Rate-Compatible LDPC Coding for H-ARQ With Constant Block Size
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Solution Overview
Problem
Current rate-compatible low-density parity-check (LDPC) codes for hybrid automatic repeat request (H-ARQ) applications face challenges in maintaining constant information block size and high degrees of punctured variable nodes, making them unsuitable for high-throughput communications.
Innovation Solution
The method involves generating low-rate protographs from high-rate protographs by copying, permuting, and pruning systematic input nodes and edges, and puncturing codeword bits using regular-irregular, random, or progressive node puncturing to achieve desired code rates, ensuring flexible and efficient rate adaptation in noisy channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If rate-compatible LDPC codes are used for H-ARQ applications, then flexibility in adapting to different data rates is improved, but the information block size cannot be kept constant and the degrees of punctured variable nodes become insufficient
Solution Approach 1:
The code is divided into information bits and parity bits with fixed segmentation. The information block size remains constant while only the parity bits are extended or punctured to achieve different code rates, maintaining structural consistency across different rates
Solution Approach 2:
A single parent LDPC code structure serves multiple code rates through systematic puncturing and extension operations. The same base graph and parity check matrix can generate codes at different rates by selectively transmitting information and parity bits, providing universal functionality across varying channel conditions
2Productivity
If high-rate codes are generated by puncturing lower-rate codes, then higher data rates are achieved, but the degrees of punctured variable nodes become high making implementation complex
Solution Approach 1:
The parent LDPC code is designed in advance with predetermined puncturing patterns and positions. The parity check matrix and base graph are constructed beforehand to facilitate systematic puncturing operations, avoiding complex real-time decisions during encoding
Solution Approach 2:
Different regions of the code structure are treated differently: information bits maintain fixed positions while parity bits are subject to selective puncturing. The puncturing operation focuses locally on specific parity bit positions rather than uniformly affecting all bits, simplifying the overall implementation
Data Source
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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 where the puncturing pattern will be as regular as possible with respect to the preceding code, random puncturing, or progressive node puncturing to obtain a desired code from a preceding code.