LDPC Channel Coding with Modulation-Aware Shortening Patterns
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Solution Overview
Problem
Current LDPC code 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
A channel encoding/decoding method and apparatus that uses shortening or puncturing patterns tailored to high-order modulation schemes, allowing for the generation of LDPC codes with different codeword lengths by grouping and ordering columns in the parity-check matrix, and applying specific shortening or puncturing techniques based on the modulation scheme to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LDPC code systems use fixed parity-check matrices for specific codeword lengths (e.g., DVB-S2 with 16200 and 64800), then the system achieves reliable error correction performance, but the system loses flexibility and extendibility to support various codeword lengths
Solution Approach 1:
The parity-check matrix is divided into column groups that can be selectively used. By grouping columns and applying shortening patterns to specific groups, the system can generate different codeword lengths from a single base matrix, resolving the contradiction between versatility and complexity
Solution Approach 2:
The system dynamically selects and applies different shortening patterns based on the desired codeword length and modulation scheme. This dynamic adaptation allows a single fixed parity-check matrix to serve multiple codeword length requirements, eliminating the need for multiple static matrices
2Adaptability or versatility
If the system stores multiple parity-check matrices for different codeword lengths, then it can support various code rates and lengths, but memory efficiency decreases and system complexity increases
Solution Approach 1:
A single parity-check matrix is designed to serve multiple functions by supporting various codeword lengths through column group shortening. This universal matrix replaces the need for multiple specialized matrices, reducing memory requirements while maintaining adaptability
Solution Approach 2:
The system changes parameters (shortening patterns, column group selections) rather than changing the fundamental parity-check matrix structure. This allows different code rates and lengths to be achieved by modifying operational parameters rather than storing multiple complete matrices
3Reliability
If shortening patterns are not optimized for high-order modulation schemes, then the system maintains simplicity, but reliability decreases in 16-QAM, 64-QAM, and 256-QAM scenarios
Solution Approach 1:
Different shortening patterns are applied to different column groups based on their specific reliability characteristics in high-order modulation schemes. This local optimization ensures that bits mapped to less reliable modulation positions receive appropriate shortening treatment, improving overall reliability without requiring complete redesign
Data Source
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.