Signal transmission method based on three-dimensional constellation step coding

Abstract

The invention discloses a signal transmission method based on three-dimensional constellation step coding, and the method comprises the steps: carrying out the XOR encryption and sub-block scrambling of initial signal data, and generating a 64QAM (Quadrature Amplitude Modulation) signal; after up-sampling, actively introducing an error sequence to generate a state base; signal step coding is carried out through a quasi-quantum noise flow method, and information hiding of 64QAM signals is achieved; the ultra-high-order signal is scrambled and encrypted and then enters an optical fiber channel after passing through an OFDM system, and a received signal is obtained; and demodulating the state base, regenerating a scrambling sequence, performing chaos scrambling recovery after recovery decryption, reducing the order of the signal to a 64QAM signal in a three-dimensional space, and performing XOR recovery to obtain initial data. According to the invention, 64QAM is designed in a three-dimensional space, the secret key is used as a state base to realize accompanying transmission, the safety performance of the signal is further improved in combination with a chaotic system, and finally, high-performance and high-safety signal transmission is realized.

Description

Technical Field

[0001] This invention belongs to the field of mobile communications and relates to optical signal data transmission technology, specifically to a signal transmission method based on three-dimensional constellation step coding. Background Technology

[0002] The continuous innovation of mobile communication network technology, along with the development of 5G communication, cloud computing platforms, and smart IoT systems, has placed higher demands on optical transmission. Against the backdrop of exponential growth in user access and a surge in data transmission volume, optical fiber communication, with its wideband transmission, long-distance coverage, and strong anti-interference characteristics, has become the core transmission medium for access networks. Among them, Passive Optical Network (PON) technology, due to its advantages of high bandwidth, low loss, and low cost, has gradually evolved from Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM) to the current mainstream Orthogonal Frequency Division Multiplexing (OFDM) architecture, becoming an important development direction for next-generation access networks.

[0003] However, with the further development of digitalization, signal security has become an issue that cannot be ignored. In terms of communication security, the downlink broadcast mechanism of traditional PON systems has inherent security flaws. Furthermore, with the breakthroughs in quantum computing technology, information transmission often faces eavesdropping attacks and brute-force attacks. Existing encryption systems mainly focus on the network protocol layer and the physical layer. Protocol layer encryption relies on complex key management systems, which cannot be efficiently managed in the face of increasing data volumes. Chaotic encryption technology in physical layer encryption schemes has attracted much attention due to its operation in the digital domain, lack of additional redundancy, and high sensitivity to initial values. However, existing implementations mostly focus on offline processing at both the transmitting and receiving ends, failing to effectively integrate channel characteristics. Quantum Noise Stream Cipher (QNSC) is a novel physical layer security scheme that achieves secure signal processing by using noise in the channel to mask the decision level through multiple ground state transitions from an initial low-order signal to a higher-order signal. However, because the state base is generated using a linear shift register, once the header data is leaked, the entire state base information will be exposed to unauthorized receivers, posing a risk of brute-force attacks. The above scheme boasts extremely high security, but it overlooks the fact that the entire encryption scheme relies on both the sending and receiving ends knowing the key. However, in reality, the sending and receiving ends do not directly know the key, and once the key is leaked, the above scheme cannot be adjusted in time, leading to continuous losses. Current key transmission schemes also exist, such as using polarization states or phase to transmit the encoded key, but these require additional components and computational overhead, making widespread practical application difficult. Therefore, how to securely and efficiently achieve masked key transmission has become a key research direction for scholars. Summary of the Invention

[0004] Purpose of the invention: Most current communication transmission schemes are carried out in traditional two-dimensional space. Compared with three-dimensional space, they often have higher average transmission power at the same minimum Euclidean distance, resulting in poor transmission performance. At the same time, current physical layer security schemes are almost all based on the knowledge of the keys at both ends, ignoring the secure transmission of keys. Moreover, once the key information is leaked, it will cause continuous losses. Existing schemes cannot flexibly deal with this situation. Therefore, this invention provides a signal transmission method based on three-dimensional constellation step coding.

[0005] Technical solution: To achieve the above objectives, this invention provides a signal transmission method based on three-dimensional constellation step coding, comprising the following steps:

[0006] S1: Perform XOR encryption on the initial signal data, then perform sub-block scrambling on the subcarriers and symbol points of the signal, and then perform constellation mapping to generate a 64QAM signal;

[0007] S2: After upsampling the initial key, an error sequence is actively introduced, and the state base is generated by mixing chaotic bits with the key;

[0008] S3: Based on the 64QAM signal and state basis, the signal is encoden using a quantum-like noise flow method, which upgrades the 64QAM signal to a super-high-order 32768QAM signal, thereby achieving information hiding of the 64QAM signal;

[0009] S4: After the ultra-high order signal is scrambled and encrypted, it is passed through the OFDM system and then enters the optical fiber channel, where the receiving end receives the signal.

[0010] S5: At the receiving end, the state base is first demodulated, that is, the key of the chaotic system is recovered by demodulation. Then, the original key is brought into the chaotic system to regenerate the scrambled sequence. After decryption through quantum noise stream recovery, chaotic scrambling recovery is performed. Then, the signal is reduced to a 64QAM signal in three-dimensional space through constellation demapping. Finally, the initial data is obtained by XOR recovery.

[0011] Furthermore, in step S1, the signal is chaotically encrypted using a pre-designed six-dimensional hyperchaotic system. The model of the six-dimensional hyperchaotic system is expressed as follows:

[0012] (1)

[0013] Where X, Y, Z, U, V, W are six-dimensional state variables, and a, b, c, d, k, h, l are six-dimensional system parameters.

[0014] Furthermore, in step S1, the initial signal data is a randomly generated binary data stream. The initial data is bit-XORed using a chaotic sequence X generated by a six-dimensional hyperchaotic system. The generation operation of the chaotic sequence X is as follows:

[0015] (2)

[0016] Where mod(-) is the remainder function, floor(-) is the floor function, and R1 is the binarized sequence obtained by taking the fourth decimal place of the chaotic sequence and XORing it with the randomly generated data.

[0017] Furthermore, in step S1, the chaotic sequences generated using Y and Z from the chaotic sequences are used to scramble the subcarriers and symbol points of the signal into sub-blocks, respectively. The specific operations are as follows:

[0018] (3)

[0019] Where mod(-) is the remainder function and sort(-) is the ascending sort function;

[0020] First, sort the chaotic sequences Z and U in ascending order and then count their reciprocals to generate matrices. Then multiply these matrices with the original matrices to generate a scrambled matrix with the orders of the number of subcarriers and the number of symbols, respectively. Each row and column of the matrix contains a 1, and the remaining elements are all marked as 0. Extract the positions of the 1s from the matrices generated by Z and U to generate two scrambled sequences.

[0021] Furthermore, in step S2, the erroneous sequence uses noise bits, which are given by chaotic sequences U, V, and W. The specific operation is as follows:

[0022] (4)

[0023] (5)

[0024] In formula (4), downsampling(-) is the downsampling function; the chaotic sequences U, V, and W generated in formula (1) are sampled every 50 bits to ensure the randomness of the chaotic sequences; in formula (5), mod(-) is the remainder function and floor(-) is the floor function. This process can generate random numbers from 0 to 9 from the downsampled chaotic sequences, and then make a decision on the obtained random numbers from 0 to 9 to generate random 0 and 1 noise bits. The chaotic bits generated in this way have random chaotic properties, which can ensure the uniform distribution of the state basis while ensuring the key security performance. Each set of chaotic sequences generates 20480 bits.

[0025] Further, step S3 includes:

[0026] By combining the 64QAM data with the state base using high and low bits, the constellation order transition is achieved. Specifically, the encrypted X, Y, and Z data are composed of (X, Y, Z). Encrypted =(S X + B X S Y + B Y S Z + B Z The data is given by using 512 basic states (X, Y and Z are 3 bits each, corresponding to 8 basic states respectively) to encrypt 64QAM data, resulting in 32768 encryption symbols ((4×8)×(4×8)×(4×8)=32×32×32), thus hiding the 64QAM information within it.

[0027] Furthermore, in step S4, for signal transmission, the row and column are subjected to two Inverse Fast Fourier Transform (IFFT) operations, and then the frequency domain signal is converted into a time domain signal. To reduce inter-symbol interference, a cyclic prefix and suffix are added before and after the symbols. Then, the modulated parallel time domain signal is converted from parallel to serial to a serial signal and enters the optical fiber channel. At the receiving end, the reverse operation is performed. After serial-to-parallel conversion, removal of cyclic prefixes and suffixes, and Fourier transform, the received signal to be decrypted is obtained.

[0028] Furthermore, in step S5, the correct key for transmission is obtained using the decision state base. Since the key is cyclically sampled, after the key information is extracted, it is compared, and the information that appears most frequently in each sampling number is taken as the final key, which can effectively ensure the accuracy of the key.

[0029] Furthermore, in step S5:

[0030] For legitimate receivers, decoding is aided by known state base information; points where all three state bases are identical are locked for judgment. In three-dimensional space, due to the periodic arrangement of state bases, there will only be 64 points where all three state bases are identical. In this case, the least Euclidean distance is used to make a judgment on the constellation points that need to be judged.

[0031] For illegal receivers, it is difficult to know the correct state of the signal due to noise. The only option is to use brute-force demodulation to calculate the Euclidean distance from each symbol to 32,768 locations, and the smallest distance is the correct location of the symbol. This approach is undoubtedly extremely difficult and has a very low accuracy.

[0032] This invention designs a 64QAM constellation diagram in three-dimensional space, offering superior transmission performance compared to traditional two-dimensional 64QAM. Furthermore, for signal security, it combines chaotic encryption technology with a quantum-like noise flow scheme to encrypt the signal. A six-dimensional hyperchaotic system is employed to perform multi-dimensional perturbations on data bits, subcarriers, symbol points, and constellation order transitions, while simultaneously masking the key information within the state base for accompanying transmission. To ensure the accuracy and security of the key information, this invention encodes the key bits, upsamples them, and then actively introduces noise bits for encryption, ultimately achieving ultra-high-order signal transmission from 64QAM to 32768QAM. For legitimate receivers, knowing the encryption method, correct decryption and demodulation are possible, while illegitimate receivers, unaware of the modulation order and encryption method, struggle to demodulate or brute-force crack the encryption.

[0033] This invention utilizes a constellation diagram in three-dimensional space for signal transmission, improving signal transmission performance. Simultaneously, a quantum-like noise flow method is employed to encode transitions in low-order signals while ensuring signal security. A six-dimensional hyperchaotic system is used to perform multi-dimensional perturbations on bits, subcarriers, symbol points, and the constellation. To achieve accompanying key transmission, the key is upsampled and partially noise-introduced, then transmitted as part of the state basis. The state basis is used to increase the constellation order, and noise in the channel is used to mask the decision level, ultimately completing the 3D-32768QAM signal transmission.

[0034] Beneficial Effects: Compared with existing technologies, this invention designs the constellation diagram in three-dimensional space, which reduces the average signal power while maintaining the same minimum Euclidean distance, thereby improving transmission performance. Simultaneously, it employs a state-based masking key to achieve accompanying key transmission, enabling effective and timely responses to security risks. Furthermore, to ensure signal security, this scheme uses a quantum-like noise flow method to implement step-by-step coding of the original signal, effectively utilizing channel characteristics to mask the decision level with noise. Combining this with a chaotic system further enhances signal security, ultimately achieving high-performance and highly secure signal transmission. Attached Figure Description

[0035] Figure 1 This is a flowchart of the method of the present invention;

[0036] Figure 2 This is a schematic diagram of key transformation;

[0037] Figure 3 A schematic diagram illustrating the principle of transitioning to a 32768QAM signal;

[0038] Figure 4 A schematic diagram of constellation step transition using a quantum noise flow-like method;

[0039] Figure 5 This is a curve showing the change in bit error rate at the receiver as a function of signal-to-noise ratio. Detailed Implementation

[0040] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0041] Example 1:

[0042] like Figure 1 As shown, this embodiment provides a signal transmission method based on three-dimensional constellation step coding, including the following steps:

[0043] S1: Perform XOR encryption on the initial signal data, then perform sub-block scrambling on the subcarriers and symbol points of the signal, and then perform constellation mapping to generate a 64QAM signal;

[0044] S2: After upsampling the initial key, an error sequence is actively introduced, and the key-mixed chaotic bits are used to replace the shift register to generate the state base;

[0045] S3: Based on the 64QAM signal and state basis, the signal is encoden using a quantum-like noise flow method, which upgrades the 64QAM signal to a super-high-order 32768QAM signal, thereby achieving information hiding of the 64QAM signal;

[0046] S4: After the ultra-high order signal is scrambled and encrypted, it is passed through the OFDM system and then enters the optical fiber channel, where the receiving end receives the signal.

[0047] S5: At the receiving end, the state base is first demodulated, that is, the key of the chaotic system is recovered by demodulation. Then, the original key is brought into the chaotic system to regenerate the scrambled sequence. After decryption through quantum noise stream recovery, chaotic scrambling recovery is performed. Then, the signal is reduced to a 64QAM signal in three-dimensional space through constellation demapping. Finally, the initial data is obtained by XOR recovery.

[0048] To achieve the above process, this embodiment designs a six-dimensional hyperchaotic system to perform chaotic encryption on the signal. The model expression of the six-dimensional hyperchaotic system is as follows:

[0049] (1)

[0050] Where X, Y, Z, U, V, W are six-dimensional state variables, and a, b, c, d, k, h, l are six-dimensional system parameters. When a=10, b=8 / 3, c=28, d=2, k=8.4, h=1, l=1, the system is a hyperchaotic system. In this embodiment, the initial values ​​of X0, Y0, Z0, U0, V0, W0 of the chaotic model are set to (0.102030405060708; 0.012345678987654; 0.100568429753648; 0.100245726842315; 0.0548742159862284; 0.106654275365124).

[0051] In step S1, the initial signal data is a randomly generated binary data stream. In this embodiment, 61440 bits of information are generated. The initial data is bit-XORed using a chaotic sequence X generated by a six-dimensional hyperchaotic system. The generation operation of the chaotic sequence X is as follows:

[0052] (2)

[0053] Here, mod(-) is the remainder function, floor(-) is the floor function, and R1 is the binarized sequence obtained by taking the fourth decimal place of the chaotic sequence, which is then XORed with the randomly generated data. After this, sub-blocks are partitioned to obtain 40. A 256 matrix, where each element contains 6 bits, representing a 64QAM signal.

[0054] The chaotic sequences generated using Y and Z from the chaotic sequence are used to scramble the subcarriers and symbol points of the signal into sub-blocks, as follows:

[0055] (3)

[0056] Where mod(-) is the remainder function and sort(-) is the ascending sort function;

[0057] First, sort the chaotic sequences Z and U in ascending order and then count their reciprocals to generate matrices. Then multiply these matrices with the original matrices to generate a scrambled matrix with the orders of the number of subcarriers and the number of symbols, respectively. Each row and column of the matrix contains a 1, and the remaining elements are all marked as 0. Extract the positions of the 1s from the matrices generated by Z and U to generate two scrambled sequences.

[0058] Constellation Mapping: Due to the characteristics of 3D constellation encoding, each symbol point is given by its coordinates in 3D space, i.e., (x, y, z) represents its coordinates. That is, after mapping, it becomes 3D. 40 We split a 256 matrix into three dimensions, each with 40 elements. 256.

[0059] In step S2, key information is used instead of the state base in the traditional QNSC scheme to achieve key-accompanying transmission. First, the key is encoded; the key is the initial value of the chaotic system. Then, the six initial values ​​are converted from decimal to binary, with each digit converted to 4 binary bits, resulting in a total of 384 bits. To ensure key accuracy, this embodiment performs 80 upsampling operations. This is done to facilitate correct key demodulation at the receiving end. Next, to ensure the security of the key information, the error sequence uses noise bits, which are given by the chaotic sequences U, V, and W, as detailed below:

[0060] (4)

[0061] (5)

[0062] In formula (4), downsampling(-) is the downsampling function; the chaotic sequences U, V, and W generated in formula (1) are sampled every 50 bits to ensure the randomness of the chaotic sequences; in formula (5), mod(-) is the remainder function and floor(-) is the floor function. This process can generate random numbers from 0 to 9 from the downsampled chaotic sequences, and then make a decision on the obtained random numbers from 0 to 9 to generate random 0 and 1 noise bits. The chaotic bits generated in this way have random chaotic properties, which can ensure the uniform distribution of the state basis while ensuring the key security performance. Each set of chaotic sequences generates 20480 bits.

[0063] In this embodiment, as shown Figure 2 The diagram shows the introduction of noise bits into the keystream bits. See [link / reference]. Figure 2 The solution involves inserting two chaotic bits after each key information bit. Finally, to perform step-by-step encoding in three-dimensional space, the transformed key stream is divided into three parts, each containing 40 bits. A 256 matrix, where each element contains 3 bits as the state base and 1 bit of key information.

[0064] In step S3:

[0065] Quantum-like noise flow is used for step-by-step coding, such as Figure 3 As shown, the 64QAM data is combined with the state base in high and low bit combinations to achieve the transition of constellation order, that is, the encrypted X, Y and Z data are composed of (X, Y, Z). Encrypted =(S X + B X S Y+B Y S Z + B Z The following is given: 64QAM data is encrypted using 512 basic states (X, Y, and Z are each 3 bits, corresponding to 8 basic states), resulting in 32768 encryption symbols ((4×8)×(4×8)×(4×8) = 32 × 32×32), thus hiding the 64QAM information within it. In this embodiment, an extended constellation set is used to improve the system's security. The diffusion of quantum noise causes the intensity and phase of adjacent energy levels to completely overlap, thereby submerging the data information in noise.

[0066] like Figure 4 As shown, the previous steps have already separated the three data streams and the key. Figure 4 The diagram illustrates a 64QAM constellation, where 64QAM data is encrypted using 512 basic states (X, Y, and Z are each 3 bits). Each constellation point is distributed across these 512 basic states, resulting in a 32768QAM encrypted signal. This achieves a step-up encoding of the 64QAM signal, masking the signal into a higher-order constellation, and the decision level is covered by noise. For the data information, this embodiment uses the X-path as an example; every 8 symbols from right to left represent the same information as the corresponding constellation point in the original 64QAM signal. The state bases are periodically arranged in the symbols from 000 to 111, with each dimension's state base arranged periodically along the coordinate system shown in the diagram. After the step-up encoding is implemented, each constellation point is only masked within a region composed of a set of state bases, such as... Figure 4 The right half indicates that a constellation point in the original 64QAM will only move its position within the region contained in the cube, meaning that in each time slot, the 64QAM constellation can move in different state bases.

[0067] Step S4 concerns OFDM system transmission: In this embodiment, the three 40s after step-by-step coding are... 256 matrices merged into 120 256, of which 3 1 represents a constellation point. For the transmission scheme of the three-dimensional constellation diagram, the rows and columns are subjected to two Inverse Fast Fourier Transform (IFFT) operations, and then the frequency domain signal is converted into a time domain signal. To reduce inter-symbol interference, cyclic prefixes and suffixes are added before and after the symbols. Then, the modulated parallel time domain signal is converted from parallel to serial to a serial signal and enters the optical fiber channel. At the receiving end, the reverse operation is performed. After serial-to-parallel conversion, removal of cyclic prefixes and suffixes, and Fourier transform, the received signal that needs to be decrypted is obtained.

[0068] Step S5 concerns signal reception and demodulation: For a key-transmitted scheme, the key transmission performance is crucial. Key extraction errors introduced into a chaotic system will generate entirely different chaotic sequences, making demodulation impossible. This invention first utilizes a decision state basis to obtain the correct transmitted key. As explained in the above steps, this embodiment performs 80 cyclic samplings of the key. After extracting the key information, a comparison is made, and the information that appears most frequently in each of the 80 samplings is used as the final key. This effectively ensures the accuracy of the key.

[0069] State-based demodulation not only helps extract key information but also demodulates the original signal. For legitimate receivers, known state-based information aids decoding. Since the data information only relates to the higher-order bits, we can lock onto points where all three state bases are identical for decision-making. In three-dimensional space, due to the periodic arrangement of state bases, only 64 points will have identical state bases. In this case, we then perform minimum Euclidean distance judgment on the constellation points to be decided. This is equivalent to directly deciding 64QAM, and the Euclidean distance is greatly increased due to the order upgrade, becoming eight times the original. This decision method significantly improves decoding accuracy. However, for illegitimate receivers, under the influence of noise, it is difficult to know the correct signal state. They can only use brute-force demodulation, calculating the Euclidean distance from each symbol to 32,768 positions, with the smallest being the correct symbol position. This approach is undoubtedly extremely difficult and has very low accuracy.

[0070] Example 2:

[0071] To verify the effectiveness and efficacy of the method of the present invention, this embodiment obtains results through simulation experiments. Figure 5 The data shown is as follows: Figure 5 As shown, the horizontal axis represents the signal-to-noise ratio (SNR), and the vertical axis represents the bit error rate (BER) after demodulation. It can be observed that as the SNR increases, the BER at the legitimate receiver gradually decreases, which is consistent with theory. Figure 5 The document also includes a constellation diagram at a forward error correction threshold (FEC) of 3.8E-3, showing that the high-order 32768QAM effectively masks the decision level using channel noise. Furthermore, the BER of the illegitimate receiver remains around 0.5, due to the lack of knowledge of the signal's encryption method and modulation scheme. In summary, this invention can effectively achieve high-performance, high-security transmission of signals based on three-dimensional constellation step-order coded signals.

Claims

1. A signal transmission method based on three-dimensional constellation step-code, characterized in that, Includes the following steps: S1: Perform XOR encryption on the initial signal data, then perform sub-block scrambling on the subcarriers and symbol points of the signal, and then perform constellation mapping to generate a 64QAM signal; S2: After upsampling the initial key, an error sequence is actively introduced, and the state base is generated by mixing chaotic bits with the key; S3: Based on the 64QAM signal and state basis, the signal is encoden using a quantum-like noise flow method, which upgrades the 64QAM signal to a super-high-order 32768QAM signal, thereby achieving information hiding of the 64QAM signal; S4: After the ultra-high order signal is scrambled and encrypted, it is passed through the OFDM system and then enters the optical fiber channel, where the receiving end receives the signal. S5: At the receiving end, the state base is first demodulated, that is, the key of the chaotic system is recovered by demodulation. Then, the original key is brought into the chaotic system to regenerate the scrambled sequence. After decryption through quantum noise stream recovery, chaotic scrambling recovery is performed. Then, the signal is reduced to a 64QAM signal in three-dimensional space through constellation demapping. Finally, the initial data is obtained by XOR recovery.

2. The signal transmission method based on three-dimensional constellation step coding according to claim 1, characterized in that, In step S1, the signal is chaotically encrypted using a pre-designed six-dimensional hyperchaotic system. The model of the six-dimensional hyperchaotic system is expressed as follows: (1)； Where X, Y, Z, U, V, W are six-dimensional state variables, and a, b, c, d, k, h, l are six-dimensional system parameters.

3. The signal transmission method based on three-dimensional constellation step coding according to claim 2, characterized in that, In step S1, the initial signal data is a randomly generated binary data stream. The initial data is bit-XORed using a chaotic sequence X generated by a six-dimensional hyperchaotic system. The generation operation of the chaotic sequence X is as follows: (2)； Where mod(-) is the remainder function, floor(-) is the floor function, and R1 is the binarized sequence obtained by taking the fourth decimal place of the chaotic sequence and XORing it with the randomly generated data.

4. The signal transmission method based on three-dimensional constellation step coding according to claim 3, characterized in that, In step S1, the chaotic sequences generated using Y and Z from the chaotic sequence are used to scramble the subcarriers and symbol points of the signal into sub-blocks, respectively. The specific operation is as follows: (3)； Where mod(-) is the remainder function and sort(-) is the ascending sort function; First, sort the chaotic sequences Z and U in ascending order and then count their reciprocals to generate matrices. Then multiply these matrices with the original matrices to generate a scrambled matrix with the orders of the number of subcarriers and the number of symbols, respectively. Each row and column of the matrix contains a 1, and the remaining elements are all marked as 0. Extract the positions of the 1s from the matrices generated by Z and U to generate two scrambled sequences.

5. The signal transmission method based on three-dimensional constellation step coding according to claim 4, characterized in that, In step S2, the error sequence uses noise bits, which are given by chaotic sequences U, V, and W. The specific operation is as follows: (4)； (5)； In formula (4), downsampling(-) is the downsampling function; the chaotic sequences U, V, and W generated in formula (1) are sampled every 50 bits to ensure the randomness of the chaotic sequences; in formula (5), mod(-) is the remainder function and floor(-) is the floor function. Random numbers of 0-9 are generated from the downsampled chaotic sequences, and the obtained random numbers of 0-9 are judged to generate random 0 and 1 noise bits.

6. The signal transmission method based on three-dimensional constellation step coding according to claim 5, characterized in that, Step S3 includes: By combining the 64QAM data with the state base using high and low bits, the constellation order transition is achieved. Specifically, the encrypted X, Y, and Z data are composed of (X, Y, Z). Encrypted =(S X + B X S Y + B Y S Z + B Z The results show that by using 512 basic states to encrypt 64QAM data, 32,768 encryption symbols are obtained, thus hiding the 64QAM information within them.

7. A signal transmission method based on three-dimensional constellation step coding according to claim 6, characterized in that, In step S4, for signal transmission, the row and column are subjected to two Inverse Fast Fourier Transform (IFFT) operations, and the frequency domain signal is converted into a time domain signal. Cyclic prefixes and suffixes are added before and after the signal, and then the modulated parallel time domain signal is converted from parallel to serial to a serial signal to enter the optical fiber channel. The reverse operation is performed at the receiving end, and the received signal to be decrypted is obtained after serial-to-parallel conversion, removal of cyclic prefixes and suffixes, and Fourier transformation.

8. A signal transmission method based on three-dimensional constellation step coding according to claim 7, characterized in that, In step S5, the correct key for transmission is obtained using the decision state base. Since the key is cyclically sampled, the key information is compared after extraction, and the information that appears most frequently in each sampling is taken as the final key.

9. A signal transmission method based on three-dimensional constellation step coding according to claim 8, characterized in that, In step S5: For legitimate receivers, decoding is aided by known state base information; points where all three state bases are identical are locked for judgment. In three-dimensional space, due to the periodic arrangement of state bases, there will only be 64 points where all three state bases are identical. In this case, the least Euclidean distance is used to make a judgment on the constellation points that need to be judged. For illegal receivers, under the influence of noise, only brute-force demodulation can be used to calculate the Euclidean distance from each symbol to 32,768 locations, and the smallest distance is the correct location of the symbol.

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