Protograph LDPC Coding for Adaptive High-Order Modulation
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Solution Overview
Problem
Existing methods for designing low-density parity-check (LDPC) codes often focus on specific modulation schemes and rates, limiting their adaptability and efficiency in supporting multiple modulation levels and rates, particularly in bit-interleaved coded modulation (BICM) systems.
Innovation Solution
The development of a general protograph-based BICM framework that calculates iterative decoding thresholds for higher-order modulations, allowing for multiple rates and adaptive modulation, using a two-stage lifting approach and the PEXIT algorithm to achieve thresholds close to the BICM capacity limit across a wide range of rates and modulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If existing LDPC code design methods focus on specific modulation schemes and rates, then the code design is simplified and optimized for that specific case, but the adaptability to support multiple modulation levels and rates is limited
Solution Approach 1:
The patent applies universality by designing a protograph-based LDPC code construction method that can accommodate multiple modulation schemes (BPSK, QPSK, 8PSK, 16QAM, 64QAM) and multiple code rates within a single unified framework. The protograph serves as a universal template that can be expanded to generate codes suitable for different modulation levels and rates, eliminating the need for separate code designs for each specific modulation scheme.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the lifting factor N and the edge permutation patterns in the protograph expansion process to generate codes with different rates and performance characteristics. By changing parameters such as the lifting factor and permutation offsets, the same protograph can produce codes optimized for different modulation schemes and channel conditions.
2Adaptability or versatility
If a general protograph-based BICM framework is developed to support multiple rates and modulations, then the adaptability and efficiency are improved, but the computational complexity for calculating iterative decoding thresholds increases
Solution Approach 1:
The patent applies segmentation by dividing the threshold calculation process into separate stages: first calculating thresholds for individual protograph edge types independently using the PEXIT algorithm, then combining these results to determine the overall system threshold. This segmented approach allows for manageable computation of each edge type's contribution before aggregating the results for the complete modulation-coding system.
Solution Approach 2:
The patent introduces an intermediary framework that connects the protograph code structure with the modulation scheme through a systematic mapping relationship. This intermediary layer enables the separate analysis of code properties and modulation properties, allowing threshold calculations to be performed by bridging these two domains through defined mapping rules rather than requiring direct complex joint optimization.
3Productivity
If higher-order modulations are used to increase spectral efficiency, then the data transmission rate is improved, but the iterative decoding threshold moves further from the capacity limit
Solution Approach 1:
The patent applies local quality by optimizing the protograph structure and edge connections specifically for higher-order modulations such as 16QAM and 64QAM. Rather than using a generic code design, the protograph's variable node degrees, check node degrees, and edge permutations are locally optimized to account for the higher susceptibility to noise and interference in higher-order modulations, thereby improving the threshold performance specifically for these modulation schemes.
Solution Approach 2:
The patent employs dynamics by enabling adaptive selection of code rates and protograph expansions based on channel conditions and modulation scheme. The system can dynamically adjust the lifting factor and code rate to optimize the trade-off between spectral efficiency and decoding threshold performance for different modulation orders, allowing higher-order modulations to achieve better effective thresholds under varying operational conditions.
Data Source
AI summary
Digital communication coding methods for designing protograph-based bit-interleaved code modulation that is general and applies to any modulation. The general coding framework can support not only multiple rates but also adaptive modulation. The method is a two stage lifting approach. In the first stage, an original protograph is lifted to a slightly larger intermediate protograph. The intermediate protograph is then lifted via a circulant matrix to the expected codeword length to form a protograph-based low-density parity-check code.