Four-dimensional phase optimization low PAPR method based on rapid Hartley modulation

Abstract

The invention discloses a four-dimensional phase optimization low PAPR method based on fast Hartley modulation, and the method comprises the steps: carrying out the constellation mapping of to-be-transmitted data through a four-dimensional phase chaos shadow code module, enabling the constellation mapping to comprise three-dimensional coordinate information and a masking factor generated by a steady-state four-dimensional chaos system, and determining the optimal information in a four-dimensional space; and the data subjected to four-dimensional constellation mapping is subjected to fitting four-dimensional data processing through the chaos phase modulator module, so that the overall signal peak value is reduced. And carrying out rapid Hartley transformation on the optimized data, and sending the data to a photon terahertz channel for transmission. According to the invention, the complexity is obviously reduced. Meanwhile, the introduction of the chaotic system also improves the safety of the system.

Description

Technical Field

[0001] The invention relates to a four-dimensional phase optimization low PAPR method based on fast Hartley modulation, belonging to the technical field of optical communication. Background Art

[0002] With the rapid development of 5G, 4K video, cloud computing and other services, China is at the forefront of 5G. Therefore, China's communications field will face a wider space, with more new spaces to be expanded and more new services to be developed. The huge demand for information capacity continues to drive the development of long-distance backbone networks and short-distance optical transmission systems, and the expansion of optical communication systems is an eternal topic. Therefore, multi-carrier technology has received more and more attention in optical networks. Multi-carrier technology can provide larger capacity and flexible bandwidth. Multi-carrier technologies such as optical orthogonal frequency division multiplexing (OFDM) have been widely studied.

[0003] Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technique in which multiple data streams are modulated by mutually orthogonal subcarriers. Due to its robustness against channel dispersion and high spectral efficiency, OFDM is considered a candidate for indoor optical wireless (OW) systems, especially in intensity modulation direct detection (IM / DD) systems, and has gained great attention due to the multipath characteristics of indoor OW channels. In fact, signal processing in OFDM transmission / reception is based on fast Fourier transform to achieve OFDM modulation / demodulation. However, its input signal is real-valued and unipolar (non-negative), and Hermitian symmetry conditions must be applied in the OFDM encoding process. Intensity modulation and direct detection orthogonal frequency division multiplexing (IMDD-OFDM) systems are used in PON (passive optical networks) due to their simple and cost-effective configuration. In addition to the advantages of using OFDM in optical communications, there are also some disadvantages that must be considered. High peak to average power ratio (PAPR) is one of the main disadvantages of OFDM systems. Due to the high PAPR, when the transmission power is large, the optical OFDM signal will produce nonlinear distortion due to the nonlinearity of the transmission fiber. In addition, if the PAPR of the optical OFDM signal is too high, the nonlinear effects of devices such as the Mach-Zehnder modulator (MZM), digital-to-analog converter / analog-to-digital converter (DAC / ADC) and optical fiber may cause intermodulation between subcarriers and introduce nonlinear distortion.

[0004] In the existing photonic terahertz communication system, the traditional chaotic encryption method has high security, but its high complexity often leads to long processing time and increased bit error rate. How to combine the traditional chaotic encryption method with orthogonal mode division multiplexing to achieve high-speed, high-security, large-capacity and signal PAPR-reducing transmission is a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0005] Objective: To overcome the shortcomings of the prior art, the present invention provides a four-dimensional phase-optimized low PAPR method based on fast Hartley modulation, which aims to reduce the computational complexity of the system while reducing the PAPR. In addition, the scheme also uses a chaotic system to improve the reliability and robustness of the photonic terahertz communication system, thereby maximizing the anti-interference and transmission reliability of the entire transmission system.

[0006] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0007] In the first aspect, a four-dimensional phase optimized low PAPR method based on fast Hartley modulation specifically includes:

[0008] Step 1: Obtain a bit sequence to be transmitted, and use a masking factor C generated by a steady-state four-dimensional chaotic system to encrypt the bit sequence to be transmitted by the masking factor C to obtain an encrypted bit sequence to be transmitted.

[0009] Step 2: The encrypted bit sequence to be transmitted is constellated using masking factors A and B generated by a steady-state four-dimensional chaotic system to obtain a 4D-constellation signal.

[0010] Step 3: Phase modulate the 4D-constellation signal using the masking factor D generated by the steady-state four-dimensional chaotic system to obtain K OFDM signals.

[0011] Step 4: Allocate the K OFDM signals to K subcarriers, and use the inverse fast Hartley transform on the OFDM signals on the K subcarriers to obtain the time domain signal.

[0012] Step 5: Send the time domain signal into the photonic terahertz channel for transmission.

[0013] As a preferred solution, it also includes:

[0014] Step 6: Perform a fast inverse Hartley transform on the received signal and use the masking factor generated by the steady-state four-dimensional chaotic system as the key to decode and recover the original data.

[0015] As a preferred solution, the step 1 specifically includes:

[0016] Step 1.1, obtain the bit sequence Data to be transmitted.

[0017] Step 1.2: Using the steady-state four-dimensional chaotic system, obtain the third chaotic sequence The calculation formula of the steady-state four-dimensional chaotic system is as follows:

[0018]

[0019] Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, and a, b, c, d, e, and f are system parameters respectively.

[0020] Step 1.3, using the third chaotic sequence Calculate the mask factor C. The calculation formula of the mask factor C is as follows:

[0021]

[0022] Here, mod represents the modulo operation.

[0023] Step 1.4, encrypt the bit sequence to be transmitted by using the masking factor C to obtain the encrypted bit sequence to be transmitted. The calculation formula of the encrypted bit sequence to be transmitted is as follows:

[0024] baseband_bits=bitxor(Data,C)

[0025] Among them, baseband_bits represents the encrypted data stream, and bitxor represents the XOR operation on each bit.

[0026] As a preferred solution, the step 2 specifically includes:

[0027] Step 2.1, obtaining the encrypted bit sequence to be transmitted, and grouping the encrypted bit sequence to be transmitted.

[0028] Step 2.2, each set of data is mapped through a three-dimensional constellation to obtain the coordinates of the X-axis, Y-axis and Z-axis of the four-dimensional constellation corresponding to each set of data.

[0029] Step 2.3, using the steady-state four-dimensional chaotic system, obtain the first chaotic sequence The second chaotic sequence The calculation formula of the steady-state four-dimensional chaotic system is as follows:

[0030]

[0031] Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, and a, b, c, d, e, and f are system parameters respectively.

[0032] Step 2.4, using the first chaotic sequence The second chaotic sequence Obtain a masking factor A and a masking factor B, and use the masking factor A and the masking factor B as two codebooks A' and B'. The calculation formulas of the masking factor A and the masking factor B are as follows:

[0033]

[0034]

[0035] Among them, fix means rounding towards zero, floor means rounding towards negative infinity, and mod means modulo operation.

[0036] Step 2.5: Use two codebooks A' and B' in turn to fill the 4th dimension coordinates of the 4D constellations of all groups of data to obtain 4D-constellation signals.

[0037] As a preferred solution, the step 3 specifically includes:

[0038] Step 3.1, obtaining a 4D-constellation signal, and dividing the 4D-constellation signal into K subsequences by using cyclic shift.

[0039] Step 3.2: Using the steady-state four-dimensional chaotic system, obtain the fourth chaotic sequence The calculation formula of the steady-state four-dimensional chaotic system is as follows:

[0040]

[0041] Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, and a, b, c, d, e, and f are system parameters respectively.

[0042] Step 3.3, using the fourth chaotic sequence Obtain a masking factor D as the phase factor W, and the calculation formula of the masking factor D is as follows:

[0043]

[0044] Among them, fix means rounding towards zero, and mod means modulo operation.

[0045] Step 3.4, iterate the cyclic shift, and after each iteration, use the phase factor W to optimize the phase of each subsequence to generate K modulated sequences.

[0046] Step 3.5, when the number of iterations of the cyclic shift is reached, K groups of K modulated sequences are generated, the PAPR of each group of K modulated sequences is calculated, and the modulated sequence with the smallest PAPR in each group is selected as the OFDM signal to obtain K groups of OFDM signals.

[0047] As a preferred embodiment, a=4.8, b=5, c=21.3, d=5, e=0.01, and f=0.1.

[0048] As a preferred solution, the three-dimensional constellation mapping adopts three-dimensional 16-point dual cube constellation mapping.

[0049] In a second aspect, a communication system includes: a transmitting end, wherein the transmitting end is used to execute steps 1 to 5 in a high-security probability shaping method based on three-dimensional constellation joint shaping in the first aspect.

[0050] It also includes: a receiving end, which is used to execute step 6 in the high-security probability shaping method based on three-dimensional constellation joint shaping in the first aspect.

[0051] Beneficial effects: The present invention provides a four-dimensional phase-optimized low PAPR method based on fast Hartley modulation. Unlike the traditional 4D constellation mapping used in the traditional scheme, this scheme uses a chaotic sequence generated by a steady-state four-dimensional chaotic system to complete the insertion of the fourth dimension. At the same time, by adopting the fast Hartley algorithm instead of the fast Fourier calculation, the computational complexity of the system is effectively reduced. In addition, the PAPR is successfully reduced by implementing a chaos-driven four-dimensional chaotic shadow code module and using a chaotic phase modulator to complete the partial transmission sequence (PTS) processing of the signal. Compared with the traditional PTS technology, the complexity of this scheme is significantly reduced. At the same time, the introduction of the chaotic system also improves the security of the system.

[0052] Compared with the prior art, the advantages of the present invention are:

[0053] 1. The present invention realizes a chaos-driven four-dimensional phase chaos shadow code module by utilizing the chaotic sequence generated by a steady-state four-dimensional chaotic system, and completes the partial transmission sequence (PTS) processing of the signal with the help of a chaotic phase modulator.

[0054] 2. In the PTS processing process of the present invention, the phase factor is used as the system key, providing a huge 10 161 The key space enables the system to resist brute force cracking, thereby enhancing the security of the system.

[0055] 3. The present invention adopts fast Hartley modulation, has greater signal gain and better PAPR performance, and the PAPR is reduced by 3.38dB, which has very reliable and practical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic diagram of the process of the present invention.

[0057] Figure 2 is a steady-state four-dimensional chaotic system model, in which Figure 2 The middle figure (a) is the projection in xyz. Figure 2 The middle figure (b) is the projection in xy. Figure 2 The middle figure (c) is the projection in xz; Figure 2 The middle figure (d) is the projection in yz.

[0058] Figure 3 Block diagram of the principle of using a chaotic phase optimized modulator combined with fast Hartley modulation.

[0059] Figure 4 This is an 8-point basis calculation flow chart, where: Figure 4 The middle figure (a) is the 8-point basis 2DIT-FHT calculation flow chart. Figure 4 The middle figure (b) is the 8-point 2DIT-FFT calculation flow chart.

[0060] Figure 5 Schematic diagram of the bit error rate performance of the 4D-OFDM signal system under different cores.

[0061] Figure 6 Schematic diagram of signal performance after 4D-IFHT and 4D-IFFT modulation, where: Figure 6 The middle figure (a) shows the signal performance after 4D-IFHT and 4D-IFFT modulation in the encrypted 4D-OFDM signal and the unencrypted signal. Figure 6 The middle figure (b) shows the signal performance after 4D-IFHT and 4D-IFFT modulation in 4D-OFDM.

[0062] Figure 7 Schematic diagram of low PAPR performance based on IFHT algorithm.

[0063] Figure 8 Schematic diagram of low PAPR performance based on IFFT algorithm. DETAILED DESCRIPTION

[0064] The following is a clear and complete description of the technical solutions in the examples of the present invention in conjunction with the accompanying drawings in the examples 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 those skilled in the art without creative work are within the protection scope of the present invention.

[0065] The present invention will be further described below in conjunction with specific embodiments.

[0066] Embodiment 1:

[0067] This embodiment introduces a four-dimensional phase optimization low PAPR method based on fast Hartley modulation, such as Figure 1 As shown, at the transmitting end, the data to be transmitted is firstly constellated by the four-dimensional phase chaos shadow code module, which contains three-dimensional coordinate information and the masking factor generated by the steady-state four-dimensional chaotic system, and determines the optimal information in the four-dimensional space. The data after the four-dimensional constellation mapping is processed by fitting the four-dimensional data by the chaotic phase modulator module to reduce the overall signal peak. The optimized data is subjected to a fast Hartley transform and sent to the photonic terahertz channel for transmission. At the receiving end, the received signal is subjected to a fast inverse Hartley transform, and the masking factor key generated by the steady-state four-dimensional chaotic system is used to perform four-dimensional chaos decoding to restore the original data. Specifically, it includes:

[0068] Step 1: Obtain a bit sequence to be transmitted, and use a masking factor C generated by a steady-state four-dimensional chaotic system to encrypt the bit sequence to be transmitted by the masking factor C to obtain an encrypted bit sequence to be transmitted.

[0069] Step 2: The encrypted bit sequence to be transmitted is constellated using masking factors A and B generated by a steady-state four-dimensional chaotic system to obtain a 4D-constellation signal.

[0070] Step 3: Phase modulate the 4D-constellation signal using the masking factor D generated by the steady-state four-dimensional chaotic system to obtain K OFDM signals.

[0071] Step 4: Allocate the K OFDM signals to K subcarriers, and use the inverse fast Hartley transform on the OFDM signals on the K subcarriers to obtain the time domain signal.

[0072] Step 5: Send the time domain signal into the photonic terahertz channel for transmission.

[0073] Furthermore, it also includes:

[0074] Step 6: Perform a fast inverse Hartley transform on the received signal and use the masking factor generated by the steady-state four-dimensional chaotic system as the key to decode and recover the original data.

[0075] Embodiment 2:

[0076] This embodiment introduces a communication system, including: a transmitting end, wherein the transmitting end is used to execute steps 1 to 5 in a high-security probability shaping method based on three-dimensional constellation joint shaping in embodiment 1.

[0077] It also includes: a receiving end, which is used to execute step 6 in the high-security probability shaping method based on three-dimensional constellation joint shaping in Example 1.

[0078] Embodiment 3:

[0079] In order to study the four-dimensional phase optimization low PAPR method based on fast Hartley modulation of the present invention, this embodiment introduces a steady-state four-dimensional chaotic system, including: a four-dimensional phase chaos shadow code module, a chaotic phase modulator, and a fast Hartley transformation module. The influence of each module in the steady-state four-dimensional chaotic system on the 4D-OFDM signal and the influence of the adopted photon THZ transmission system on the 4D-OFDM signal are specifically as follows:

[0080] In the chaos-driven four-dimensional phase chaos shadow code module, chaos phase modulator and fast Hartley transform module, a steady-state four-dimensional chaotic system is used to complete the chaos driving of the four-dimensional phase chaos shadow code module, chaos phase modulator and fast Hartley transform module.

[0081] Among them, the equation of the steady-state four-dimensional chaotic system is as follows:

[0082]

[0083] Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, a, b, c, d, e, and f are system parameters. When a=4.8, b=5, c=21.3, d=5, e=0.01, and f=0.1, the system can become hyperchaotic.

[0084] Chaotic Sequences of Chaotic Systems and After processing, mask factors A, B, C and D for chaos driving are generated. The calculation formulas of mask factors A, B, C and D are as follows:

[0085]

[0086] Among them, fix means rounding towards zero, floor means rounding towards negative infinity, and mod means modulo operation.

[0087] When receiving a signal encrypted by these complex chaotic trajectories (chaotic sequences), only with the accurate initial value (private key) can decryption be completed, thus ensuring high security performance. and like Figure 2As shown in (a) to (d), four chaotic sequences are processed to generate masking factors A, B, C, and D, which are used for a chaotically driven four-dimensional phase chaotic shadow code module and a chaotic phase modulator.

[0088] Traditional four-dimensional modulation uses the four degrees of freedom of light waves to transmit information, including two orthogonal polarization states and the phase relationship between their in-phase and orthogonal components. Compared with two-dimensional modulation, four-dimensional modulation transmits signals in four-dimensional space, improving information transmission capacity, but unlike polarization multiplexing, there is a correlation between polarization states, which increases the complexity of demodulation and requires more complex coherent reception and digital signal processing algorithms.

[0089] Different from the above method, the present invention uses a combination of random signals and chaotic systems to modulate a fitted four-dimensional data. First, a data stream is randomly generated as the data to be transmitted. The data stream to be transmitted is first encrypted by formula (3) to obtain an encrypted data stream. The calculation formula is as follows:

[0090] baseband_bits=bitxor(Data,C) (3)

[0091] Among them, baseband_bits represents the encrypted data stream, bitxor represents the XOR operation on each bit, Data represents the data to be transmitted, and C represents the masking factor.

[0092] The encrypted data stream is first mapped to a traditional three-dimensional 16-point dual-cube constellation to obtain the coordinates of the X-axis, Y-axis, and Z-axis of the four-dimensional constellation.

[0093] For example, when each set of data is 00, the coordinates mapped to the X-axis, Y-axis, and Z-axis are (1,1,1).

[0094] When each set of data is 01, the coordinates mapped to the X-axis, Y-axis, and Z-axis are (-1, -1, 1).

[0095] When each set of data is 10, the coordinates mapped to the X-axis, Y-axis, and Z-axis are (-1, 1, -1).

[0096] When each set of data is 11, the coordinates mapped to the X-axis, Y-axis, and Z-axis are (1,-1,-1).

[0097] The 4th dimension coordinate of the 4D constellation is determined by the masking factor generated by the chaotic system. The method determined by the present invention uses the chaotic sequence generated by the chaotic system to generate two completely different masking factors A and B, and uses the masking factors A and B as two codebooks A' and B'. When the 4th dimension coordinate of the 4D constellation is mapped to all groups of data, the two codebooks A' and B' are used in turn to fill the 4th dimension coordinate of the 4D constellation of each group of data, and the 4D chaotic shadow code encoding is completed to obtain the 4D-constellation signal, forming an overall data stream containing 4D fitting data.

[0098] Through the 4D-constellation signal of the four-dimensional phase chaos shadow code module, the chaotic phase modulator is used to process the fitted four-dimensional data to reduce the overall signal peak, as follows:

[0099] The 4D-constellation signal is divided into K subsequences by cyclic shift, and each subsequence forms a segment in the time domain. Unlike the traditional PTS scheme, the weights of these subsequences are equal, that is, their contributions are the same.

[0100] The chaotic system is used to generate the masking factor D corresponding to each subsequence as the phase factor W.

[0101] The cyclic shift is iterated, and after each iteration, the phase factor W is used to optimize the phase of each subsequence to generate K modulated sequences.

[0102] When the number of iterations of the cyclic shift is reached, K groups of K modulated sequences are generated, the PAPR of each group of K modulated sequences is calculated, the modulated sequence with the smallest PAPR in each group is selected as the OFDM signal, and the K groups of OFDM signals are transmitted.

[0103] The chaotic phase modulator provides more candidate OFDM signals, increases the randomness of the sequence, and improves the probability of obtaining the best OFDM signal.

[0104] The fast Hartley transform module is used to complete the modulation of the OFDM signal by using the inverse fast Hartley transform, thereby realizing the simultaneous transmission of K groups of OFDM signals.

[0105] In this process, the transmission performance is optimized by phase adjustment. This phase modulation is achieved through a chaotically generated sequence. Finally, the PAPR of the entire sequence is calculated, and the sequence with the smallest PAPR is extracted for transmission. At this time, the phase factor is also one of the keys in the encryption scheme. In the entire scheme, two aspects of computational complexity are successfully reduced: First, in the phase modulation part, the computational complexity of sequence-by-sequence calculation is reduced by processing K sequences simultaneously. Specifically, for K sequences to pass through IFHT (Inverse Fast Hartley Transform) at the same time, the complexity is O(K*N*log(N)); while the complexity of passing through IFFT sequence by sequence is O(K*N^2), where K is the number of sequences and N is the length of each sequence. Since the number of basic operations of the FHT and IFHT algorithms is logarithmically related to the sequence length N, the complexity of the first method is usually lower, making full use of the fast calculation advantage of FHT (Fast Hartley Transform). Secondly, the overall complexity of the system is reduced by replacing FFT with FHT. From a mathematical point of view, this replacement helps to reduce the complexity of the system, such as Figure 3 shown.

[0106] The Hartley transform can be converted to a Fourier transform for N additions and multiplications, which is faster than post-processing in complex numbers. If the source data is valid, FHT may be more efficient than FFT. The Fast Hartley Transform (FHT) is an efficient transform algorithm for real sequences that is closely related to the Discrete Fourier Transform (DFT) and does not require operations with the imaginary part. The algorithm maps a real-valued sequence to a real-valued spectrum by retaining some useful parts of the DFT. Let x(n), n=0,1,2,…,N-1 be an N-point real sequence, then its DHT is defined as:

[0107]

[0108] The corresponding inverse DHT transform is defined as:

[0109]

[0110] Therefore, it is sometimes possible to avoid recalculating the DHT to DFT, for example by multiplying by a long number. The direct and inverse forms of the Hartley transform can be written as a pair of transforms, where casα = cosα + sinα. The Hartley transform is a real trigonometric transform with a self-inverse property. The following is the basic principle of the base 2 DIT-FHT operation. Figure 4 They are the 8-point basis 2DIT-FFT calculation flow chart and the 8-point basis 2DIT-FHT calculation flow chart respectively.

[0111] Compared with the FFT algorithm, the fast DHT algorithm FHT can reduce the amount of calculation by nearly half. The number of real multiplications of the N-point radix-2 time-domain extraction fast DHT (radix-2 DIT-FHT) algorithm is:

[0112] M FHT =NM-3N+4 (6)

[0113] The number of real number additions of the N-point 2DIT-FHT algorithm is:

[0114]

[0115] Where M = log2 N According to formula (6), the number of real multiplications of the radix 2DIT-FHT algorithm is about half of that of the radix 2DIT-FFT algorithm, while FFT requires up to MN / 2 complex operations. Therefore, replacing the FFT algorithm with the FHT algorithm can reduce the overall system complexity.

[0116] Embodiment 4:

[0117] This embodiment introduces the experimental process of the method of the present invention. Figure 5 The BER performance of the 4D-OFDM signal after 2 km transmission in a seven-core fiber is shown. Figure 5 A remarkable result was observed: the seven-core fiber transmission system showed excellent performance over a 2 km range. Most notably, even at this high bit error rate, the difference in received optical power between the individual fiber cores was very small, less than 0.36 dB. This indicates that the adopted fiber transmission system showed excellent stability and uniformity over a 2 km range. This finding emphasizes the robustness of the system, which can provide consistent performance even under adverse conditions, which is very important for a variety of applications.

[0118] The performance of OFDM signals in different dimensions was tested, and under the condition of bit error rate threshold, it was found that compared with 3D-OFDM, 4D-OFDM had a significant improvement of 3.08dB. Using the IFHT algorithm instead of the IFFT algorithm further improved it by 0.32dB. Figure 6 As shown in (b), FHT is more accurate than FFT. At the same time, in terms of low PAPR performance and scalability, Figure 7 and Figure 8 The high-security four-dimensional phase optimization low PAPR method based on fast Hartley modulation of the present invention reduces PAPR by 3.38dB when the IFHT algorithm is used, and reduces it by 2.73dB when the IFFT algorithm is used. In general, the four-dimensional phase optimization low PAPR scheme based on fast Hartley modulation performs well in signal noise reduction and PAPR reduction, especially when IFHT is used instead of IFFT.

[0119] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A four-dimensional phase optimized low PAPR method based on fast Hartley modulation, characterized in that: Specifically include: Step 1: Obtain a bit sequence to be transmitted, and use a masking factor C generated by a steady-state four-dimensional chaotic system to encrypt the bit sequence to be transmitted by the masking factor C to obtain an encrypted bit sequence to be transmitted; Step 2: The encrypted bit sequence to be transmitted is constellated using masking factors A and B generated by a steady-state four-dimensional chaotic system to obtain a 4D-constellation signal; Step 3: Phase modulate the 4D-constellation signal using the masking factor D generated by the steady-state four-dimensional chaotic system to obtain K OFDM signals; Step 4: Allocate K OFDM signals to K subcarriers, and use inverse fast Hartley transform on the OFDM signals on the K subcarriers to obtain time domain signals; Step 5: Send the time domain signal into the photonic terahertz channel for transmission.

2. The four-dimensional phase optimized low PAPR method based on fast Hartley modulation according to claim 1, characterized in that: Also includes: Step 6: Perform a fast inverse Hartley transform on the received signal and use the masking factor generated by the steady-state four-dimensional chaotic system as the key to decode and recover the original data.

3. A four-dimensional phase optimized low PAPR method based on fast Hartley modulation according to claim 1 or 2, characterized in that: The step 1 specifically includes: Step 1.1, obtaining the bit sequence Data to be transmitted; Step 1.2: Using the steady-state four-dimensional chaotic system, obtain the third chaotic sequence The calculation formula of the steady-state four-dimensional chaotic system is as follows: Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, a, b, c, d, e, and f are system parameters respectively; Step 1.3, using the third chaotic sequence Calculate the mask factor C. The calculation formula of the mask factor C is as follows: Among them, mod represents the modulo operation; Step 1.4, encrypt the bit sequence to be transmitted by using the masking factor C to obtain the encrypted bit sequence to be transmitted. The calculation formula of the encrypted bit sequence to be transmitted is as follows: baseband_bits=bitxor(Data,C) Among them, baseband_bits represents the encrypted data stream, and bitxor represents the XOR operation on each bit.

4. A four-dimensional phase optimized low PAPR method based on fast Hartley modulation according to claim 1 or 2, characterized in that: The step 2 specifically includes: Step 2.1, obtaining the encrypted bit sequence to be transmitted, and grouping the encrypted bit sequence to be transmitted; Step 2.2, each set of data is mapped through a three-dimensional constellation to obtain the coordinates of the X-axis, Y-axis and Z-axis of the four-dimensional constellation corresponding to each set of data; Step 2.3, using the steady-state four-dimensional chaotic system, obtain the first chaotic sequence The second chaotic sequence The calculation formula of the steady-state four-dimensional chaotic system is as follows: Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, a, b, c, d, e, and f are system parameters respectively; Step 2.4, using the first chaotic sequence The second chaotic sequence Obtain a masking factor A and a masking factor B, and use the masking factor A and the masking factor B as two codebooks A' and B'. The calculation formulas of the masking factor A and the masking factor B are as follows: Among them, fix means rounding towards zero, floor means rounding towards negative infinity, and mod means modulo operation; Step 2.5: Use two codebooks A' and B' in turn to fill the 4th dimension coordinates of the 4D constellations of all groups of data to obtain 4D-constellation signals.

5. A four-dimensional phase optimized low PAPR method based on fast Hartley modulation according to claim 1 or 2, characterized in that: The step 3 specifically includes: Step 3.1, obtaining a 4D-constellation signal, and dividing the 4D-constellation signal into K subsequences by using cyclic shift; Step 3.2: Using the steady-state four-dimensional chaotic system, obtain the fourth chaotic sequence The calculation formula of the steady-state four-dimensional chaotic system is as follows: Among them, x, y, z, w are state variables, is the first chaotic sequence, is the second chaotic sequence, is the third chaotic sequence, is the fourth chaotic sequence, a, b, c, d, e, and f are system parameters respectively; Step 3.3, using the fourth chaotic sequence Obtain a masking factor D as the phase factor W, and the calculation formula of the masking factor D is as follows: Among them, fix means rounding to zero, and mod means modulo operation; Step 3.4, iterate the cyclic shift, and after each iteration, use the phase factor W to optimize the phase of each subsequence to generate K modulated sequences; Step 3.5, when the number of iterations of the cyclic shift is reached, K groups of K modulated sequences are generated, the PAPR of each group of K modulated sequences is calculated, and the modulated sequence with the smallest PAPR in each group is selected as the OFDM signal to obtain K groups of OFDM signals.

6. A four-dimensional phase optimized low PAPR method based on fast Hartley modulation according to any one of claims 3, 4 or 5, characterized in that: a=4.8, b=5, c=21.3, d=5, e=0.01, f=0.

1.

7. The four-dimensional phase optimized low PAPR method based on fast Hartley modulation according to claim 4, characterized in that: The three-dimensional constellation mapping adopts three-dimensional 16-point dual cube constellation mapping.

8. A communication system, characterized in that: include: The transmitting end is used to perform the following steps: Step 1: Obtain a bit sequence to be transmitted, and use a masking factor C generated by a steady-state four-dimensional chaotic system to encrypt the bit sequence to be transmitted by the masking factor C to obtain an encrypted bit sequence to be transmitted; Step 2: The encrypted bit sequence to be transmitted is constellated using masking factors A and B generated by a steady-state four-dimensional chaotic system to obtain a 4D-constellation signal; Step 3: Phase modulate the 4D-constellation signal using the masking factor D generated by the steady-state four-dimensional chaotic system to obtain K OFDM signals; Step 4: Allocate K OFDM signals to K subcarriers, and use inverse fast Hartley transform on the OFDM signals on the K subcarriers to obtain time domain signals; Step 5: Send the time domain signal into the photonic terahertz channel for transmission.

9. A communication system according to claim 8, characterized in that: Also includes: The receiving end is used to perform the following steps: The received signal is subjected to a fast inverse Hartley transform, and the masking factor generated by the steady-state four-dimensional chaotic system is used as the key to decode and recover the original data.

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