A Probabilistic Shaping Four-Dimensional Coded Modulation Method

Abstract

The present invention relates to a probabilistic shaping four-dimensional coding modulation method, comprising the following steps: S1, preprocessing an original binary data sequence to obtain a two-dimensional coding matrix, and setting preset values ​​for coding check bits and coding flag bits in partitions; S2, bit-flipping the two-dimensional coding matrix based on a flipping rule, resetting the coding flag bits, obtaining a flipped two-dimensional coding matrix, and adjusting a shaping degree factor to achieve a specific probability distribution; S3, performing diversity setting coding on the adjusted two-dimensional coding matrix, resetting the coding check bits, and dividing the transmission constellation corresponding to the flipped two-dimensional coding matrix into multiple sets to obtain a diversity two-dimensional coding matrix; S4, using the columns of the diversity two-dimensional coding matrix as basic units, re-parallel-to-serial conversion is performed to restore the transmission data sequence, and mapping it into transmission symbols. Compared with the existing technology, the present invention has the advantages of low complexity.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber communication, and in particular to a probability shaping four-dimensional coding modulation method. Background Art

[0002] With the continuous emergence and vigorous development of emerging Internet services such as virtual reality and augmented reality, global Internet traffic has experienced a spurt in growth. As the primary carrier of data communication backbone networks, fiber-optic communications, with their increased transmission bandwidth and capacity, have played a vital role in driving the development of the data communication era. Polarization multiplexing technology fully utilizes the high-dimensional degrees of freedom of light to transmit information across multiple polarization states of light, exponentially increasing the transmission capacity of optical communication systems. However, polarization-dependent signal impairments such as inter-polarization crosstalk and polarization-independent loss severely restrict the performance of polarization-multiplexed transmission systems, significantly hindering capacity and rate increases. Since multiple dimensions of light in optical polarization-multiplexed communication systems carry valid information, high-dimensional coding, by introducing parity bits in the encoding process to generate multi-dimensional connections, improves the energy efficiency of optical polarization-multiplexed transmission systems and has become an important technical means to overcome existing bottlenecks.

[0003] Four-dimensional modulation coding is an excellent high-dimensional modulation technology. It encodes the two orthogonal polarization states of light (X polarization state and Y polarization state) and the orthogonal components (I phase and Q phase) in each polarization state based on a partitioning strategy to effectively increase the minimum Euclidean distance between signal constellation points. At the same time, probability shaping technology adjusts the probability of occurrence of each constellation point to conform to the rule that the greater the symbol energy, the lower the probability of occurrence, reducing the average energy of the transmitted symbol to reduce the nonlinear damage to the transmission system. Therefore, the probability-shaped four-dimensional modulated signal can fully utilize the high-dimensional degrees of freedom of light while achieving flexible transmission by adjusting the source entropy, thereby improving transmission performance. However, commonly used distribution matchers used to implement specific probability distributions, including constant composition distribution matchers, often require greater implementation complexity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a low-complexity probability shaping four-dimensional coding modulation method.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A probability shaping four-dimensional coding modulation method comprises the following steps:

[0007] S1. Preprocess the original binary data sequence to obtain a two-dimensional coding matrix, and set the preset values ​​of the coding check bit and the coding flag bit in each partition, wherein the preset value is 0;

[0008] S2. Based on the flipping rule, the two-dimensional coding matrix is ​​bit-flipped and the coding flag is reset to obtain the flipped two-dimensional coding matrix, and the shaping degree factor is adjusted to achieve a specific probability distribution;

[0009] S3, performing diversity setting coding on the adjusted two-dimensional coding matrix, resetting the coding check bit, and dividing the transmission constellation corresponding to the flipped two-dimensional coding matrix into multiple sets to obtain a two-dimensional coding matrix after diversity setting;

[0010] S4. Using the columns of the two-dimensional coding matrix after diversity as basic units, re-parallel-to-serial conversion is performed to restore the transmission data sequence, and mapped into transmission symbols based on mapping rules.

[0011] Furthermore, the preprocessing is specifically as follows: truncating the original binary data sequence to obtain an input bit sequence having a length equal to the number of taps, performing a serial-to-parallel conversion on the input bit sequence to obtain a two-dimensional coding matrix.

[0012] Furthermore, the number of taps is calculated based on a shaping degree factor.

[0013] Furthermore, for a 16QAM signal, the two-dimensional coding matrix has a total of 4 rows.

[0014] Furthermore, for a 16QAM signal, performing bit flipping on the two-dimensional coding matrix specifically involves performing bit flipping on the first two rows of the two-dimensional coding matrix.

[0015] Furthermore, for 16QAM signals, the flipping rule is: determining whether to perform bit flipping based on the relative number of 0 and 1 bits in a single row of bits.

[0016] Furthermore, the determination of whether to perform bit flipping based on the relative number of 0 and 1 bits in a single row of bits is specifically as follows: if the number of 0 bits in a single row is greater than the number of 1 bits, the original bit state is maintained; conversely, if the number of 0 bits in a single row is less than the number of 1 bits, the original bits in the row are flipped.

[0017] Furthermore, the encoding flag is reset as follows: when the original bit state is maintained, an encoding flag 0 is added at the end of a single line; when the original bits in the line are flipped, an encoding flag 1 is added at the end of the line.

[0018] Furthermore, the mapping into transmission symbols specifically includes mapping odd columns in the two-dimensional coding matrix after diversity into X polarization state transmission symbols, and mapping even columns into Y polarization state transmission symbols.

[0019] Furthermore, the mapping rule satisfies the condition that the code distance between adjacent constellation points is minimum.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The main operations of the bit flip coding and partition setting coding in the present invention are simple bit-level operations including bit flip operations. These operations are friendly to hardware implementation, have low complexity, require few hardware resources, and have physical implementation advantages.

[0022] (2) The coding modulation method adopted by the present invention realizes the generation of a specific McWell-Boltzmann probability distribution signal to improve the signal-to-noise ratio tolerance of the transmission system, taking into account the requirements of the transmission method for effectiveness and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the present invention;

[0024] Figure 2 This is a schematic diagram showing the principle of implementing the partition setting coding of the present invention;

[0025] Figure 3 This is the symbol mapping rule diagram of the present invention. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0027] Example 1:

[0028] The present invention provides a probability shaping four-dimensional coding modulation method, the flow chart of the method is as follows Figure 1 The method comprises the following steps:

[0029] S1. Preprocess the original binary data sequence to obtain a two-dimensional coding matrix, and set preset values ​​of the coding check bit and the coding flag bit in partitions, where the preset value is 0.

[0030] The specific steps of S1 are:

[0031] Get the original binary data sequence x, intercept the original binary data sequence x, and obtain a length equal to the number of taps n b The input bit sequence is converted from serial to parallel to obtain a two-dimensional coding matrix.

[0032] Taking into account the channel conditions of the actual transmission system, the number of taps n for diversity interception is d for:

[0033] n b =(k+1)*4(k+1) / 2-2

[0034] Among them, k is the shaping degree factor.

[0035] Input bit sequence x in for:

[0036] x in =[x(1),x(2),…,x(n b )]

[0037] Taking 16QAM signal encoding as an example, the input bit sequence x in Performing serial-to-parallel conversion, the obtained two-dimensional encoding matrix is:

[0038]

[0039] The length and width of the matrix are l and m respectively.

[0040] m=4,l=k+1

[0041] The coding matrix of 16QAM signal coding has 4 rows and k+1 columns, with a total of n b Information bits, (k-1) / 2 partition setting code check bits and 2 bit flip coding flag bits. During data preprocessing, the partition setting code check bits and the bit flip coding flag bits are preset to 0.

[0042] At this time, considering the newly added coding redundancy bits, the coding efficiency η is:

[0043]

[0044] S2. Based on the flipping rule, the two-dimensional coding matrix is ​​bit-flipped and the coding flag is reset to obtain the flipped two-dimensional coding matrix, and the shaping degree factor is adjusted to achieve a specific probability distribution.

[0045] The specific steps of S2 are:

[0046] The probability of occurrence of each constellation point in a probabilistically shaped signal is not equally distributed, as with conventional modulation formats. Instead, it varies with the energy value of each signal, following the principle that the greater the signal energy, the lower the probability of occurrence. Obviously, this probability distribution reduces the source information entropy, reducing the net transmission rate at the same symbol baud rate. However, this probability distribution reduces the distribution of high-energy symbols, thereby reducing nonlinear transmission impairments caused by high transmission power in optical communication transmission systems. Furthermore, the adjustable and continuous change of source entropy significantly benefits the flexibility of optical transmission systems.

[0047] Bit flipping will change the distribution probability of 0 and 1 bits in the two-dimensional coding matrix where 0 and 1 bits are originally equally distributed, so as to map the transmission symbols with a specific probability distribution.

[0048] Taking the 16QAM modulated signal as an example, the bits in the first two rows of the two-dimensional coding matrix are flipped based on the flipping rule to achieve a specific probability distribution. The expression for bit flipping is:

[0049]

[0050]

[0051] As can be seen from the above formula, the flipping rule determines whether to perform bit flipping based on the relative number of 0 and 1 bits within a row. If there are more 0 bits than 1 bits in a row, the original bit state is maintained. Conversely, if there are fewer 0 bits than 1 bits in a row, the original bits in the row are flipped.

[0052] The encoding flags are reset as follows: when a bit is flipped, a coding flag of 0 is added to the end of a row to maintain the original bit state; when the original bits within a row are flipped, a coding flag of 1 is added to the end of the row. The resulting flipped two-dimensional encoding matrix is ​​obtained. After bit-flip encoding, there will be more 0 bits in the first two rows. Since the first two rows represent the first two bits of the binary representation of each transmitted symbol, 00xx has the highest probability of occurring among all binary representations of transmitted symbols, followed by 01xx and 10xx. The least likely occurrence is 11xx.

[0053] For the flipped two-dimensional coding matrix, a specific probability distribution is achieved by adjusting the shaping factor k.

[0054] S3. Perform diversity setting coding on the adjusted two-dimensional coding matrix, reset the coding check bit, and divide the transmission constellation diagram corresponding to the flipped two-dimensional coding matrix into multiple sets to obtain a two-dimensional coding matrix after diversity setting.

[0055] Optical four-dimensional modulation utilizes orthogonal polarization degrees of freedom and orthogonal components to jointly modulate signals. Diversity coding adds parity bits (coded parity bits) to the two polarization transmission data, dividing the original transmission constellation into multiple sets to achieve optical four-dimensional modulation.

[0056] Taking SP128QAM as an example, the principle of diversity setting encoding is as follows Figure 2 shown.

[0057] The expression of the principle is:

[0058]

[0059] S4. Using the columns of the two-dimensional coding matrix after diversity as basic units, re-parallel-to-serial conversion is performed to restore the transmission data sequence, and mapped into transmission symbols based on mapping rules.

[0060] After the diversity setup is complete, the two-dimensional coding matrix is ​​re-parallel-to-serial converted, using columns as the basic unit, to restore the transmission data sequence and map it into transmission symbols. Odd-numbered columns in the two-dimensional coding matrix are mapped into X-polarization state transmission symbols, while even-numbered columns are mapped into Y-polarization state transmission symbols for polarization multiplexing system transmission, completing coded modulation.

[0061] Due to the existence of bit flip coding, it is necessary to map the bit sequence with higher probability into the symbol with lower energy. At the same time, the mapping rule needs to meet the condition of minimum code distance between adjacent constellation points. The symbol mapping rule is as follows: Figure 3 As shown in Figure 2. A bitwise XOR operation is used in the mapping process.

[0062] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A probability shaping four-dimensional coding modulation method, characterized in that: The following steps are involved: S1. Preprocess the original binary data sequence to obtain a two-dimensional coding matrix, and set the preset values ​​of the coding check bit and the coding flag bit in each partition, wherein the preset value is 0; S2. Based on the flipping rule, the two-dimensional coding matrix is ​​bit-flipped and the coding flag is reset to obtain the flipped two-dimensional coding matrix, and the shaping degree factor is adjusted to achieve a specific probability distribution; S3, performing diversity setting coding on the adjusted two-dimensional coding matrix, resetting the coding check bit, and dividing the transmission constellation corresponding to the flipped two-dimensional coding matrix into multiple sets to obtain a two-dimensional coding matrix after diversity setting; S4, using the columns of the two-dimensional coding matrix after diversity as basic units, re-parallel-to-serial conversion is performed to restore the transmission data sequence, and mapped into transmission symbols based on a mapping rule; The preprocessing specifically includes: intercepting the original binary data sequence to obtain an input bit sequence with a length equal to the number of taps, performing a serial-to-parallel conversion on the input bit sequence to obtain a two-dimensional coding matrix; The number of taps for diversity interception n b for: n b =(k+1)*4-(k+1) / 2-2 Among them, k is the shaping degree factor; The mapping into transmission symbols is specifically as follows: mapping the odd columns in the two-dimensional coding matrix after diversity into X polarization state transmission symbols, and mapping the even columns into Y polarization state transmission symbols; The mapping rule satisfies the condition that the code distance between adjacent constellation points is minimum.

2. A probabilistic shaping four-dimensional coding modulation method according to claim 1, characterized in that: The number of taps is calculated based on a shaping degree factor.

3. The method for probabilistic shaping four-dimensional coding modulation according to claim 1, wherein: For a 16QAM signal, the two-dimensional coding matrix has 4 rows in total.

4. The method for probabilistic shaping four-dimensional coding modulation according to claim 3, wherein: For a 16QAM signal, performing bit flipping on the two-dimensional coding matrix specifically involves flipping the bits of the first two rows of the two-dimensional coding matrix.

5. The method for probabilistic shaping four-dimensional coding modulation according to claim 3, wherein: For a 16QAM signal, the flipping rule is: whether to perform bit flipping is determined based on the relative number of 0 and 1 bits in a single row of bits.

6. A probabilistic shaping four-dimensional coding modulation method according to claim 5, characterized in that: The determination of whether to perform bit flipping based on the relative number of 0 and 1 bits in a single row of bits is specifically as follows: if the number of 0 bits in a single row is greater than the number of 1 bits, the original bit state is maintained; conversely, if the number of 0 bits in a single row is less than the number of 1 bits, the original bits in the row are flipped.

7. A probabilistic shaping four-dimensional coding modulation method according to claim 6, characterized in that: Reset the encoding flag to: when keeping the original bit state, add the encoding flag 0 at the end of a single line; when flipping the original bits in the line, add the encoding flag 1 at the end of the line.

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