Irregular LDPC Decoding with Weighted Checksums and Node Scaling

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Solution Overview

Problem

Irregular low-density parity-check (LDPC) codes face challenges in error correction due to irregular column and row weights, leading to a weak correlation between checksum and remaining errors, which affects decoding performance and increases the error floor, especially in NAND flash memory systems.

Innovation Solution

The method involves constraining the parity check matrix into regions with different weights, estimating errors using weighted checksums based on high and low degree nodes, and applying scaling factors to LDPC decoders to improve decoding performance and reduce the error floor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If irregular LDPC codes are used to improve decoding performance and reduce error floor, then reliability is improved, but device complexity increases due to varying column and row weights in the parity-check matrix

Engineering Contradiction:

Improvedecoding performanceVSAvoidparity-check matrix structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The parity-check matrix is segmented into different regions based on column weight characteristics. High-degree columns (with weight ≥ threshold) are separated from low-degree columns, allowing different processing strategies for different segments. This segmentation enables the system to handle the complexity of irregular LDPC codes by dividing them into manageable regions with distinct properties.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different scaling factors are applied to different regions of the parity-check matrix based on their local characteristics. High-degree column regions receive one scaling factor while low-degree column regions receive another scaling factor. This local quality approach allows the system to optimize decoding performance for each region according to its specific weight characteristics, thereby improving overall reliability while managing device complexity through targeted rather than uniform processing.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If scaling factors are applied to high and low degree nodes separately to improve error estimation accuracy, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improveerror estimation accuracyVSAvoiddecoder structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system changes the parameter of scaling factors applied to different node types in the LDPC decoder. By identifying high-degree nodes and low-degree nodes separately and applying different scaling factors to each group, the system improves error estimation accuracy. This parameter change approach allows the decoder to adapt its processing characteristics based on node degree, enhancing measurement precision without requiring a complete redesign of the decoder architecture.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11881871B1On-the-fly scaling factor change for irregular LDPC codes

Publication Date: 2024.01.23 SK HYNIX INC

AI summary

Decoding method and memory system that decodes data and estimates a weighted checksum on the decoded data to determine whether the decoding is successful. The weighted checksum is calculated based on a first group and a second group, the first group is associated with weights for high degree nodes of an irregular parity check matrix, and the second group is associated with weights for low degree nodes of the irregular parity check matrix.