LDPC Bit Interleaving for QAM Mapping Under SNR Constraints
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Solution Overview
Problem
The existing LDPC encoding schemes used in digital terrestrial television broadcasting, when associated with QAM modulations, do not adequately meet the signal-to-noise ratio (SNR) requirements for achieving quasi error-free conditions, particularly for 16 QAM, 64 QAM, and 256 QAM modulations.
Innovation Solution
The proposed solution involves specific permutation schemes in the Demux block to improve the association between LDPC encoder output bits and QAM constellation coordinates, employing an interleaver structure similar to the DVB-S2 standard, with different permutation methods for various QAM modulations and code rates, ensuring optimal bit association and signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LDPC encoding is used with QAM modulations in digital terrestrial television broadcasting, then the data transmission capability is improved, but the signal-to-noise ratio requirement increases making it difficult to achieve quasi error-free conditions
Solution Approach 1:
The encoded bit stream is divided into groups of N bits (where N=4 for 16-QAM, N=6 for 64-QAM, N=8 for 256-QAM) and processed through an interleaver that permutes these groups. This segmentation allows optimal association between LDPC codewords and modulation symbols, improving error correction performance while maintaining high data transmission capability
Solution Approach 2:
An intermediary interleaver structure is introduced between the LDPC encoder and the QAM mapper. This interleaver performs permutation on groups of N bits according to specific patterns (e.g., y0=b0, y1=bN-1, y2=b1, y3=bN-2 for 16-QAM) to optimize the mapping relationship, thereby achieving quasi error-free performance without sacrificing transmission capability
2Productivity
If standard interleaving is used between LDPC encoder and constellation mapper, then the encoding efficiency is maintained, but the association between encoded bits and constellation coordinates is suboptimal for QAM modulations
Solution Approach 1:
Different permutation patterns are applied locally according to the specific QAM modulation type. For 16-QAM, a specific permutation pattern is used; for 64-QAM, another pattern is applied; and for 256-QAM, yet another pattern is used. This local optimization ensures optimal bit-to-constellation-point association for each modulation scheme while maintaining encoding efficiency
Solution Approach 2:
The interleaver parameters (number of columns M, number of rows L, and permutation patterns) are changed according to the code rate and modulation type. For example, different parameters are used for code rates 1/3, 2/5, 3/5, and different QAM modulations, allowing precise optimization of bit association for each specific configuration
Data Source
AI summary
Methods for digital signal processing and transmission/reception systems utilizing the methods based on the use of LDPC codes, for example the LDPC code with a 3/5 code rate, in combination with a QAM modulation, for example the 16 QAM or 64 QAM or 256 QAM modulation. In transmission, a bit permutation (Demux) is carried out prior to the QAM constellation mapping function, and in reception, the bit permutation is carried out after the QAM constellation demapping function.