BICM Bit Mapping With Outer BCH for 256QAM LDPC Reception
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Solution Overview
Problem
The reception performance of a receiver can be improved by optimizing the permutation rules applied to LDPC codeword bits prior to mapping, specifically for LDPC codes and constellations used by the transmitter and receiver, to enhance the association between bits and constellation symbols.
Innovation Solution
A Bit-Interleaved Coding Modulation (BICM) encoding method that optimizes permutation rules for LDPC codeword bits before mapping, utilizing a BICM encoder with a BCH encoder and LDPC encoder, and a bit-to-cell demultiplexer to rearrange bits into cell words suitable for QAM constellations, improving the association between LDPC codeword bits and constellation symbols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bit-interleaving and demultiplexing is used, then the system is compatible with standard modulation schemes, but reception performance is suboptimal for specific LDPC codes and constellations
Solution Approach 1:
The patent applies different permutation rules tailored to specific combinations of LDPC codes and QAM constellations. Instead of using a universal permutation rule, the system selects optimized permutation patterns based on the specific code rate and modulation order being used, thereby improving reception performance for each specific configuration.
Solution Approach 2:
The patent changes the parameters of the permutation rules based on the LDPC code rate and QAM constellation order. Different code rates (e.g., 1/2, 2/3, 3/4) and modulation orders (e.g., 16QAM, 64QAM, 256QAM) have associated optimized permutation patterns that are selected dynamically, allowing the system to adapt to different operating conditions for optimal performance.
2Reliability
If optimized permutation rules are applied, then error correction performance improves, but the complexity of the encoding and decoding process increases
Solution Approach 1:
The patent applies bit permutation to the LDPC codeword bits before they are input to the mapper. This preliminary rearrangement of bits ensures that the most significant bits and least significant bits are optimally positioned for the subsequent modulation process, improving error correction performance without adding complexity during the actual modulation and demodulation operations.
Solution Approach 2:
The patent introduces an intermediary permutation step between the LDPC encoding and QAM modulation processes. This intermediate bit reordering acts as a mediator that optimizes the interface between the error correction code and the modulation scheme, allowing both to work together more effectively without requiring fundamental changes to either component.
3Reliability
If bit permutation is applied before mapping, then the association between bits and constellation symbols is improved, but additional processing steps are required
Solution Approach 1:
The patent combines the bit permutation operation with the existing demultiplexing function in the BICM encoder. By integrating the permutation step into the standard demultiplexing process, the system improves bit-constellation association without requiring completely separate processing stages, thereby minimizing the impact on data processing efficiency.
Data Source
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AI summary
Information bits are encoded according to an outer BCH code (111) and an inner low density parity check code (115) with code rate 7/15 and a codeword length of 16200. The resulting codeword bits are bit-interleaved (120) and the interleaved bits are demultiplexed (130) into 8 sequences of bits. The 8 sequences of bits are permuted (130) according to a predetermined permutation rule: v0 = b2, v1 = b6, v2 = b0, v3 = b1, v4 = b4, v5 = b5, v6 = b3, v7 = b7 and mapped onto symbols of a 256 QAM constellation (140).