LDPC Bit Permutation for QAM Mapping Under QEF SNR Limits
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Solution Overview
Problem
The existing methods for processing digital audio and video signals, particularly in second-generation digital terrestrial television broadcasting, do not adequately improve the signal-to-noise ratio (SNR) required for quasi error-free (QEF) conditions when using LDPC codes with QAM modulations such as 16 QAM, 64 QAM, and 256 QAM.
Innovation Solution
The proposed solution involves specific permutation schemes in the 'Demux' block to improve the association between LDPC encoder output bits and constellation coordinates for QAM modulations, employing an interleaver structure similar to the DVB-S2 standard, with different permutation methods for various QAM modulation levels and code rates, ensuring better bit association and signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the standard DVB-S2 interleaver structure is used with QAM modulations, then the system maintains compatibility with existing standards and implementation simplicity, but the signal-to-noise ratio performance is insufficient to achieve quasi error-free conditions
Solution Approach 1:
The interleaver is divided into multiple sub-interleavers, each handling a portion of the encoded bits. This segmentation allows optimization of bit-to-constellation mapping for different QAM modulations (16-QAM, 64-QAM, 256-QAM) while maintaining the overall interleaver structure compatible with DVB-S2 standards.
Solution Approach 2:
Different permutation schemes are applied to different subsets of bits within the encoded packet. Specifically, bits associated with different constellation coordinates (I and Q components) undergo different permutation treatments to optimize their respective error performance characteristics for each QAM modulation type.
2Reliability
If LDPC codes are used with QAM modulations in digital terrestrial television broadcasting, then broadband transmission capability is achieved, but the association between encoded bits and constellation coordinates is insufficient for optimal performance
Solution Approach 1:
Bit permutation is performed in advance during the interleaving stage, before modulation. The permutation schemes are specifically designed to pre-arrange bits in optimal positions for subsequent QAM mapping, ensuring that bits most susceptible to errors are placed in constellation coordinates with better error resilience.
Solution Approach 2:
Different permutation parameters and schemes are selected based on the specific QAM modulation type being used. The system adapts the interleaving parameters (such as permutation patterns and sub-interleaver configurations) to match the characteristics of 16-QAM, 64-QAM, or 256-QAM modulations for optimal performance.
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.