PDM optical communication system-oriented three-dimensional low-complexity probabilistic shaping coding method

Abstract

The invention discloses a three-dimensional low-complexity probabilistic shaping coding method for a PDM optical communication system, and the method comprises the steps: carrying out the 3D-QPSK constellation mapping of a high-power signal, and obtaining a processed high-power signal. And after weight-driven bit inversion processing is carried out on the low-power signal, 3D-8QAM constellation mapping is carried out, and a processed low-power signal is obtained. And carrying out PDM superposition on the processed high-power signal and the processed low-power signal to obtain a 3D-32QAM signal after probability shaping. The PDM and WDBR-PS technologies are applied to the three-dimensional constellation, the WDBR technology only needs to be operated in the bit dimension, and the hardware burden of a PDM system sensitive to resource allocation cannot be increased. Meanwhile, by expanding a two-dimensional constellation to a three-dimensional constellation, not only is the PAPR of the OFDM signal effectively reduced, but also the problem that the bit error rate is suddenly increased due to the fact that the distance between constellation points is too small in high-order modulation is avoided.

Description

Technical Field

[0001] The invention relates to a three-dimensional low-complexity probability shaping coding method for a PDM optical communication system, belonging to the technical field of optical communication. Background Art

[0002] With the rapid development of cutting-edge technologies such as 6G, virtual reality, and cloud computing, the number of Internet users and terminal devices has increased dramatically, resulting in a surge in data transmission demand, and the capacity of communication networks is urgently needed. As the main medium for information transmission, optical fiber communication is facing the challenge of how to cope with large-scale data transmission under limited resources. In this context, power domain multiplexing (PDM) technology has emerged. As a key means to improve the capacity of optical fiber communication, PDM uses power differences to achieve multiplexing of multiple information streams based on the same codebook, time, and frequency resources. In addition, power multiplexing technology can be compatible with a variety of other multiplexing and modulation technologies, such as orthogonal frequency division multiplexing (OFDM), to further improve system performance. This integration not only retains the strong dispersion tolerance of multi-carrier technology, but also further optimizes the utilization efficiency of spectrum resources. Especially in the face of the growing bandwidth requirements of modern optical communication systems, PDM-OFDM provides an efficient and reliable solution to help promote the development of next-generation high-speed optical fiber networks. However, a major disadvantage of OFDM signals is their high peak-to-average power ratio (PAPR). This is because OFDM signals are composed of multiple subcarriers, and at certain moments, the phases of these subcarriers may reach peak values ​​simultaneously, causing a significant increase in the instantaneous power of the signal. The introduction of power reuse technology will further increase the PAPR.

[0003] High PAPR will lead to reduced efficiency of the power amplifier and produce large nonlinear distortion. At present, many researchers have conducted extensive research on PAPR suppression, mainly including limiting technology, coding technology and constellation expansion technology. Constellation expansion technology reduces PAPR by changing the position of constellation points. Compared with the first two technologies, it can not only avoid signal distortion, but also effectively reduce PAPR while maintaining relatively low complexity. Studies have shown that the PAPR of 3DOFDM is 2dB lower than that of 2DOFDM. In addition, the expansion of the traditional two-dimensional constellation to three dimensions significantly improves the utilization of the constellation space. Under the same transmission power conditions, this expansion can increase the minimum Euclidean distance (MED) of the constellation points, thereby reducing the problem of increased bit error rate due to the increase in modulation order.

[0004] With the rapid expansion of optical network infrastructure, the demand for high-speed and large-capacity transmission technology is increasing. Although 3D OFDM has significantly improved the spectrum utilization and anti-interference ability of the system. However, with the continuous growth of communication needs, further optimizing signal transmission has become the key. On this basis, constellation shaping technology is introduced. Constellation shaping technology optimizes the distribution of constellation points by redesigning the modulation format. It is mainly divided into probability shaping (PS) and geometric shaping (GS). Probabilistic shaping reduces the average transmission power by changing the transmission probability of constellation points, while improving the spectrum utilization, making the system closer to the Shannon limit; geometric shaping adjusts the spatial position of the constellation points and optimizes the geometric structure of the constellation diagram, so that the average power of the signal is reduced while the minimum Euclidean distance of the constellation points is maintained, thereby improving the anti-interference ability and bit error rate performance of the system. By combining geometric shaping with probability shaping, the anti-interference ability and adaptability of the system can be enhanced while improving the spectrum utilization. These two technologies have become research hotspots in the field of optical communications. Among them, probability shaping technology has high flexibility and performance advantages in the field of constellation shaping, and has become one of the main directions of current research.

[0005] The existing more mature PS technology methods include many-to-one mapping, distribution matcher, variable length coding and adaptive probability shaping. These methods usually rely on complex calculations and mapping mechanisms, and require additional hardware modules to perform encoding and decoding operations. Especially in high-order modulation and high-speed communication environments, these calculation complexities and resource requirements will increase significantly. Therefore, how to combine PS technology with PDM systems is a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0006] Purpose: In order to overcome the fact that the PDM technology in the prior art is very sensitive to resource allocation, it is necessary to accurately control signal power and resource allocation to ensure the stable superposition of multi-layer signals. If the traditional PS technology is applied to the PDM system, it will further aggravate the consumption of hardware resources and system complexity, and reduce the real-time performance and resource management efficiency of the system. The present invention provides a three-dimensional low-complexity probability shaping coding method for PDM optical communication systems.

[0007] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0008] In a first aspect, a three-dimensional low-complexity probability shaping encoding method for a PDM optical communication system comprises the following steps:

[0009] Step 1: Perform 3D-QPSK constellation mapping on the high-power signal in the power multiplexed signal at the transmitting end to obtain a processed high-power signal.

[0010] Step 2: After performing weight-driven bit inversion processing on the low-power signal in the power-multiplexed signal at the transmitting end, 3D-8QAM constellation mapping is performed to obtain a processed low-power signal.

[0011] Step 3: Perform PDM superposition on the processed high-power signal and the processed low-power signal to obtain a probability-shaped 3D-32QAM signal.

[0012] Step 4: Map the 3D-32QAM signal to each subcarrier in the OFDM system. After completing the subcarrier mapping, use the inverse frequency domain transform to convert the 3D-OFDM signal in the frequency domain into a time domain signal.

[0013] Step 5: Add a cyclic prefix before each 3D-OFDM time domain signal to obtain the added 3D-OFDM time domain.

[0014] As a preferred solution, the expression of the signal after power multiplexing is as follows:

[0015]

[0016] Among them, s represents the signal after power multiplexing, p1 represents the power proportion of the high-power signal, and p2 represents the power proportion of the low-power signal. s1 represents a high-power signal, and s2 represents a low-power signal.

[0017] As a preferred solution, the step 1 specifically includes:

[0018] Step 1.1: Obtain a high-power signal that accounts for a relatively large proportion of the power in the power-multiplexed signal at the transmitting end.

[0019] Step 1.2: Group the bit stream of the high-power signal into 2-bit groups.

[0020] Step 1.3: Perform constellation mapping on the data in each group according to 3D-QPSK to obtain the constellation coordinate point of each group.

[0021] Step 1.4: The four grouped constellation coordinate points are regarded as a constellation mapping unit, and all the constellation mapping units are regarded as processed high-power signals.

[0022] As a preferred solution, the step 1.3 specifically includes:

[0023] Step 1.3.1: When the data in the group is 00, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (1, 0, 1).

[0024] Step 1.3.2: When the data in the group is 01, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, 1).

[0025] Step 1.3.3: When the data in the group is 11, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, -1).

[0026] Step 1.3.4: When the data in the group is 10, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, 1).

[0027] As a preferred solution, the weight-driven bit inversion process in step 2 specifically includes:

[0028] Step 2.1.1: Obtain the low-power signal in the power-multiplexed signal of the transmitter, and divide the M-bit data of the low-power signal into three parallel sequences G1, G2 and G3, where the length of G1 is (3 / 7)M, and the lengths of G2 and G3 are both (2 / 7)M.

[0029] Step 2.1.2: Group the bit streams in groups of k bits each for both G2 and G3, and add an extra bit EWB (R i ), add an extra bit EWB (H) before each bit group of G3 i ), where EWB(R i ) represents the effective weighted bit of the ith group in G2, EWB(H i ) represents the effective weighted position of the ith group in G3, and k is an integer greater than or equal to 2 as the decision weight.

[0030] Step 2.1.3: In the bit weighted decision process, if the number of "1" in the bit group of G2 or G3 is less than k / 2, the corresponding EWB (R i ) and EWB(H i ) is set to "1", and the data in the bit group of G2 or G3 is bit-reversed. If the number of "1" in the bit group of G2 or G3 is greater than or equal to k / 2, the corresponding EWB (R i ) and EWB(H i ) is set to "0", and the data bits in the bit group of G2 or G3 remain unchanged. As a key step of WDBR, the bit reversal operation is used to amplify the probability of bit "1" in sequences G2 and G3 before 3D-8QAM mapping.

[0031] Step 2.1.4: After the reversal operation is completed, all EWBs (R i) to form the effective weighted bit sequence of G2, and add the effective weighted bit sequence of G2 to the end of G2 to form the shaped G2, and add all EWB (H i ) to form a G3 effective weighted bit sequence, and the G3 effective weighted bit sequence is added to the end of G3 to form the shaped G3, and G1, the shaped G2 and the shaped G3 are parallel-to-serial (P / S) converted to obtain the serial data of the low-power signal.

[0032] As a preferred solution, in step 2, mapping to a 3D-8QAM (3D-8-Quadrature Amplitude Modulation) constellation to obtain a processed low-power signal specifically includes:

[0033] Step 2.2.1: Group the serial data of the low-power signal by 3 bits to obtain groups of the serial data.

[0034] Step 2.2.2: Pair the four groups corresponding to each constellation mapping unit with the thirty-two groups of serial data in sequence, wherein each group corresponds to eight groups of serial data.

[0035] Step 2.2.3: According to the grouping corresponding to the constellation mapping unit, perform constellation mapping according to 3D-8QAM to obtain the constellation coordinate points of the corresponding eight groups of serial data, and so on, to obtain the constellation coordinate points of the thirty-two groups of serial data.

[0036] Step 2.2.4: The constellation coordinate points of the thirty-two groups of string data are used as a constellation mapping unit of string data, and all the constellation mapping units of the string data are used as processed low-power signals.

[0037] As a preferred solution, the step 2.2.3 specifically includes:

[0038] Step 2.2.3.1: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (1, -1, -1).

[0039] Step 2.2.3.2: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of the string data are (-1, -1, 1).

[0040] Step 2.2.3.3: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (-1, 1, 1).

[0041] Step 2.2.3.4: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of string data are (-1, 1, -1).

[0042] Step 2.2.3.5: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 101 in the corresponding group of string data are (-1, 3, -1).

[0043] Step 2.2.3.6: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 001 in the corresponding group of string data are (-1, -3, -1).

[0044] Step 2.2.3.7: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of serial data are (-1, -1, -1).

[0045] Step 2.2.3.8: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (1, 1, -1).

[0046] Step 2.2.3.9: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (-1, -1, -1).

[0047] Step 2.2.3.10: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of string data are (1, -1, 1).

[0048] Step 2.2.3.11: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (1, 1, 1).

[0049] Step 2.2.3.12: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of string data are (1, 1, -1).

[0050] Step 2.2.3.13: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 101 in the corresponding group of string data are (1, 3, -1).

[0051] Step 2.2.3.14: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 001 in the corresponding group of string data are (1, -3, -1).

[0052] Step 2.2.3.15: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of string data are (1, -1, -1).

[0053] Step 2.2.3.16: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (-1, 1, -1).

[0054] Step 2.2.3.17: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (-1, -1, 1).

[0055] Step 2.2.3.18: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 010 in the corresponding group of string data are (1, -1, -1).

[0056] Step 2.2.3.19: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (1, 1, -1).

[0057] Step 2.2.3.20: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of string data are (1, 1, 1).

[0058] Step 2.2.3.21: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 101 in the corresponding group of string data are (1, 3, 1).

[0059] Step 2.2.3.22: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 001 in the corresponding group of string data are (1, -3, 1).

[0060] Step 2.2.3.23: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of string data are (1, -1, 1).

[0061] Step 2.2.3.24: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (-1, 1, 1).

[0062] Step 2.2.3.25: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 000 in the corresponding group of string data are (1, -1, 1).

[0063] Step 2.2.3.26: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 010 in the corresponding group of string data are (-1, -1, -1).

[0064] Step 2.2.3.27: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (-1, 1, -1).

[0065] Step 2.2.3.28: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 111 in the corresponding group of string data are (-1, 1, 1).

[0066] Step 2.2.3.29: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 101 in the corresponding group of string data are (-1, 3, 1).

[0067] Step 2.2.3.30: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 001 in the corresponding group of string data are (-1, -3, 1).

[0068] Step 2.2.3.31: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 011 in the corresponding group of string data are (-1, -1, 1).

[0069] Step 2.2.3.32: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (1, 1, 1).

[0070] As a preferred solution, the step 3 specifically includes:

[0071] Step 3.1: Obtain each constellation mapping unit in the processed high-power signal.

[0072] Step 3.2: Obtain the constellation mapping unit of each serial data in the processed low-power signal.

[0073] Step 3.3: Pair the constellation coordinate points of the four groups in each constellation mapping unit with the constellation coordinate points of the thirty-two groups of string data, and calculate the coordinates of the constellation coordinate points of the PDM superposition of the constellation coordinate points of each group and the constellation coordinate points of the eight groups of string data. The expression of the coordinates of the constellation coordinate points of the PDM superposition is as follows:

[0074]

[0075] Among them, x PDM Indicates the x-axis coordinates of the constellation coordinate points of the PDM superposition, y PDM The y-axis coordinate of the constellation coordinate point superimposed by PDM, PDM Indicates the z-axis coordinate of the constellation coordinate point of PDM superposition, x 1 Indicates the x-axis coordinates of the constellation coordinate points of the group, y 1 The y-axis coordinate of the constellation coordinate point of the group, z 1 The z-axis coordinates of the constellation points representing the grouping, The x-axis coordinate of the constellation coordinate point of the j-th string data group, The y-axis coordinate of the constellation coordinate point of the j-th string data group, Represents the z-axis coordinate of the constellation coordinate point of the j-th group of serial data, where j is an integer from 1 to 8, p1 represents the power proportion of the high-power signal, and p2 represents the power proportion of the low-power signal.

[0076] Step 3.4: Obtain the coordinates of all PDM-superimposed constellation coordinate points as the 3D-32QAM signal after probability shaping.

[0077] In a second aspect, a transmitting end is provided, and the transmitting end is used to execute a three-dimensional low-complexity probability shaping coding method for a PDM optical communication system in the first aspect.

[0078] Beneficial effects: The three-dimensional low-complexity probability shaping coding method for PDM optical communication systems provided by the present invention applies PDM and WDBR-PS technology to three-dimensional constellations. The WDBR technology only needs to operate in the bit dimension and will not increase the hardware burden of the PDM system that is sensitive to resource allocation. At the same time, by extending the two-dimensional constellation to three dimensions, it not only effectively reduces the PAPR of the OFDM signal, but also avoids the problem of sudden increase in bit error rate caused by the small spacing between constellation points in high-order modulation. The present invention achieves high-capacity and high-speed signal transmission while maintaining low complexity.

[0079] Based on the PDM system, the present invention applies the weight-driven bit reversal probability shaping (WDBR-PS) scheme to the three-dimensional constellation. The probability distribution of some bits of the low-power signal at the transmitting end is modified to achieve the effect of probability shaping. The method only needs to perform a reversal operation on some bits of the low-power signal, does not involve complex mathematical calculation processes, and avoids the coding and calculation complexity brought by traditional probability shaping technology. Subsequently, the bit stream adjusted by probability is mapped to the three-dimensional constellation diagram after geometric shaping to complete low-complexity joint shaping. This scheme significantly improves the transmission rate of the signal and improves the bit error rate performance, providing an efficient and low-complexity shaping solution for the PDM system. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 Schematic diagram of the flow of the low-complexity 3D-PS-PDM encoding method.

[0081] Figure 2 Schematic diagram of the probability shaping process based on WDBR.

[0082] Figure 3 Schematic diagram of 3D-PS-PDM constellation overlay.

[0083] Figure 4 Schematic diagram of the experimental device.

[0084] Figure 5 Schematic diagram of bit error rate curve after passing through optical fiber for different 3D-PS-PDM methods. DETAILED DESCRIPTION

[0085] 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.

[0086] The present invention will be further described below in conjunction with specific embodiments.

[0087] Embodiment 1:

[0088] This embodiment introduces a three-dimensional low-complexity probability shaping encoding method for a PDM optical communication system. Figure 1 As shown, the following steps are included:

[0089] Step 1: Perform 3D-QPSK (3D-Quadrature Phase Shift Keying) constellation mapping on the high-power signal (Data1) in the power-multiplexed signal at the transmitting end to obtain a processed high-power signal.

[0090] Step 2: After performing weight-driven bit reversal (WDBR) processing on the low-power signal (Data2) in the power multiplexed signal at the transmitting end, 3D-8QAM (3D-8-Quadrature Amplitude Modulation) constellation mapping is performed to obtain a processed low-power signal.

[0091] Step 3: Perform PDM superposition on the processed high-power signal and the processed low-power signal to obtain a probability-shaped 3D-32QAM (3D-32-Quadrature Amplitude Modulation) signal.

[0092] Step 4: Map the 3D-32QAM signal to each subcarrier in the OFDM system. After completing the subcarrier mapping, use the two-dimensional inverse fast Fourier transform (2D-IFFT) to convert the 3D-OFDM (3D-Orthogonal Frequency Division Multiplexing) signal in the frequency domain into a time domain signal.

[0093] Step 5: Add a cyclic prefix before each 3D-OFDM time domain signal to cope with the inter-symbol interference caused by the multipath effect.

[0094] Furthermore, the expression of the signal after power multiplexing is as follows:

[0095]

[0096] Among them, s represents the signal after power multiplexing, p1 represents the power proportion of the high-power signal, and p2 represents the power proportion of the low-power signal. s1 represents a high-power signal, and s2 represents a low-power signal.

[0097] Furthermore, the step 1 specifically includes:

[0098] Step 1.1: Obtain a high-power signal that accounts for a relatively large proportion of the power in the power-multiplexed signal at the transmitting end.

[0099] Step 1.2: Group the bit stream of the high-power signal into 2-bit groups.

[0100] Step 1.3: Perform constellation mapping on the data in each group according to 3D-QPSK to obtain the constellation coordinate point of each group.

[0101] Step 1.4: The four grouped constellation coordinate points are regarded as a constellation mapping unit, and all the constellation mapping units are regarded as processed high-power signals.

[0102] Furthermore, the step 1.3 specifically includes:

[0103] Step 1.3.1: When the data in the group is 00, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (1, 0, 1).

[0104] Step 1.3.2: When the data in the group is 01, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, 1).

[0105] Step 1.3.3: When the data in the group is 11, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, -1).

[0106] Step 1.3.4: When the data in the group is 10, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, 1).

[0107] Furthermore, the weight-driven bit reversal (WDBR) processing in step 2 is used to utilize the bit reversal operation to amplify the probability of the bit "1" in the sequences G2 and G3 before 3D-8QAM mapping to improve the quality of the transmission signal, such as Figure 2 As shown, specifically including:

[0108] Step 2.1.1: Obtain the low-power signal in the power-multiplexed signal of the transmitter, and divide the M-bit data of the low-power signal into three parallel sequences G1, G2 and G3, where the length of G1 is (3 / 7)M, and the lengths of G2 and G3 are both (2 / 7)M.

[0109] Step 2.1.2: Group the bit streams in groups of k bits each for both G2 and G3, and add an extra bit EWB (R i ), add an extra bit EWB (H) before each bit group of G3 i ), where EWB(R i ) represents the effective weighted bit of the ith group in G2, EWB(Hi ) represents the effective weighted position of the ith group in G3, and k is an integer greater than or equal to 2 as the decision weight.

[0110] Step 2.1.3: In the bit weighted decision process, if the number of "1" in the bit group of G2 or G3 is less than k / 2, the corresponding EWB (R i ) and EWB(H i ) is set to "1", and the data in the bit group of G2 or G3 is bit-reversed. If the number of "1" in the bit group of G2 or G3 is greater than or equal to k / 2, the corresponding EWB (R i ) and EWB(H i ) is set to "0", and the data bits in the bit group of G2 or G3 remain unchanged. As a key step of WDBR, the bit reversal operation is used to amplify the probability of bit "1" in sequences G2 and G3 before 3D-8QAM mapping.

[0111] Step 2.1.4: After the reversal operation is completed, all EWBs (R i ) to form the effective weighted bit sequence of G2, and add the effective weighted bit sequence of G2 to the end of G2 to form the shaped G2, and add all EWB (H i ) to form a G3 effective weighted bit sequence, and the G3 effective weighted bit sequence is added to the end of G3 to form the shaped G3, and G1, the shaped G2 and the shaped G3 are parallel-to-serial (P / S) converted to obtain the serial data of the low-power signal.

[0112] Furthermore, in step 2, mapping to a 3D-8QAM (3D-8-Quadrature Amplitude Modulation) constellation to obtain a processed low-power signal specifically includes:

[0113] Step 2.2.1: Group the serial data of the low-power signal by 3 bits to obtain groups of the serial data.

[0114] Step 2.2.2: Pair the four groups corresponding to each constellation mapping unit with the thirty-two groups of serial data in sequence, wherein each group corresponds to eight groups of serial data.

[0115] Step 2.2.3: According to the grouping corresponding to the constellation mapping unit, perform constellation mapping according to 3D-8QAM to obtain the constellation coordinate points of the corresponding eight groups of serial data, and so on, to obtain the constellation coordinate points of the thirty-two groups of serial data.

[0116] Step 2.2.4: The constellation coordinate points of the thirty-two groups of string data are used as a constellation mapping unit of string data, and all the constellation mapping units of the string data are used as processed low-power signals.

[0117] Furthermore, the step 2.2.3 specifically includes:

[0118] Step 2.2.3.1: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (1, -1, -1).

[0119] Step 2.2.3.2: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of the string data are (-1, -1, 1).

[0120] Step 2.2.3.3: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (-1, 1, 1).

[0121] Step 2.2.3.4: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of string data are (-1, 1, -1).

[0122] Step 2.2.3.5: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 101 in the corresponding group of string data are (-1, 3, -1).

[0123] Step 2.2.3.6: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 001 in the corresponding group of string data are (-1, -3, -1).

[0124] Step 2.2.3.7: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of serial data are (-1, -1, -1).

[0125] Step 2.2.3.8: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (1, 1, -1).

[0126] Step 2.2.3.9: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (-1, -1, -1).

[0127] Step 2.2.3.10: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of string data are (1, -1, 1).

[0128] Step 2.2.3.11: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (1, 1, 1).

[0129] Step 2.2.3.12: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of string data are (1, 1, -1).

[0130] Step 2.2.3.13: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 101 in the corresponding group of string data are (1, 3, -1).

[0131] Step 2.2.3.14: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 001 in the corresponding group of string data are (1, -3, -1).

[0132] Step 2.2.3.15: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of string data are (1, -1, -1).

[0133] Step 2.2.3.16: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (-1, 1, -1).

[0134] Step 2.2.3.17: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (-1, -1, 1).

[0135] Step 2.2.3.18: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 010 in the corresponding group of string data are (1, -1, -1).

[0136] Step 2.2.3.19: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (1, 1, -1).

[0137] Step 2.2.3.20: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of string data are (1, 1, 1).

[0138] Step 2.2.3.21: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 101 in the corresponding group of string data are (1, 3, 1).

[0139] Step 2.2.3.22: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 001 in the corresponding group of string data are (1, -3, 1).

[0140] Step 2.2.3.23: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of string data are (1, -1, 1).

[0141] Step 2.2.3.24: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (-1, 1, 1).

[0142] Step 2.2.3.25: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 000 in the corresponding group of string data are (1, -1, 1).

[0143] Step 2.2.3.26: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 010 in the corresponding group of string data are (-1, -1, -1).

[0144] Step 2.2.3.27: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of string data are (-1, 1, -1).

[0145] Step 2.2.3.28: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 111 in the corresponding group of string data are (-1, 1, 1).

[0146] Step 2.2.3.29: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 101 in the corresponding group of string data are (-1, 3, 1).

[0147] Step 2.2.3.30: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 001 in the corresponding group of string data are (-1, -3, 1).

[0148] Step 2.2.3.31: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 011 in the corresponding group of string data are (-1, -1, 1).

[0149] Step 2.2.3.32: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (1, 1, 1).

[0150] Furthermore, the step 3 specifically includes:

[0151] Step 3.1: Obtain each constellation mapping unit in the processed high-power signal.

[0152] Step 3.2: Obtain the constellation mapping unit of each serial data in the processed low-power signal.

[0153] Step 3.3: Pair the constellation coordinate points of the four groups in each constellation mapping unit with the constellation coordinate points of the thirty-two groups of string data, and calculate the coordinates of the constellation coordinate points of the PDM superposition of the constellation coordinate points of each group and the constellation coordinate points of the eight groups of string data. The expression of the coordinates of the constellation coordinate points of the PDM superposition is as follows:

[0154]

[0155] Among them, x PDM Indicates the x-axis coordinates of the constellation coordinate points of the PDM superposition, y PDM The y-axis coordinate of the constellation coordinate point superimposed by PDM, PDM Indicates the z-axis coordinate of the constellation coordinate point of PDM superposition, x 1 Indicates the x-axis coordinates of the constellation coordinate points of the group, y 1 The y-axis coordinate of the constellation coordinate point of the group, z 1 The z-axis coordinates of the constellation points representing the grouping, The x-axis coordinate of the constellation coordinate point of the j-th string data group, The y-axis coordinate of the constellation coordinate point of the j-th string data group, Represents the z-axis coordinate of the constellation coordinate point of the j-th group of serial data, where j is an integer from 1 to 8, p1 represents the power proportion of the high-power signal, and p2 represents the power proportion of the low-power signal.

[0156] Step 3.4: Obtain the coordinates of all PDM-superimposed constellation coordinate points as the 3D-32QAM signal after probability shaping.

[0157] Embodiment 2:

[0158] This embodiment introduces a transmitting end, which is used to execute a three-dimensional low-complexity probability shaping encoding method for a PDM optical communication system in Embodiment 1.

[0159] Embodiment 3:

[0160] This embodiment introduces a three-dimensional low-complexity probability shaping coding method for PDM optical communication system of the present invention and compares it with the existing coding technology. Figure 3 As shown, Figure 3 The prior art shown in the middle figure a uses conventional 3D-constellation mapping for the high-power signal P1 and the low-power signal P2 to form a QPSK constellation distribution and a rectangular structure constellation distribution respectively. After PDM superposition, the entire constellation diagram presents two 16QAM structures.

[0161] In order to make full use of low power consumption resources, the present invention designs a 3D-PS-PDM2 method, such as Figure 3 As shown in b, the high-power signal P1 still uses QPSK constellation distribution on the XOZ plane of the three-dimensional space, and the low-power signal uses paired mapping P2. The quadrant distribution of the high-power signal determines the mapping rule and constellation distribution of the signal. The mapping rule and three-dimensional constellation coordinates of the present invention are shown in Table 1.

[0162] Table 1 3D-PS-PDM parameters

[0163]

[0164] In the table, xx(a, b, c) indicates that the coordinate distribution of the constellation point of the QPSK symbol 2-bit data xx in three-dimensional space is x=a, y=b, z=c. The four constellation points of the QPSK constellation point are superimposed with the constellation points of the eight mapping schemes corresponding to the low-power signal 8QAM. The superimposed symbol is in the form of 5-bit data xxxxx, the first two bits of the symbol come from the high-power bit stream, and the last three bits come from the low-power signal bit stream. Among them, the four mapping situations of P2 can be simply expressed as:

[0165]

[0166] Among them, x case1 ,y case1 、z case1 Take the three-dimensional coordinates of each constellation point in Example 1. In this way, the constellation distribution of the cube can be expanded outward based on the six faces. This method makes full use of the three-dimensional constellation space. Compared with the traditional two-dimensional square 32QAM, the MED of the constellation point will increase by 17.77%. In order to intuitively show the probability shaping effect of the constellation point, the color depth is used to indicate the probability of symbol occurrence: darker symbols correspond to higher probability of occurrence, and lighter symbols indicate lower probability. It can be clearly seen from the figure that symbols close to the origin of the constellation have a higher probability of occurrence, while the probability of symbols far from the origin is significantly reduced, successfully realizing the probability shaping of the 3D-32QAM constellation.

[0167] Since PDM technology requires precise control of resource allocation, this will bring additional consumption to hardware resources, and the traditional PS solution itself involves a complex calculation process. When the two are used in combination, the complexity of the system and the occupation of hardware resources will be further increased. In response to this problem, the present invention proposes a low-complexity probability shaping scheme suitable for PDM. This technology is only performed at the bit level, without involving higher-level symbols or signal amplitudes, and effective probability shaping can be achieved by adjusting the probability distribution of low-power bits in the transmitter. This method simplifies the complex calculation process, and the final output is a group of bits converted from the input data source, which can be seamlessly integrated into the subsequent bit-level processing flow, avoiding the coding and calculation complexity problems brought about by traditional probability shaping technology when applied to PDM.

[0168] Embodiment 4:

[0169] This embodiment introduces the application of the method of the present invention in a 3D-PS-PDM transmission system based on intensity modulation-direct detection (IMDD). Figure 4As shown in the figure, at the optical line terminal (OLT), the 3D-PS-PDM signal is first generated by an offline DSP. The generated signal is distributed to 240 subcarriers, and the 512-point IFFT converts the frequency domain signal into a time domain signal. 240 3D32QAM signals are used, 10 of which are used for channel equalization. A CP (cyclic prefix) of 1 / 16 of the OFDM (optical orthogonal frequency division multiplexing) symbol is added to each symbol as a guard band. Then the digital-to-analog conversion is completed by an arbitrary waveform generator, and the generated electrical signal is amplified by an electrical amplifier and injected into a Mach-Zehnder modulator for photoelectric modulation, and then optically amplified by an erbium-doped fiber amplifier. After being transmitted in a 25km single-mode optical fiber, the signal is distributed to different optical network units (ONUs) through a power divider. A variable optical attenuator is set in front of each ONU to adjust the signal attenuation to adapt to different transmission conditions. The received optical signal is converted into an electrical signal by a photodetector and captured using a mixed signal oscilloscope with a sampling rate of 50GSa / s, and finally demodulated by 3D-PS-PDM in an offline DSP.

[0170] Figure 5 The figure shows the variation of the bit error rate of the two 3D-PS-PDM schemes with the received optical power under different optical power conditions. The prior art 3D-PS-PDM1 and the present invention 3D-PS-PDM2 use different constellation mapping methods. The bit error rate shown in the figure is the average of the high-power signal and the low-power signal. The results show that 3D-PS-PDM2 has higher receiving sensitivity than 3D-PS-PDM1. At the same bit error rate of 3.8×10 -3 Under the condition of , 3D-PS-PDM2 achieves a gain of about 0.4 dB. This further proves that the PDM2 method used in the present invention can significantly improve the system gain compared with PDM1.

[0171] 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 three-dimensional low-complexity probability shaping coding method for PDM optical communication system, characterized by: The steps include: Step 1: Perform 3D-QPSK constellation mapping on the high-power signal in the power multiplexed signal of the transmitting end to obtain a processed high-power signal; Step 2: After performing weight-driven bit inversion processing on the low-power signal in the power multiplexed signal at the transmitting end, 3D-8QAM constellation mapping is performed to obtain a processed low-power signal; Step 3: Perform PDM superposition on the processed high-power signal and the processed low-power signal to obtain a probability-shaped 3D-32QAM signal; Step 4: Map the 3D-32QAM signal to each subcarrier in the OFDM system. After completing the subcarrier mapping, use the inverse frequency domain transform to convert the 3D-OFDM signal in the frequency domain into a time domain signal; Step 5: Add a cyclic prefix before each 3D-OFDM time domain signal to obtain the added 3D-OFDM time domain.

2. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 1, characterized in that: The expression of the signal after power multiplexing is as follows: Among them, s represents the signal after power multiplexing, p1 represents the power proportion of the high-power signal, and p2 represents the power proportion of the low-power signal. s1 represents a high-power signal, and s2 represents a low-power signal.

3. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 1, characterized in that: The step 1 specifically includes: Step 1.1: Obtain a high-power signal that accounts for a relatively large proportion of the power in the power-multiplexed signal at the transmitting end; Step 1.2: Group the bit stream of the high-power signal into 2-bit groups; Step 1.3: Perform constellation mapping on the data in each group according to 3D-QPSK to obtain the constellation coordinate point of each group; Step 1.4: The four grouped constellation coordinate points are regarded as a constellation mapping unit, and all the constellation mapping units are regarded as processed high-power signals.

4. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 3 is characterized in that: The step 1.3 specifically includes: Step 1.3.1: When the data in the group is 00, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (1,0,1); Step 1.3.2: When the data in the group is 01, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, 1); Step 1.3.3: When the data in the group is 11, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, -1); Step 1.3.4: When the data in the group is 10, according to the constellation mapping rule of 3D-QPSK, the coordinates of the constellation coordinate point of the group are (-1, 0, 1).

5. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 1, characterized in that: The weight-driven bit inversion process in step 2 specifically includes: Step 2.1.1: Obtain the low-power signal in the power-multiplexed signal of the transmitting end, and divide the M-bit data of the low-power signal into three parallel sequences G1, G2 and G3; wherein the length of G1 is (3 / 7)M, and the lengths of G2 and G3 are both (2 / 7)M; Step 2.1.2: Group the bit streams in groups of k bits each for both G2 and G3, and add an extra bit EWB (R i ), add an extra bit EWB (H) before each bit group of G3 i ), where EWB(R i ) represents the effective weighted bit of the ith group in G2, EWB(H i ) represents the effective weighted position of the ith group in G3, and k is an integer greater than or equal to 2; Step 2.1.3: In the bit weighted decision process, if the number of "1"s in the bit group of G2 or G3 is less than k / 2, the corresponding EWB (R i ) and EWB(H i ) is set to "1", and the data in the bit group of G2 or G3 is bit-reversed; if the number of "1" in the bit group of G2 or G3 is greater than or equal to k / 2, the corresponding EWB (R i ) and EWB(H i ) is set to "0", and the data bits in the bit group of G2 or G3 remain unchanged; Step 2.1.4: After the reversal operation is completed, all EWBs (R i ) to form the effective weighted bit sequence of G2, and add the effective weighted bit sequence of G2 to the end of G2 to form the shaped G2, and add all EWB (H i ) to form a G3 effective weighted bit sequence, and the G3 effective weighted bit sequence is added to the end of G3 to form the shaped G3, and G1, the shaped G2 and the shaped G3 are parallel-to-serial (P / S) converted to obtain the serial data of the low-power signal.

6. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 5, characterized in that: The mapping to the 3D-8QAM constellation in step 2 to obtain a processed low-power signal specifically includes: Step 2.2.1: grouping the serial data of the low-power signal in a 3-bit manner to obtain a grouping of the serial data; Step 2.2.2: Pair the four groups corresponding to each constellation mapping unit with the thirty-two groups of serial data in sequence, wherein each group corresponds to eight groups of serial data; Step 2.2.3: According to the grouping corresponding to the constellation mapping unit, constellation mapping is performed according to 3D-8QAM to obtain the constellation coordinate points of the corresponding eight groups of serial data, and so on to obtain the constellation coordinate points of the groups of thirty-two serial data; Step 2.2.4: The constellation coordinate points of the thirty-two groups of string data are used as a constellation mapping unit of string data, and all the constellation mapping units of the string data are used as processed low-power signals.

7. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 6, characterized in that: The step 2.2.3 specifically includes: Step 2.2.3.1: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of string data are (1, -1, -1); Step 2.2.3.2: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of the string data are (-1, -1, 1); Step 2.2.3.3: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of the string data are (-1, 1, 1); Step 2.2.3.4: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of the string data are (-1, 1, -1); Step 2.2.3.5: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 101 in the corresponding group of the string data are (-1, 3, -1); Step 2.2.3.6: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 001 in the corresponding group of the string data are (-1, -3, -1); Step 2.2.3.7: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of the string data are (-1, -1, -1); Step 2.2.3.8: When the data in the group is 00, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of the string data are (1, 1, -1); Step 2.2.3.9: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of the string data are (-1, -1, -1); Step 2.2.3.10: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of the string data are (1, -1, 1); Step 2.2.3.11: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of the string data are (1, 1, 1); Step 2.2.3.12: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of the string data are (1, 1, -1); Step 2.2.3.13: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 101 in the corresponding group of the string data are (1, 3, -1); Step 2.2.3.14: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 001 in the corresponding group of the string data are (1, -3, -1); Step 2.2.3.15: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of the string data are (1, -1, -1); Step 2.2.3.16: When the data in the group is 01, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of the string data are (-1, 1, -1); Step 2.2.3.17: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 000 in the corresponding group of the string data are (-1, -1, 1); Step 2.2.3.18: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of the string data are (1, -1, -1); Step 2.2.3.19: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of the string data are (1, 1, -1); Step 2.2.3.20: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of the string data are (1, 1, 1); Step 2.2.3.21: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 101 in the corresponding group of the string data are (1, 3, 1); Step 2.2.3.22: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 001 in the corresponding group of string data are (1, -3, 1); Step 2.2.3.23: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of the string data are (1, -1, 1); Step 2.2.3.24: When the data in the group is 11, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of the string data are (-1, 1, 1); Step 2.2.3.25: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 000 in the corresponding group of string data are (1, -1, 1); Step 2.2.3.26: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 010 in the corresponding group of the string data are (-1, -1, -1); Step 2.2.3.27: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 110 in the corresponding group of the string data are (-1, 1, -1); Step 2.2.3.28: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 111 in the corresponding group of the string data are (-1, 1, 1); Step 2.2.3.29: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 101 in the corresponding group of the string data are (-1, 3, 1); Step 2.2.3.30: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of data 001 in the corresponding group of string data are (-1, -3, 1); Step 2.2.3.31: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 011 in the corresponding group of the string data are (-1, -1, 1); Step 2.2.3.32: When the data in the group is 10, according to the constellation mapping rule of 3D-8QAM, the coordinates of the constellation coordinate point of the data 100 in the corresponding group of string data are (1, 1, 1).

8. The three-dimensional low-complexity probability shaping coding method for PDM optical communication system according to claim 1, characterized in that: The step 3 specifically includes: Step 3.1: Obtain each constellation mapping unit in the processed high-power signal; Step 3.2: Obtain a constellation mapping unit of each string data in the processed low-power signal; Step 3.3: Pair the constellation coordinate points of the four groups in each constellation mapping unit with the constellation coordinate points of the thirty-two groups of string data, and calculate the coordinates of the constellation coordinate points of the PDM superposition of the constellation coordinate points of each group and the constellation coordinate points of the eight groups of string data; wherein the expression of the coordinates of the constellation coordinate points of the PDM superposition is as follows: Among them, x PDM Indicates the x-axis coordinates of the constellation coordinate points of the PDM superposition, y PDM The y-axis coordinate of the constellation coordinate point of PDM superposition, z PDM Indicates the z-axis coordinate of the constellation coordinate point of PDM superposition, x 1 Indicates the x-axis coordinates of the constellation coordinate points of the group, y 1 The y-axis coordinate of the constellation coordinate point of the group, z 1 The z-axis coordinates of the constellation points representing the grouping, The x-axis coordinate of the constellation coordinate point of the j-th string data group, The y-axis coordinate of the constellation coordinate point of the j-th string data group, The z-axis coordinate of the constellation coordinate point of the j-th string data group, where j is an integer from 1 to 8, p1 represents the power proportion of the high-power signal, and p2 represents the power proportion of the low-power signal; Step 3.4: Obtain the coordinates of all PDM-superimposed constellation coordinate points as the 3D-32QAM signal after probability shaping.

9. A transmitting end, characterized in that: The transmitting end is used to execute a three-dimensional low-complexity probability shaping encoding method for a PDM optical communication system as claimed in any one of claims 1 to 8.

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