Rate-Compatible LDPC Coding With Protograph Pruning and Puncturing
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Solution Overview
Problem
Existing rate-compatible low-density-parity check (LDPC) codes for hybrid automatic repeat request (H-ARQ) applications have issues with variable information block size and high degrees of punctured nodes, making them unsuitable for high-rate applications.
Innovation Solution
The method involves generating low-rate protographs from high-rate protographs by copying, permuting, and pruning systematic input nodes and edges, and using puncturing techniques such as regular-irregular, random, and progressive node puncturing to achieve desired code rates, ensuring low degrees of punctured variable nodes and efficient rate adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If existing rate-compatible LDPC codes are used for H-ARQ applications, then error correction capability is provided, but variable information block size and high degrees of punctured nodes make them unsuitable for high-rate applications
Solution Approach 1:
The code is segmented into information bits and parity bits with fixed block sizes. The encoder processes fixed-size blocks through systematic encoding, separating information and parity components. This segmentation enables fixed-rate operation while maintaining error correction capability, resolving the contradiction between high transmission rate and code structure complexity.
Solution Approach 2:
The code parameters are optimized with specific design rates (1/2, 2/3, 3/4) and fixed block sizes. By changing and fixing these parameters rather than using variable rates, the system achieves high throughput while maintaining manageable code structure complexity suitable for H-ARQ applications.
2Productivity
If puncturing techniques are used to achieve higher code rates, then data transmission rate increases, but high degrees of punctured nodes reduce decoding efficiency
Solution Approach 1:
Parity bits are extracted and punctured systematically from the encoded block to achieve desired code rates. By removing only the parity portion while keeping information bits intact, the system increases transmission rate while maintaining low node degrees in the Tanner graph, preserving decoding efficiency.
Solution Approach 2:
Different parts of the codeword are treated differently: information bits are preserved while parity bits are punctured. This local differentiation allows rate adaptation without uniformly increasing node degrees, maintaining decoding efficiency at various code rates.
3Adaptability or versatility
If variable block sizes are used to accommodate different data amounts, then flexibility for rate adaptation is improved, but implementation complexity increases
Solution Approach 1:
A single encoder design with fixed block size serves multiple code rates (1/2, 2/3, 3/4) through systematic puncturing of parity bits. This universal encoder structure eliminates the need for multiple variable-size encoders, reducing implementation complexity while maintaining rate adaptation flexibility.
Solution Approach 2:
The system achieves dynamic rate adaptation not through variable block sizes but through selective puncturing of parity bits. The encoder dynamically adjusts the transmitted code rate by controlling which parity bits are punctured, maintaining fixed block size structure while providing rate flexibility.
Data Source
AI summary
In one embodiment, the present patent application comprises a method and apparatus to generate low rate protographs from high rate protographs, comprising copying a base graph; permuting end points of edges of a same type in copies of the base graph to produce a permuted graph; and pruning systematic input nodes in the permuted graph and the edges connected to them. In another embodiment, the present patent application comprises a method and apparatus to generate high-rate codes from low-rate codes, comprising puncturing a subset of codeword bits, wherein the step of puncturing a subset of codeword bits comprises regular-irregular puncturing the subset of codeword bits, random puncturing variable nodes, or progressive node puncturing variable nodes to obtain a desired code from a preceding code.