A four-dimensional phase optimization low PAPR method based on fast hartley modulation

Abstract

The application discloses a four-dimensional phase optimization low PAPR method based on fast Hartley modulation, wherein data to be transmitted is firstly subjected to constellation mapping through a four-dimensional phase chaotic shadow code module, wherein three-dimensional coordinate information and a masking factor generated by a steady four-dimensional chaotic system are contained, and optimal information in the four-dimensional space is determined; the data subjected to the four-dimensional constellation mapping is subjected to chaotic phase modulator module fitting four-dimensional data processing, so as to reduce overall signal peak values; and the optimized data is subjected to fast Hartley transformation and is sent into a photonic terahertz channel for transmission. The complexity of the application is significantly reduced. Meanwhile, the introduction of the chaotic system also improves the security of the system.

Description

TECHNICAL FIELD

[0001] The application relates to a four-dimensional phase optimization low PAPR method based on fast Hartley modulation, and belongs to the technical field of optical communication. BACKGROUND

[0002] With the rapid development of 5G, 4K video, cloud computing and other services, China is at the forefront of 5G. Therefore, the communication field in China will face a more extensive space, more new space needs to be expanded, and more new services will be developed. The huge information capacity demand constantly drives 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, more and more attention is paid to the multi-carrier technology 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 technology in which multiple data streams are modulated by mutually orthogonal subcarriers. Since OFDM has robustness against channel dispersion and high spectral efficiency, it is considered as a candidate for indoor optical wireless (OW) systems, especially in intensity modulation direct detection (IM / DD) systems, and has attracted great attention due to the multipath characteristics of indoor OW channels. In fact, the signal processing in OFDM transmission / reception is based on fast Fourier transform to realize OFDM modulation / demodulation. But the transmitted signal is real-valued and unipolar (non-negative), and the Hermitian symmetry condition must be applied in the OFDM encoding process. Intensity modulation and direct detection orthogonal frequency division multiplexing (IMDD-OFDM) system is applied in PON (passive optical network) due to its simple and cost-effective configuration. In addition to the advantages of using OFDM in optical communication, 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 nonlinearities of the transmission fiber. In addition, if the PAPR of the optical OFDM signal is too high, the nonlinear effects of devices such as Mach-Zehnder modulators (MZMs), digital-to-analog converters / analog-to-digital converters (DACs / ADCs) and optical fibers, 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 high bit error rate. How to combine the traditional chaotic encryption method with orthogonal mode division multiplexing to realize high-speed, high-security, large-capacity and low-PAPR transmission is a technical problem that technicians in the field urgently need to solve. SUMMARY

[0005] The application provides a four-dimensional phase optimization low PAPR method based on fast Hartley modulation, aiming at reducing the PAPR while reducing the computational complexity of the system.

[0006] The technical scheme is as follows:

[0007] In the first aspect, the four-dimensional phase optimization low PAPR method based on fast Hartley modulation specifically comprises the following steps.

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

[0009] Step 2: Perform constellation mapping on the encrypted bit sequence to be transmitted by using the masking factors A and B generated by the steady four-dimensional chaotic system, and obtain a 4D-constellation signal.

[0010] Step 3: Perform phase modulation on the 4D-constellation signal by using the masking factor D generated by the steady four-dimensional chaotic system, and obtain K OFDM signals.

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

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

[0013] As a preferred scheme, the method further comprises the following steps.

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

[0015] As a preferred scheme, the step 1 specifically comprises the following steps.

[0016] Step 1.1: Obtain the bit sequence to be transmitted Data.

[0017] Step 1.2: Use the steady four-dimensional chaotic system to obtain a third chaotic sequence The calculation formula of the steady four-dimensional chaotic system is as follows.

[0018]

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

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

[0021]

[0022] wherein mod represents the modulo operation.

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

[0024] baseband_bits = bitxor(Data, C)

[0025] wherein baseband_bits represents the encrypted data stream, and bitxor represents the exclusive or operation of each bit.

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

[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 group of data is mapped by 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 group of data.

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

[0030]

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

[0032] Step 2.4, using the first chaotic sequence Second chaotic sequence Obtain the masking factor A and the masking factor B, and take the masking factor A and the masking factor B as two codebooks A' and B', and the calculation formula of the masking factor A and the masking factor B is as follows:

[0033]

[0034]

[0035] Wherein, fix represents rounding towards zero, floor represents rounding towards negative infinity, and mod represents the modulo operation.

[0036] Step 2.5, alternately fill the 4th dimension coordinates of the four-dimensional constellation of all group data with the two codebooks A' and B', to obtain a 4D-constellation signal.

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

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

[0039] Step 3.2, obtaining a fourth chaotic sequence by using a steady four-dimensional chaotic system The calculation formula of the steady four-dimensional chaotic system is as follows:

[0040]

[0041] Wherein, 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, f are system parameters.

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

[0043]

[0044] Wherein, fix represents rounding towards zero, and mod represents the modulo operation.

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

[0046] Step 3.5, when the number of iterations K of 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 minimum PAPR of each group is selected as the OFDM signal, and K groups of OFDM signals are obtained.

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

[0048] As a preferred scheme, the three-dimensional constellation mapping adopts three-dimensional 16-point double-cubic constellation mapping.

[0049] In a second aspect, a communication system comprises: a transmitting end configured to perform steps 1 to 5 of the high-security-probability shaping method based on three-dimensional constellation joint shaping in the first aspect.

[0050] The communication system further comprises: a receiving end configured to perform step 6 of the high-security-probability shaping method based on three-dimensional constellation joint shaping in the first aspect.

[0051] Beneficial effects: The four-dimensional phase optimization low PAPR method based on fast Hartley modulation provided by the application is different from the traditional scheme using traditional 4D constellation mapping. In the scheme, the chaotic sequence generated by the steady four-dimensional chaotic system is used to complete the insertion of the fourth dimension. At the same time, by using the fast Hartley algorithm instead of the fast Fourier calculation, the calculation complexity of the system is effectively reduced. In addition, by implementing the four-dimensional chaotic shadow code module driven by chaos and using the chaotic phase modulator to complete the partial transmission sequence (PTS) processing of the signal, the PAPR is successfully reduced. Compared with the traditional PTS technology, the complexity of the 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 application has the following advantages:

[0053] 1. The chaotic four-dimensional phase chaotic shadow code module driven by chaos is realized by using the chaotic sequence generated by the steady four-dimensional chaotic system, and the partial transmission sequence (PTS) processing of the signal is completed by means of the chaotic phase modulator.

[0054] 2. In the PTS processing process of the application, the phase factor is used as the system key to provide a huge 10 161 key space, so that the system can resist brute force cracking, thereby enhancing the security of the system.

[0055] 3. The application 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 DRAWINGS

[0056] Figure 1 is a flow chart of the method of the present application.

[0057] Figure 2 is a steady-state four-dimensional chaotic system model, wherein, Figure 2 in (a) is a projection in x-y-z. Figure 2 in (b) is a projection in x-y. Figure 2 in (c) is a projection in x-z. Figure 2 in (d) is a projection in y-z.

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

[0059] Figure 4 is a flow chart of the 8-point radix calculation, wherein, Figure 4 in (a) is a flow chart of the 8-point radix 2DIT-FHT calculation. Figure 4 in (b) is a flow chart of the 8-point radix 2DIT-FFT calculation.

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

[0061] Figure 6 is a schematic diagram of the signal performance after 4D-IFHT and 4D-IFFT modulation, wherein, Figure 6 in (a) is the signal performance after 4D-IFHT and 4D-IFFT modulation of the encrypted 4D-OFDM signal and the signal before encryption. Figure 6 in (b) is the signal performance after 4D-IFHT and 4D-IFFT modulation of the 4D-OFDM.

[0062] Figure 7 is a schematic diagram of the low PAPR performance based on the IFHT algorithm.

[0063] Figure 8 is a schematic diagram of the low PAPR performance based on the IFFT algorithm. DETAILED DESCRIPTION

[0064] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0065] The present application will be further described below with reference to specific embodiments.

[0066] Example 1:

[0067] This embodiment introduces a four-dimensional phase-optimized low PAPR method based on fast Hartley modulation, such as... Figure 1 As shown, at the transmitting end, the data to be transmitted first undergoes constellation mapping via a four-dimensional phase chaotic image coding module. This mapping includes three-dimensional coordinate information and a masking factor generated by a steady-state four-dimensional chaotic system, determining the optimal information in four-dimensional space. After four-dimensional constellation mapping, the data is processed by a chaotic phase modulator module to fit the four-dimensional data, reducing the overall signal peak value. The optimized data undergoes a fast Hartley transform and is then transmitted through a photonic terahertz channel. At the receiving end, the received signal undergoes an inverse fast Hartley transform, and the original data is recovered through four-dimensional chaotic decoding using a masking factor key generated by a steady-state four-dimensional chaotic system. Specifically, this includes:

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

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

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

[0071] Step 4: Distribute the K OFDM signals onto the K subcarriers, and apply the inverse fast Hartley transform to the OFDM signals on the K subcarriers to obtain the time-domain signals.

[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 Hartley inverse transform on the received signal, and use the masking factor generated by the steady-state four-dimensional chaotic system as a key to decode and recover the original data.

[0075] Example 2:

[0076] This embodiment describes a communication system, including: a transmitter, which 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 perform step 6 in a high-security probability shaping method based on three-dimensional constellation joint shaping in Embodiment 1.

[0078] Embodiment 3:

[0079] In order to study the four-dimensional phase optimization low PAPR method based on fast Hartley modulation, the embodiment introduces a steady four-dimensional chaotic system, which includes a four-dimensional phase chaotic shadow code module, a chaotic phase modulator and a fast Hartley transform module. The influence of each module in the steady four-dimensional chaotic system on the 4D-OFDM signal and the influence of the adopted photonic THZ transmission system on the 4D-OFDM signal are as follows:

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

[0081] The equation of the steady four-dimensional chaotic system is as follows:

[0082]

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

[0084] Chaotic sequence of chaotic system And The mask factors A, B, C and D for chaotic driving are generated after processing, and the calculation formula of the mask factors A, B, C and D is as follows:

[0085]

[0086] Wherein, fix represents rounding to zero, floor represents rounding to negative infinity, and mod represents modulo operation.

[0087] When receiving signals encrypted by these complex chaotic trajectories (chaotic sequences), only the accurate initial value (private key) can complete the decryption, thereby ensuring high security performance. Around the four chaotic sequences generated by the super multi-stable four-dimensional chaotic system And As Figure 2The four chaotic sequences are processed to generate the masking factors A, B, C and D shown in (a) to (d) for the four-dimensional phase chaotic shadow code module and the chaotic phase modulator driven by chaos.

[0088] Traditional four-dimensional modulation utilizes four degrees of freedom of light waves to transmit information, including two orthogonal polarization states and their in-phase and quadrature component phase relationships. Compared with two-dimensional modulation, four-dimensional modulation transmits signals in four-dimensional space to improve information transmission capacity. However, unlike polarization multiplexing, there is a correlation between polarization states, increasing the complexity of demodulation, and requiring more complex coherent reception and digital signal processing algorithms.

[0089] Unlike the above method, the present application modulates a four-dimensional data fitting by combining a random signal with a chaotic system. First, a data stream is randomly generated as data to be transmitted. The data to be transmitted is first encrypted by formula (3) to obtain an encrypted data stream, and the calculation formula is as follows:

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

[0091] Wherein, baseband_bits represents the encrypted data stream, bitxor represents the exclusive or operation of each specific bit, Data represents the data to be transmitted, and C represents the masking factor.

[0092] The encrypted data stream is first mapped to a four-dimensional constellation X-axis, Y-axis and Z-axis coordinate by traditional three-dimensional 16-point double-cubic constellation.

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

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

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

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

[0097] The fourth dimension coordinate of the four-dimensional constellation is determined by the masking factor generated by the chaotic system. The method determined by the present application generates two different masking factors A and B by using the chaotic sequence generated by the chaotic system, and uses the masking factors A and B as two codebooks A' and B'. When mapping the fourth dimension coordinate of the four-dimensional constellation for all groups of data, the two codebooks A' and B' are used to fill the fourth dimension coordinate of the four-dimensional constellation of each group of data in turn, the four-dimensional chaotic shadow code encoding is completed, the 4D-constellation signal is obtained, and an overall data stream containing four-dimensional fitting data is formed.

[0098] The 4D-constellation signal of the four-dimensional phase chaotic shadow code module is processed by using a chaotic phase modulator to reduce the overall signal peak value, and the specific process is as follows:

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

[0100] The chaotic system is used to generate a masking factor D corresponding to the number of each sub-sequence as a phase factor W.

[0101] Iterate the cyclic shift, and after each iteration, use the phase factor W to perform phase optimization on each sub-sequence to generate K modulated sequences.

[0102] When the number of iterations of the cyclic shift reaches K, 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 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, and realizes 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 by a sequence generated by chaos. Finally, the PAPR of the entire sequence is calculated, and the sequence with the minimum 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 calculating each sequence is reduced by processing K sequences at the same time. Specifically, for K sequences, the complexity is O(K*N*log(N)) when passing through IFHT (inverse fast Hartley transform) at the same time, while the complexity of passing through IFFT for each sequence is O(K*N^2), where K is the number of sequences and N is the length of each sequence. Since the basic operation number of FHT and IFHT algorithm is logarithmic with sequence length N, the complexity of the first method is usually lower, which fully utilizes the fast calculation advantage of FHT (fast Hartley transform). Second, the overall complexity of the system is reduced by using FHT instead of FFT. From the mathematical calculation, this replacement helps to reduce the complexity of the system, as shown in Figure 3

[0106] Hartley transform can be converted to Fourier transform for N times of addition and multiplication, which is faster than the post-processing in complex numbers. If the source data is valid, FHT can be more efficient than FFT. Fast Hartley transform (FHT) is a high-efficiency transform algorithm for real sequences and closely related to discrete Fourier transform (DFT), which does not need to operate with imaginary parts. The algorithm maps real-valued sequences to real-valued spectra by preserving some useful parts of DFT. Let x(n), n=0,1,2,…,N-1 be an N-point real sequence, and its DHT is defined as:

[0107]

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

[0109]

[0110] Therefore, sometimes it can be avoided to recalculate DHT to DFT, for example, by multiplying a long number proportional and inverse proportional form of Hartley transform can be written as a pair of transforms, where casα=cosα+sinα, Hartley transform is a real triangular transform with self-inverse property. The following is the basic principle of base 2 DIT-FHT operation. Figure 4 The 8-point base 2 DIT-FFT calculation flowchart and the 8-point base 2 DIT-FHT calculation flowchart are shown in FIGS. 1 and 2, respectively.

[0111] Compared with FFT algorithm, the fast algorithm FHT of DHT can reduce nearly half of the calculation amount. The real multiplication times of N-point base 2 time domain decimation fast DHT (base 2 DIT-FHT) algorithm are:​

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

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

[0114]

[0115] where M = log2 N It is easy to know from equation (6) that the number of real multiplications of the radix-2 DIT-FHT algorithm is about half of that of the radix-2 DIT-FFT algorithm, while the FFT needs as high as MN / 2 complex number operations. Therefore, replacing the FFT algorithm with the FHT algorithm can reduce the overall system complexity.

[0116] Example 4:

[0117] This example introduces the experimental process of the method of the application, Figure 5 shows the BER performance of the 4D-OFDM signal after transmission in the seven-core optical fiber for 2 km, and Figure 5 a significant result is observed: within a range of 2 kilometers, the seven-core optical fiber transmission system exhibits excellent performance. Most notably, even in this high bit error rate case, the difference in received optical power between the various fiber cores is very small, less than 0.36 dB. This indicates that the optical fiber transmission system used exhibits excellent stability and uniformity within a range of 2 kilometers. This finding emphasizes the robustness of the system, which can provide consistent performance even under adverse conditions, which is very important for various applications.

[0118] The performance of OFDM signals of different dimensions is tested, and it is found that, compared to 3D-OFDM, 4D-OFDM has a significant improvement of 3.08 dB under the bit error rate threshold condition. The use of the IFHT algorithm instead of the IFFT algorithm further improves 0.32 dB, which is shown in (b) in Figure 6 , verifying that FHT is more accurate than FFT. At the same time, in terms of low PAPR performance and scalability, it is verified in Figure 7 and Figure 8 . The high-security four-dimensional phase optimization low PAPR method based on fast Hartley modulation reduces the PAPR by 3.38 dB when using the IFHT algorithm, and by 2.73 dB when using the IFFT algorithm. Overall, 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 merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A four-dimensional phase optimized low PAPR method based on fast Hartley modulation, characterized in that: Specifically comprising: Step 1: obtaining a bit sequence to be transmitted, using a masking factor C generated by a steady-state four-dimensional chaotic system to encrypt the bit sequence to be transmitted, and obtaining an encrypted bit sequence to be transmitted; Step 2: using the masking factors A and B generated by the steady-state four-dimensional chaotic system to perform constellation mapping on the encrypted bit sequence to be transmitted, and obtaining a 4D-constellation signal; Step 3: using the masking factor D generated by the steady-state four-dimensional chaotic system to perform phase modulation on the 4D-constellation signal, and obtaining K OFDM signals; Step 4: distributing the K OFDM signals to K subcarriers, and using inverse fast Hartley transform on the OFDM signals on the K subcarriers to obtain time domain signals; Step 5: sending the time domain signals to a photonic terahertz channel for transmission; The step 2 specifically comprises: Step 2.1, obtaining the encrypted bit sequence to be transmitted, and grouping the encrypted bit sequence to be transmitted; Step 2.2, performing three-dimensional constellation mapping on each group of data to obtain the coordinates of the X-axis, Y-axis and Z-axis of the four-dimensional constellation corresponding to each group of data; Step 2.3, obtaining a first chaotic sequence by using a steady-state four-dimensional chaotic system , a second chaotic sequence , the steady-state four-dimensional chaotic system has a calculation formula as follows: ； wherein x, y, z, w are state variables, is a first chaotic sequence, is a second chaotic sequence, is a third chaotic sequence, is a fourth chaotic sequence, a, b, c, d, e, f are system parameters, respectively; Step 2.4, using the first chaotic sequence , the second chaotic sequence , obtaining a masking factor A and a masking factor B, taking the masking factor A and the masking factor B as two codebooks A' and B', and the calculation formula of the masking factor A and the masking factor B is as follows: ； ； wherein represents rounding to zero, represents rounding to negative infinity, and mod represents the modulo operation; Step 2.5, alternately using two codebooks A' and B' to fill the fourth-dimensional coordinates of the four-dimensional constellation of all groups of data to obtain a 4D-constellation signal.

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

3. The four-dimensional phase optimization low PAPR method based on fast Hartley modulation according to claim 1, characterized in that: The step 1 specifically comprises: Step 1.1, obtaining a bit sequence to be transmitted Data; Step 1.2, obtaining a third chaotic sequence by using a steady-state four-dimensional chaotic system ; Step 1.3, using the third chaotic sequence A mask factor C is calculated as follows: ； Wherein, mod represents the modulo operation; Step 1.4, encrypting the bit sequence to be transmitted by using the masking factor C to obtain an encrypted bit sequence to be transmitted, and the calculation formula of the encrypted bit sequence to be transmitted is as follows: ； wherein, represents an encrypted data stream, represents an exclusive OR operation on each bit.

4. The four-dimensional phase optimization low PAPR method based on fast Hartley modulation of claim 1, wherein: The step 3 specifically comprises: Step 3.1, obtaining a 4D-constellation signal, and dividing the 4D-constellation signal into K subsequences by using cyclic shift; Step 3.2, obtaining the fourth chaotic sequence by using the steady-state four-dimensional chaotic system ; Step 3.3, using the fourth chaotic sequence , obtaining a masking factor D as the phase factor W, the masking factor D is calculated according to the following formula: ； wherein represents rounding to zero, and mod denotes the modulo operation. Step 3.4, performing iteration of cyclic shift, and performing phase optimization on each subsequence by using a phase factor W after each iteration to generate K modulated sequences; Step 3.5, when the number of iterations of cyclic shift reaches K, 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 an OFDM signal to obtain K groups of OFDM signals.

5. A four-dimensional phase optimization low PAPR method based on fast Hartley modulation according to any one of claims 1, 3 or 4, characterized in that: a=4.8, b=5, c=21.3, d=5, e=0.01, f=0.

1.

6. The four-dimensional phase optimization low PAPR method based on fast Hartley modulation according to claim 1, characterized in that: The three-dimensional constellation mapping uses a three-dimensional 16-point double-cubic constellation mapping.

7. A communication system, characterized by: Comprising: A transmitting end, the transmitting end is used for executing the following steps: Step 1: obtaining a bit sequence to be transmitted, using a masking factor C generated by a steady-state four-dimensional chaotic system to encrypt the bit sequence to be transmitted, and obtaining an encrypted bit sequence to be transmitted; Step 2: using the masking factors A and B generated by the steady-state four-dimensional chaotic system to perform constellation mapping on the encrypted bit sequence to be transmitted, and obtaining a 4D-constellation signal; Step 3: the 4D-constellation signal is phase modulated by the masking factor D generated by the steady four-dimensional chaotic system to obtain K OFDM signals; Step 4: the K OFDM signals are distributed on K subcarriers, and the OFDM signals on the K subcarriers are subjected to inverse fast Hartley transform to obtain time domain signals; Step 5: the time domain signals are sent to a photonic terahertz channel for transmission; The step 2 specifically comprises: Step 2.1: obtaining the encrypted bit sequence to be transmitted, and grouping the encrypted bit sequence to be transmitted; Step 2.2: obtaining the coordinates of the X axis, Y axis and Z axis of the four-dimensional constellation corresponding to each group of data through three-dimensional constellation mapping; Step 2.3, obtaining a first chaotic sequence by using a steady-state four-dimensional chaotic system , a second chaotic sequence , the steady-state four-dimensional chaotic system has a calculation formula as follows: ； wherein x, y, z, w are state variables, is a first chaotic sequence, is a second chaotic sequence, is a third chaotic sequence, is a fourth chaotic sequence, a, b, c, d, e, f are system parameters, respectively; Step 2.4, using the first chaotic sequence , the second chaotic sequence , obtaining a masking factor A and a masking factor B, taking the masking factor A and the masking factor B as two codebooks A' and B', and the calculation formula of the masking factor A and the masking factor B is as follows: ； ； wherein represents rounding to zero, represents rounding to negative infinity, mod represents the modulo operation; Step 2.5: alternately using two codebooks A' and B' to fill the fourth-dimensional coordinates of the four-dimensional constellation of all groups of data to obtain the 4D-constellation signal.

8. A communication system as claimed in claim 7, characterized in that: Further comprising: A receiving end, the receiving end is used for executing the following steps: Subjecting the received signal to inverse fast Hartley transform, and using the masking factor generated by the steady four-dimensional chaotic system as a key to decode and recover the original data.

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