Error correction coding and probability shaping method applied to short distance optical fiber communication

Abstract

The application relates to an error correction coding and probability shaping method applied to short-distance optical fiber communication, which comprises the following steps: firstly coding source information based on a hard decision ladder code, and secondly coding the source information after the first coding based on a soft decision Hamming code; dividing the source information after the second coding, and the divided source information will be subjected to probability shaping based on an enumeration sphere mapping or be used for high-order modulation. The beneficial effect of the application is that the technical scheme can adopt a probability shaping technology to adjust the probability of symbol appearance and reduce the average power of a signal. The maximum capacity of a communication channel can be realized by optimizing the probability distribution of a source, the probability shaping technology is a method for improving the information transmission rate by adopting a source distribution other than a uniform distribution under the constraint of limited average power, and the probability shaping technology can guarantee the communication reliability while reducing the transmission power of a transmitter.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication, specifically to the field of channel coding, and particularly to an error correction coding and probabilistic shaping method for short-distance optical fiber communication. Background Technology

[0002] With the exponential growth of global information data, the technological development of high-speed optical fiber communication must keep pace with the demands of users in this field, making data center optical interconnects a global research hotspot, with high-speed, short-distance data centers being the focus. Finding a channel coding scheme that achieves higher information rates and the lowest possible transmission frequency is currently a key research challenge. According to Shannon's theorem, reliable communication data and high transmission rates are mutually exclusive. Existing technologies, such as joint coding and modulation schemes combining probabilistic shaping techniques with high-speed optical fiber communication channel coding, result in lower average power of the shaped symbols while ensuring information accuracy and reliability. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an error correction coding and probabilistic shaping method for short-distance optical fiber communication. In the coding process, it adopts a sequence of forward error correction coding followed by probabilistic shaping to ensure communication reliability while reducing the transmitter's transmission power and energy consumption.

[0004] An error correction coding and probabilistic shaping method for short-distance optical fiber communication includes the following steps:

[0005] The source information is first encoded using hard-decision ladder code, and the first encoded source information is then encoded a second time using soft-decision Hamming code.

[0006] The source information after the second encoding is divided, and the divided source information will be probabilistically shaped based on the enumerated ball mapping or used for higher-order modulation.

[0007] Furthermore, the step of performing probability shaping based on the enumerated ball mapping includes:

[0008] The second encoded source information u c Divided into symbolic information u a And plastic surgery information u s u s After being mapped based on enumerated spheres, the distribution is mapped to an amplitude sequence of a preset length.

[0009] Furthermore, the formula for probabilistic shaping based on enumerated ball mapping includes:

[0010]

[0011] k′ is the number of bits that can be mapped from the set of shaped sequences S0 determined by the energy amplitude lattice;

[0012] Contains k s The information sequence of bits u s Mapped to a length of amplitude sequence;

[0013] Before performing astrological mapping, you need to... a The amplitude sequence after equal distribution and shaping;

[0014] Where M represents the modulation order, such as M=4 for 16QAM modulation.

[0015] Furthermore, the step of performing the first encoding based on the hard-decision ladder code includes:

[0016] The hard decision code is constructed as a ladder code, the ladder code is a BCH code with a code length of 2n, the length of the parity check bit of the ladder code is k, and the length of the information codeword of the ladder code is 2n-k.

[0017] Choose an n×n matrix Bi (i = 0, 1, 2, ...), with the left nk columns forming the information bits and the right k columns forming the check bits, and so on, following the matrix structure described above.

[0018] Beneficial effects of the invention

[0019] The technical solution of this invention adopts a sequence of forward error correction coding followed by probabilistic shaping in the coding process, and can use probabilistic shaping technology to adjust the probability of symbol occurrence and reduce the average power of the signal. The maximum capacity of the communication channel can be achieved by optimizing the probability distribution of the information source. Under the constraint of finite average power, probabilistic shaping technology uses a source distribution other than uniform distribution to improve the information transmission rate, ensuring communication reliability while reducing the transmitter's transmission power. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0021] Figure 1 This is a flowchart of the encoding and modulation process at the transmitting end according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of a ladder code according to an embodiment of the present invention;

[0023] Figure 3This is a schematic diagram of an example of a ladder code according to an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of an amplitude lattice structure according to an embodiment of the present invention;

[0025] Figure 5 This is a schematic diagram of the debugging result of one embodiment of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present invention will become clearer and more apparent.

[0027] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0028] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] This invention provides an error correction coding and probabilistic shaping method for short-distance optical fiber communication. This scheme combines echelon codes and an enumerated ball mapping algorithm, and adopts a sequence of forward error correction coding followed by probabilistic shaping in the coding process. It has three main advantages: First, by changing the rate of the amplitude shaping block in the fixed forward error correction (FEC) code, the transmission rate of the Probabilistic Shaping (PS) scheme can be easily adjusted, making the proposed scheme more universal. Second, since the decoding of the FEC code precedes the deshaping operation in the PS, the requirement for a potentially complex soft-output deshaper is eliminated, simplifying the matching relationship between the transmitted information and the symbol information required for shaping in the system. Third, by maintaining the probability distribution unchanged, the bit error rate is further reduced, and performance is improved.

[0030] The main design parameters of this design scheme include: the length N of the shaped sequence, and the maximum energy E of the shaped sequence. max Amplitude sequence A = {a1, a2, ...}, integer coding rate R s Step code rate R HD Hamming code rate R SD .

[0031] The main coding and modulation process of this scheme includes: ladder code coding, Hamming code coding, shaping, and modulation. The transmitting end coding and modulation flowchart is shown below. Figure 1As shown. In this scheme, the source information is first subjected to forward error correction coding, and the encoded information u c It will be divided into two parts, one of which is of length k without any operation. a The information sequence of bits u a The length to be shaped is k s The information sequence of bits u s The distribution matcher will uniformly distribute u s This is mapped to an amplitude sequence with a target distribution. And the information u... a The symbols used as constellation points, together with the amplitude sequence, are used to form constellation points according to the 16QAM mapping rules before being transmitted into the optical fiber.

[0032] This scheme first performs two forward error correction codes on the source data. The first coding is hard-decision, aimed at reducing coding complexity, and the second coding is soft-decision, aimed at reducing the bit error rate. The hard-decision coding used in this invention is constructed using a ladder code, which combines the ideas of convolutional coding and block coding. The ladder code selects a BCH code with a code length of 2n as the component code, and the parity check bit length is k, so the information codeword length is 2n-k. An n×n matrix Bi (i=0,1,2,…) is selected, with the left nk columns forming the information bits and the right k columns forming the parity bits. The initial matrix B0 is set as an all-zero matrix, as shown below. Figure 2 As shown, taking a ladder code consisting of five code blocks as an example, each code block is concatenated in a ladder manner to form the ladder code. The gray part represents the parity bit. Matrix Each row is a valid codeword of the BCH, meaning that each row and column of the ladder block is a valid codeword of the BCH. The soft-decision encoding method uses Hamming codes to further ensure the accuracy of the information.

[0033] The overhead introduced by forward error correction coding follows a uniform distribution. To ensure that the integer distribution remains unchanged, this scheme will encode the information u... c Divided into symbolic information u a And plastic surgery information u s u s After passing through a distribution matcher based on enumerated sphere mapping, binary information is mapped into an amplitude sequence of a certain length. At the same shaping rate, enumerated sphere mapping exhibits lower rate loss than constant-component distribution matching; therefore, this scheme uses an algorithm based on enumerated sphere mapping for the probabilistic shaping part to meet the requirements of high-speed optical communication. s The mapping relationship with the amplitude sequence is determined by the bounded energy amplitude lattice of the enumerated sphere mapping. Figure 4As shown, taking an amplitude lattice structure as an example, in this structure, each state represents an energy level, each branch represents an amplitude in the amplitude set A = {a1, a2, ...}, and each path from the zero-energy state to the last state represents an amplitude sequence. In the figure, n represents the number of columns in the amplitude lattice structure; l represents the number of rows in the amplitude lattice structure; and e represents the cumulative energy of the amplitude sequence of the previous n states. This represents the total number of paths from the current energy state to the last energy state, therefore This represents the total number of sequences in the structure. In a joint coding scheme, only the set of sequences whose number is a power of 2 can establish a one-to-one mapping with the source information; therefore, some sequences need to be discarded.

[0034] The maximum number of bits that can be mapped from the set of shaped sequences S0 determined by the energy amplitude lattice is...

[0035]

[0036] In summary, containing k s The information sequence of bits u s Mapped to a length of amplitude sequence.

[0037] Before performing astrological mapping, you need to... a The evenly distributed amplitude sequence requires k a and k s The following relationship must be satisfied:

[0038]

[0039] Where M represents the modulation order, such as M=4 for 16QAM modulation.

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following description uses an 800Gbit / s short-range optical communication system with DP-16QAM modulation as an example, with reference to the accompanying drawings. This embodiment is implemented based on the design method of this application, but is not limited to this transmission system. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0041] To reduce system computational load, the batch size (i.e., the number of repetitions) is set to 6868. The parameters for this example are designed as follows: integer sequence length N = 16, maximum integer sequence energy E... max =72, amplitude sequence A={1,3}, integer coding rate Ladder code rate Hamming code rate The solution process is as follows:

[0042] The information is divided into two paths, I and Q, and the same processing is performed on both paths.

[0043] Taking the I-channel as an example, the source information (326,757,852,652 bits) is subjected to ladder coding, where the code rates of the ladder codes are R. HD and R SD Ladder coding will incur overhead u OH The initial matrix B0 is set to a 512×512 matrix of all zeros. Then B1 is 512×510. The left 478 columns of B1 are used as information bits, and the right 32 columns are parity bits. Subsequent ladder blocks are constructed similarly to block B1, and so on. Each row of matrix [BT i-1, Bi] exactly satisfies the selected component code BCH (1022, 990). However, a problem arises during ladder construction: since the blocks after B1 are not constructed as m×m matrices, they cannot be directly pieced together, resulting in a 2-column error. Therefore, the solution is to add a 512×2 matrix of all zeros after encoding B1 and the subsequent matrices, forming a 512×512 square matrix. This allows for ladder combination using the traditional ladder encoding method. Figure 3 As shown, the light gray area represents the parity bit, and the dark gray area represents the added 512×2 all-zero matrix. Regarding the coding efficiency of the ladder code, the coding efficiency of the ladder code constructed from the component code BCH(1022,990) is... The codewords encoded using the echelon code are then encoded using Hamming code to further ensure the accuracy of the information. The Hamming code has a code rate of [missing information]. Information u after forward error correction coding c The length is 375,000,046,080 bits.

[0044] To complete the constellation mapping, u c It is divided into two parts, where u s (175,000,021,504 bits) are fed into the main matcher for probability shaping, u a (200,000,024,576 bits) are reserved as symbols for constellation points.

[0045] For u s Perform distribution matching. Design the probability amplitude shape with the following parameters: Let the length of the integer sequence N = 16, the maximum sequence energy Emax = 72, and when the set of integer amplitudes A = {1, 3}, the total number of possible sequences can be calculated by enumeration. The sequence was divided into 2^14 groups, with the lowest energy being used for shaping. Therefore, the shaping coding rate Rs = 14 / 16 = 0.8750. The shaped constellation diagram is shown below. Figure 5As shown. After shaping, the probability of amplitude "1" is 0.6691, the probability of amplitude "3" is 0.3309, and the average energy of the constellation diagram is 3.6472. After shaping, u s The length is exactly the same as u a It remains consistent and conforms to the mapping rules of 16QAM modulation.

[0046] Furthermore, this also includes constellation mapping. The specific mapping rules for the I-path are shown in the table below, and the same applies to the Q-path.

[0047] 00 +1 01 +3 10 -1 11 -3

[0048] This example uses a joint coding and modulation process of probabilistic shaping and forward error correction to transmit 326,757,852,652 bits of data through probabilistic shaping and forward error correction, introducing additional shaping and check information. Ultimately, this results in 400,000,049,152 bits of data entering the fiber optic channel in 16QAM modulation format. The total code rate of this implementation example is approximately 0.81689.

[0049] The final modulation mapping result is as follows Figure 5 As shown.

[0050] The flowcharts and block diagrams in the foregoing figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the figures. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented by a dedicated hardware-based system that performs the specified function or operation, or by a combination of dedicated hardware and computer instructions.

[0051] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0053] The present invention has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present invention based on these embodiments, all of which fall within the scope of protection of the present invention.

Claims

1. A method for error correction coding and probabilistic shaping applied to short-distance optical fiber communication, characterized in that the steps include... The method comprises the following steps: Firstly, source information is encoded based on a hard decision step code, and then the first encoded source information is secondly encoded based on a soft decision Hamming code; The secondly encoded source information is divided, and the divided source information is subjected to probability shaping based on an enumeration sphere mapping or used for high-order modulation; The probability shaping based on the enumeration sphere mapping comprises the following formula: The second encoded source information u c is divided into sign information u a and shaping information u s , u s is mapped into an amplitude sequence of a preset length after distribution based on enumeration sphere mapping. To accomplish constellation mapping, u c is split into two parts, where u s is sent to the local matcher for probability shaping, and u a is left as the sign of the constellation point for later use; u s Distribution matching is performed, and the probability amplitude shape is designed according to the following parameters: let the shaping sequence length N = 16, the maximum sequence energy Emax = 72, and when the shaping amplitude set A = {1, 3}, a total of 214 groups of sequences can be generated by enumeration operation The sequence, wherein the energy of the 214 groups of sequences is the lowest, is applied to shaping, and thus the shaping coding rate Rs = 14 / 16 = 0.8750; after shaping, the probability of the amplitude "1" appearing is 0.6691, the probability of the amplitude "3" appearing is 0.3309, and the average energy of the constellation diagram is 3.6472; after shaping, the length of u s is consistent with that of u a , and the mapping rule of 16QAM modulation is met.

2. The error correction coding and probability shaping method for short haul optical fiber communication according to claim 1, wherein, k′ is the number of bits that a shaping sequence set S0 determined by an energy amplitude grid can establish mapping, and N is the length of the shaping sequence. Wherein, M represents the modulation order. contains k s bits of information sequence u s is mapped to an amplitude sequence of length n. Before constellation mapping, u a is equally distributed to the shaped amplitude sequence; The first encoding based on the hard decision step code comprises the following steps:

3. The method for error correction coding and probability shaping for short haul optical fiber communications according to claim 1, wherein, The hard decision encoding is a step code, the code length of the step code is a BCH code of 2n, the parity check bit length of the step code is k, and the information code word length of the step code is 2n-k; An n×n matrix Bi is selected, wherein i=0, 1, 2, …, the left n-k columns constitute information bits, and the right k columns constitute check bits, and the above matrix structure is analogized. ​

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