LDPC Channel Encoding with Modulation-Aware Shortening Patterns
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current LDPC codes used in communication systems, such as DVB-S2, are limited to only two codeword lengths, which restricts their extendibility and flexibility, especially in high-order modulation schemes like 16-QAM, 64-QAM, and 256-QAM, where bit reliabilities differ, necessitating a method to generate LDPC codes with various codeword lengths without requiring new parity-check matrices.
Innovation Solution
The method involves using shortening or puncturing techniques on existing LDPC codes, specifically optimizing shortening and puncturing patterns based on the modulation scheme to generate LDPC codewords with varying lengths, ensuring optimal performance by considering the degree distribution and cycle characteristics of the Tanner graph.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LDPC codes are designed with fixed codeword lengths (e.g., 16200 and 64800), then the code structure is simplified and easier to implement, but the adaptability to different data rates and modulation schemes is limited
Solution Approach 1:
The LDPC code is divided into information bits and parity bits, with the parity bits further segmented into puncturable sections. This segmentation allows flexible shortening and puncturing to achieve different code rates while maintaining the base code structure, thus resolving the contradiction between structural simplicity and adaptability.
Solution Approach 2:
The patent introduces dynamic shortening and puncturing patterns that can be adjusted based on the required code rate and modulation scheme. The shortening pattern determines which information bits are set to zero, while the puncturing pattern determines which parity bits are not transmitted, allowing the system to adapt to different data rates without changing the base code structure.
2Reliability
If new parity-check matrices are designed for each codeword length to optimize performance, then the error correction capability is improved, but the system complexity and memory requirements increase
Solution Approach 1:
A single base parity-check matrix H1 is designed to support multiple codeword lengths (16200 and 64800) through shortening and puncturing techniques. This universal matrix structure eliminates the need for separate optimized matrices for each code length, reducing system complexity while maintaining good error correction performance through pattern-based adaptation.
Solution Approach 2:
Instead of changing the parity-check matrix structure for different codeword lengths, the patent changes parameters such as the shortening pattern (which information bits are zeroed) and puncturing pattern (which parity bits are removed). These parameter changes allow the same matrix to produce different effective codes with varying performance characteristics suitable for different modulation schemes.
3Reliability
If shortening and puncturing patterns are optimized for each modulation scheme, then the performance in high-order modulation is improved, but the complexity of pattern selection and implementation increases
Solution Approach 1:
The patent applies different shortening and puncturing patterns to different sections of the code based on the modulation scheme. For example, in high-order modulation where bit reliability varies, certain information bits are selectively shortened or punctured based on their position and reliability characteristics. This local optimization improves performance without requiring complete redesign for each modulation scheme.
Solution Approach 2:
The shortening and puncturing patterns are pre-determined and stored for different modulation schemes and code rates. During operation, the appropriate pattern is selected based on the current transmission conditions, avoiding real-time optimization complexity. The patterns are designed in advance to account for the reliability characteristics of different modulation schemes.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A method and apparatus for encoding and decoding a channel in a communication system using a Low-Density Parity-Check (LDPC) code. The encoding method includes determining a modulation scheme for transmitting a symbol; determining a shortening pattern in consideration of the determined modulation scheme; grouping columns corresponding to an information word in a parity-check matrix of the LDPC code into a plurality of column groups; ordering the column groups; determining a range of a resulting information word desired to be obtained by shortening the information word; based on the range of the resulting information word, performing column group-by-column group shortening on the ordered column groups of the information word, according to the determined shortening pattern; and LDPC-encoding the shortened information word.