LDPC Bit Demultiplexer Layout for Multi-Level Modulation
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Solution Overview
Problem
Existing cable television transmission systems face challenges in achieving efficient error correction due to the complexity and cost of random bit interleaving in multi-level modulation environments, which affects spectral and power efficiency.
Innovation Solution
A bit demultiplexer is designed to partition LDPC coded bits uniformly and map them to different levels of the constellation mapper, modeling non-uniform parallel channels using surrogate binary erasure channels to reduce complexity and improve error correction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If random bit interleaving is used to match irregular code profile to multi-level modulation, then error correction performance is improved, but device complexity and implementation cost increase substantially
Solution Approach 1:
The patent segments the coded bitstream into multiple groups and distributes them to different modulation levels in a systematic manner. Instead of random interleaving across the entire bitstream, the system divides the code blocks into groups and assigns each group to specific constellation levels, reducing the complexity of memory access patterns and circuit routing while maintaining the matching between code profile and modulation characteristics.
Solution Approach 2:
The patent changes the parameter of bit distribution from random to systematic based on code block groups. By modifying the interleaving parameter from completely random to group-based systematic distribution, the system achieves a balance between performance and complexity, where the group structure provides regularity that simplifies implementation while still achieving good error correction performance through level-specific mapping.
2Reliability
If random bit interleaver is inserted between channel encoder and constellation mapper, then spectral efficiency is improved, but productivity for high-speed implementation decreases
Solution Approach 1:
The patent segments the bitstream processing into code block groups that can be handled independently and in parallel. This segmentation enables high-speed implementation by allowing multiple groups to be processed simultaneously through parallel processing paths, while still achieving spectral efficiency through the systematic distribution of groups to different modulation levels.
Solution Approach 2:
The patent performs preliminary grouping of code blocks into structured groups before the interleaving stage. This preliminary organization creates a regular pattern that simplifies subsequent processing and enables more efficient high-speed implementation, as the grouping structure is established in advance and can be processed through systematic mapping rather than requiring complex real-time random access.
3Reliability
If traditional interleaving methods are used, then error correction is provided, but power efficiency decreases
Solution Approach 1:
The patent changes the fundamental parameter of bit distribution from random to systematic group-based mapping. This parameter change reduces the computational complexity of the interleaving operation, leading to fewer processing cycles and lower power consumption while maintaining effective error correction through the structured distribution of code blocks to modulation levels.
Data Source
AI summary
A method involves receiving an LDPC coded bitstream and demultiplexing the received LDPC coded bitstream using an optimized demultiplexer, the optimized demultiplexer being designed by:substituting Q levels of a constellation mapper by Q parallel binary erasure channels;optimizing a density evolution of erasure probability over said binary erasure channels for a plurality of demultiplexer offsets; andidentifying from the plurality of demultiplexer offsets those with a minimum number of check node decoder collisions.