LDPC Bit Interleaving for Reliable High-Order QAM Modulation
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Solution Overview
Problem
Existing wireless communication systems face challenges in maintaining high spectral efficiency, energy efficiency, latency, and reliability, particularly in scenarios with limited channel rank and fading channels, where high order modulations like super QAM reduce the minimum Euclidean distance of the constellation.
Innovation Solution
The implementation of an interleaver mechanism that re-orders LDPC coded bits, associating high-degree encoded bits with most significant bits and low-degree encoded bits with least significant bits of constellation symbols, combined with Gray-Labeled Quadrature Amplitude Modulation (QAM), to enhance the error correction capabilities of quasi-cyclic LDPC codes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high order modulations like super QAM are used to increase spectral efficiency, then spectral efficiency is improved, but the minimum Euclidean distance of the constellation is reduced, worsening reliability
Solution Approach 1:
The patent applies local quality by differentiating the treatment of encoded bits based on their degree. High-degree encoded bits are mapped to most significant bits (MSBs) of constellation symbols, while low-degree encoded bits are mapped to least significant bits (LSBs). This non-uniform mapping strategy protects more critical bits (high-degree) with greater robustness, thereby improving reliability without sacrificing spectral efficiency.
2Reliability
If an interleaver mechanism is implemented to re-order encoded bits and protect high-degree variable nodes, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-calculating and storing the degree distribution of the LDPC code before encoding. The interleaver is configured with this degree distribution information in advance, allowing it to systematically re-order encoded bits according to their degrees without requiring complex real-time calculations during transmission, thus managing complexity while improving reliability.
3Reliability
If Gray-Labeled QAM is used with re-ordered encoded bits to enhance error correction, then reliability is improved, but processing complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the mapping between encoded bits and constellation symbols. Instead of using conventional uniform mapping, the system uses degree-based non-uniform mapping where the position and significance of each bit in the constellation symbol are determined by the degree of the corresponding encoded bit. This parameter change enhances decoder performance while keeping the modulation scheme itself (Gray-Labeled QAM) relatively simple.
Data Source
AI summary
Various aspects of the present disclosure relate to techniques for interleaved low-density parity-check (LDPC) modulations. An apparatus is configured to encode data using a LDPC code to generate a stream of encoded bits, associate each encoded bit of the stream of encoded bits with most significant bits and least significant bits of one or more constellation symbols based on a degree of each of the encoded bits, generate a stream of re-ordered encoded bits, wherein a first set of encoded bits associated with the most significant bits have a higher degree than a second set of encoded bits associated with the least significant bits, perform Gray-Labeled Quadrature Amplitude Modulation (QAM) on the stream of re-ordered encoded bits to generate one or more modulation symbols, and transmit the one or more modulation symbols.