Adaptive LDPC Parity-Check Matrices for Variable-Iteration Decoding

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Solution Overview

Problem

Conventional adaptive modulation and coding (AMC) systems fail to optimize low-density parity-check (LDPC) codes for various high-order and high-dimensional modulation formats, leading to suboptimal performance and increased complexity in error control for digital data communications.

Innovation Solution

The proposed solution involves adapting the parity-check matrix (PCM) for finite-iteration decoders and any modulation format, allowing for the selection of the best LDPC code and modulation based on channel quality and receiver behavior, while minimizing computational complexity and power consumption. This is achieved by pre-designing PCMs for different modulation formats, iteration numbers, and decoding algorithms, and using spatially coupled and nonbinary LDPC codes to optimize degree distributions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional AMC uses multiple LDPC codes with different code rates, then data rate adaptation is achieved, but performance optimization for various high-order and high-dimensional modulation formats cannot be achieved

Engineering Contradiction:

Improvemodulation format adaptabilityVSAvoidBER performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the degree distribution parameter of LDPC codes to optimize performance for different modulation formats. By adjusting the degree distribution rather than using completely different codes, the system achieves format-specific optimization while maintaining code rate flexibility. This allows the same base LDPC code structure to be adapted for various modulation schemes including high-order and high-dimensional formats.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent segments the LDPC code design into modular components: base degree distribution, modulation-specific degree distribution adjustments, and format-adaptive selection. This segmentation allows independent optimization for each modulation format while maintaining overall system coherence and enabling efficient switching between formats without redesigning entire codes.

Inventive Principle:

Principle #1Segmentation

2Reliability

If BICM-ID is used for high-order modulation formats, then performance approaches MLC bound, but latency increases due to soft-decision feedback requirement

Engineering Contradiction:

ImproveBER performanceVSAvoiddecoding latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies partial feedback by using only the necessary extrinsic information from the decoder for degree distribution adaptation, rather than full soft-decision feedback required by BICM-ID. This partial action achieves performance close to MLC by optimizing the degree distribution based on channel conditions and modulation format, while avoiding the excessive latency of complete iterative demodulation- decoding feedback loops.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If MLC is used for high-order modulation formats, then best theoretical performance is achieved, but codeword length shortening occurs for each layered code

Engineering Contradiction:

ImproveBER performanceVSAvoidcodeword length

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The patent creates a universal LDPC code design that serves multiple modulation formats through degree distribution adaptation rather than requiring separate layered codes for each format. This multi-functional approach allows a single code structure to be optimized for different modulation schemes, avoiding the codeword length shortening that occurs when multiple specialized codes are used in MLC.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Manufacturing precision

If EXIT or DE methods are used for LDPC code design, then good degree distribution can be designed, but practical limitations in memory size, bit width precision, and maximum iterations are not accounted for

Engineering Contradiction:

Improvedegree distribution optimizationVSAvoidimplementation complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent modifies the degree distribution parameters based on practical implementation constraints including memory size, bit width precision, and maximum iteration limits. By adjusting these parameters within the degree distribution framework rather than using idealized infinite-precision designs, the system achieves optimal performance that is actually implementable in real-world systems with finite resources.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9722633B2Method and system for reliable data communications with adaptive multi-dimensional modulations for variable-iteration decoding

Publication Date: 2017.08.01 MITSUBISHI ELECTRIC RESEARCH LABORATORIES INC

AI summary

In an advanced adaptive modulation and coding (AMC) scheme, the code rate and the parity-check matrix (PCM) for low-density parity-check (LDPC) codes are adapted according to modulation formats and variable-iteration receivers. The degree distribution for the PCM adaptation is designed by heuristic optimization to minimize the required SNR via an extrinsic information transfer (EXIT) trajectory analysis for finite-iteration decoding. The method uses dynamic window decoding by generating spatially coupled PCM for quasi-cyclic LDPC convolutional coding. The method also provides a way to jointly optimize labeling and decoding complexity for high-order and high-dimensional modulations.