QC-LDPC Bit Mapping With Cyclic Permutation for Non-Uniform QAM
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Solution Overview
Problem
Existing bit-interleaved coding and modulation (BICM) systems using quasi-cyclic low-density parity-check (QC LDPC) codes and quadrature amplitude modulation (QAM) do not optimize the mapping of LDPC codeword bits to QAM constellation bits, leading to suboptimal performance due to varying importance levels of bits and robustness levels of constellation points.
Innovation Solution
Implement a cyclic block permutation and non-uniform constellation selection based on the code rate of QC LDPC codes, combined with a bit interleaver to match the importance levels of LDPC codeword bits with the robustness levels of QAM constellation points, optimizing the mapping process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard uniform constellation mapping is used in BICM systems with QC LDPC codes, then the system structure remains simple, but the communication performance is suboptimal due to mismatch between bit importance levels and constellation robustness levels
Solution Approach 1:
The patent applies local quality by introducing non-uniform constellation points with different robustness characteristics to match the local importance levels of different bit positions in the LDPC codeword. Specifically, bits with higher importance (affecting more codeword bits) are mapped to more robust constellation points, while less important bits are mapped to less robust points, creating a localized optimization at each bit position.
Solution Approach 2:
The patent changes the parameter of constellation uniformity from uniform to non-uniform, creating constellation points with varying distances from the origin. This parameter change allows different bits to be mapped to constellation points with appropriate robustness levels, improving the overall mapping efficiency and communication performance.
2Reliability
If cyclic block permutation is implemented to optimize bit-to-constellation mapping, then bit error rates are reduced, but the processing complexity increases
Solution Approach 1:
The patent segments the LDPC codeword into N cyclic blocks, each containing Q bits. This segmentation allows independent permutation processing of each block while maintaining the overall structure. The cyclic block permutation operates on these segmented blocks, reducing the complexity compared to permuting all bits individually while still achieving the desired mapping optimization.
Solution Approach 2:
The patent performs cyclic block permutation as a preliminary action before the actual constellation mapping. By pre-arranging the bits into cyclic blocks and determining their permutation order in advance, the system prepares the optimal mapping configuration before transmission, which simplifies the real-time processing during communication while achieving reduced bit error rates.
Data Source
AI summary
A communication method includes executing a cyclic block permutation for a codeword generated based on a quasi-cyclic parity-check code including a repeat-accumulate quasi-cyclic low-density parity-check code, where the cyclic block permutation is permutation of cyclic blocks within the codeword, and mapping each bit of the codeword for which the cyclic block permutation is executed to any one of constellation point of a non-uniform constellation.