream after XOR scrambling, where T is determined by the parity of the fourth decimal place of the elements in the chaotic sequences X(1) and X(3), that is, odd numbers are 1 and even numbers are 0; floor(-) is the function of rounding down to an integer, and mod(-) is the remainder function; The process of modulating the binary key using the multi-constellation index joint modulation method in step 4 is as follows: Step 41: Convert the initial key value (X0, Y0, Z0, W0) of the chaotic model into binary. The key has four initial values, each of which consists of 8 decimal digits. After the initial key value is converted into binary, it has 128 bits in total. Step 42: Repeat the key C times to obtain a C×F key index matrix, where each element of the matrix represents an index bit, i.e., [0,1], and each index bit has two bits. There are four types of index bits, i.e., [0,0], [0,1], [1,0], [1,1]; Step 43: The constellation index mapping adopts two mapping rules A and B, where the index bit [0,0] corresponds to the index position [1,2], representing the constellation point mapping position information of mapping rule A, and [1,2] indicates that the constellation point of A can only be mapped at the first and second positions, that is, The remaining positions are mapped to the constellation points of B. The superscripts (1) and (2) represent the first and second constellation points of A or B. And so on. There are four combinations in total. Step 44: The original data is processed through the above process to obtain a C×E matrix P. Since QPSK mapping is adopted, each element of the matrix P represents two bits. After passing through the mapping selector, the matrix P is matched with the key index matrix generated by the key transformation for joint modulation, and finally the constellation points of the joint modulation are obtained.

2. The high-security joint modulation method for information transmission based on multi-constellation indexes according to claim 1, characterized in that: The process of serial-to-parallel conversion of the data in step 2 is as follows: Step 21: transform the binary data stream after bit XOR scrambling from the original 1×A matrix into a C×D matrix; Step 22: Merge every two columns of the C×D matrix to generate a C×E matrix H; Where A=C*D, D=2E.

3. The high-security joint modulation method for information transmission based on multi-constellation indexes according to claim 1, characterized in that: The process of using the 4D hyperchaotic model to scramble the subcarriers and symbols of the data in step 3 is as follows: Step 31: Use the chaotic sequences generated by the state variables Y and W in the 4D hyperchaotic model to scramble the subcarriers and symbol points of the data to be transmitted, respectively, to generate chaotic sequences X(2) and X(4), where the subcarrier corresponds to each column of the matrix H, and the symbol corresponds to each element of the matrix H; Step 32: Sort the chaotic sequences X(2) and X(4) in ascending order respectively, and then take the reciprocals to form two reciprocal matrices; Step 33: Multiply the two reciprocal matrices with the initial matrix H to generate two scrambled matrices X2 and X4, which can be expressed by the following formulas: Step 34: Two scrambling matrices X2 and X4 are used to scramble the subcarriers and symbols respectively. In these two matrices, each row and column contains only one 1, and all other elements are 0; Step 35: Next, extract the position of 1 from the scrambled matrices X2 and X4 generated by Y and W, and generate two scrambled sequences M and N respectively, where the scrambled sequence M is a 1×E matrix and the scrambled sequence N is a 1×C matrix; Step 6: Then, the C×E matrix H is transformed in columns according to each column element of the scrambled sequence M, that is, the elements in the scrambled sequence are rearranged; similarly, after transposing the scrambled sequence N, the matrix H is transformed in rows; the scrambling of the subcarriers and symbols is completed, and finally a C×E matrix P is obtained.

4. The high-security joint modulation method for information transmission based on multi-constellation indexes according to claim 1, characterized in that: The transmission process of sending the signal through the OFDM system in step 5 is: Step 51: The constellation points after joint modulation are expressed by adding the real part to the imaginary part. Step 52: First, perform inverse Fourier transform on the complex constellation points to convert the frequency domain signal into a time domain signal, and the matrix size becomes C×G; Step 53: Secondly, add a cyclic prefix and a suffix before and after the matrix to reduce the crosstalk between symbol points. The cyclic prefix length is selected as J and the suffix length is selected as C. At this time, the matrix becomes a C×K time domain signal. After the time domain signal is transmitted through the optical fiber channel, the cyclic prefix and the suffix are removed. Step 54: Convert it into a frequency domain signal through Fourier transform, restore the C×E effective data matrix, and obtain the constellation points of the received signal.

5. The high-security joint modulation method for information transmission based on multi-constellation indexes according to claim 1, characterized in that: The process of receiving the signal for decryption and demodulation in step 6 is as follows: Step 61: Divide the received C×E valid data matrix into C×F groups, each group hiding two bits of index bit information, that is, two bits of key information; Step 62: Extract the hidden index bits of each group, and then match the key combination to obtain C extraction keys; Step 63: Select the index bit with the most occurrences as the correct key information, and finally extract the absolutely correct key; Step 64: Since the key is repeated C times, the bit error rate of the key can be guaranteed to be zero even when the signal-to-noise ratio is very low. Substitute the correct key into the 4D hyperchaotic model and use the four chaotic sequences generated by it to decrypt the original data to obtain the original binary data stream of 1×A. Step 65: Under the premise of ensuring that the final key extracted is completely correct, perform QPSK demapping on the received C×E matrix, and then substitute the key into the 4D hyperchaotic model to generate the same chaotic sequence. Based on the chaotic sequence, the symbol recovery and subcarrier recovery of the encrypted data can be realized in turn, and then the data is converted from parallel to serial to obtain a binary bit stream. Finally, the binary bit stream is bit-XORed to achieve the final decryption of the data and restore the original data.

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