LDPC Interleaver Permutation for QAM Constellation Bit Association
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Solution Overview
Problem
The existing LDPC encoding schemes used in second-generation digital terrestrial television broadcasting, when associated with QAM modulations, do not provide a satisfactory signal-to-noise ratio for achieving the Quasi Error Free condition, particularly with 16QAM, 64QAM, and 256QAM modulations.
Innovation Solution
The proposed method improves the association between LDPC encoder output bits and QAM constellation coordinates by employing specific permutation schemes in the interleaver and mapper blocks, tailored for different code rates and modulation levels, using an interleaver structure similar to the DVB-S2 standard, to optimize bit association and constellation mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the standard LDPC encoding scheme with QAM modulation is used, then the system complexity is maintained at acceptable levels, but the signal-to-noise ratio performance is insufficient to achieve Quasi Error Free condition
Solution Approach 1:
The encoded bit stream is divided into multiple groups that are separately permuted and mapped to different constellation coordinates. This segmentation allows optimization of each group's mapping to improve overall SNR performance while keeping individual mapping operations manageable in complexity
Solution Approach 2:
Different permutation and mapping strategies are applied to different portions of the bit stream based on their importance and the specific QAM constellation being used. This local optimization ensures that critical bits are mapped to more robust constellation positions, improving reliability without uniformly increasing complexity across the entire system
2Reliability
If the interleaver structure from DVB-S2 standard is used, then the implementation simplicity is maintained, but the association between LDPC encoder output bits and QAM constellation coordinates is not optimized
Solution Approach 1:
The bit permutation and mapping scheme is pre-configured and optimized for specific QAM constellations (16QAM, 64QAM, 256QAM) and code rates. This preliminary optimization allows the system to achieve better bit association without requiring complex real-time decision-making, thereby improving reliability while controlling implementation complexity
Solution Approach 2:
The permutation and mapping parameters are specifically tailored to match the characteristics of different QAM constellations and LDPC code rates. By adjusting these parameters according to the specific transmission conditions, the system optimizes the association between encoder output and constellation coordinates without requiring a complete redesign of the interleaver structure
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 a LDPC code with a 3/5 code rate, in combination with a QAM modulation, for example the 16QAM or 64QAM or 256QAM 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.