LDPC Substream Decoding for Higher-Order Constellation Mapping
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Solution Overview
Problem
Low-density parity-check (LDPC) coding does not provide optimal coding performance when used with higher order modulation constellation mapping, such as 16-QAM, 64-QAM, and 256-QAM, due to the relationship between symbol reliability and error protection in digital television signal transmission systems like DVB-T and DVB-H.
Innovation Solution
A method and apparatus that de-map modulation symbols into separate substreams, decode each substream using LDPC coding at different rates, and combine them into a single data stream, employing parallel non-binary LDPC coding and tailored symbol mapping to address the inequity in bit reliability within higher order constellation maps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LDPC coding is used with higher order modulation constellation mapping (16-QAM, 64-QAM, 256-QAM), then data transmission rate and bandwidth efficiency are improved, but coding performance deteriorates due to inequity in bit reliability within the constellation map
Solution Approach 1:
The patent segments the bit positions within the modulation constellation into multiple groups based on their reliability characteristics. Different LDPC coding rates are applied to different groups of bits, with more reliable bit positions (typically those farther from the constellation center) receiving lower coding rates and less reliable bit positions (closer to the center) receiving higher coding rates. This segmentation allows the system to optimize coding performance for each bit group while maintaining high data transmission rates.
Solution Approach 2:
The patent applies local quality by assigning different coding rates to different spatial locations within the constellation map. Specifically, bits mapped to certain regions of the constellation (e.g., inner vs. outer regions, or specific bit positions within symbols) receive differentiated error protection levels. This localized differentiation of coding quality matches the local reliability characteristics of each bit position, thereby improving overall coding performance without sacrificing transmission rate.
2Productivity
If higher order modulation constellation mapping is used, then bandwidth efficiency is improved, but error correction capability deteriorates due to reduced symbol reliability
Solution Approach 1:
The patent changes the coding rate parameter dynamically based on the modulation order and bit position reliability. For higher order modulations (16-QAM, 64-QAM, 256-QAM), the system employs variable coding rates across different bit groups rather than a uniform coding rate. This parameter change allows the system to adapt the error correction strength to match the reduced symbol reliability inherent in higher order modulations, thereby maintaining error correction capability while preserving bandwidth efficiency.
3Device complexity
If uniform LDPC coding rate is applied to all bits in higher order modulation, then device complexity is reduced, but coding performance deteriorates due to ignoring bit reliability differences
Solution Approach 1:
The patent segments the data stream into multiple substreams corresponding to different bit positions within the modulation symbols. Each substream is then encoded with a different LDPC coding rate appropriate to its reliability characteristics. This segmentation approach achieves good coding performance by accounting for bit reliability differences while maintaining relatively simple device complexity through the use of standard LDPC encoding structures applied to separate substreams.
Data Source
AI summary
Modern coding and modulation techniques have greatly improved the transmission and reception of signals. A method is described including receiving a signal de-mapping the signal into a first and second substream, decoding the first and second substream using a low density parity check decoding process, and combining the first and second decoded substream into a single data stream. An apparatus is described including a symbol de-mapper that receives a signal de-maps the modulation symbols in the signal into a first and second substream, a first decoder that decodes the first substream using a low density parity check coding process at a first decoding rate, a second decoder that decodes the second substream at a second encoding rate, and a combiner that combines the first substream and the second substream into a single data stream.