Layered LDPC Message Precision for Error Floor Reliability
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Solution Overview
Problem
Existing LDPC code decoders face issues with high error floors due to insufficient message precision, leading to near-codeword failures and catastrophic errors, especially in the error floor region of the performance curve, which affects data transmission reliability and rate.
Innovation Solution
Optimizing the precision of a-posteriori P type messages and Q type messages in the message passing algorithm, and selecting appropriate precisions for messages passed between the SISO channel detector and the LDPC decoder to avoid catastrophic errors and reduce near-codeword failures, by freezing messages when they reach saturation or setting precisions based on channel type and performance requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If finite precision is used for message passing in layered LDPC decoders, then computational complexity is reduced and implementation becomes feasible, but error floor performance deteriorates due to near-codeword failures and catastrophic errors
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the precision of message passing based on the decoding state. Specifically, the precision of P type messages (a-posteriori probabilities) and Q type messages (messages from variable nodes to check nodes) is optimized to different values depending on the iteration stage and error conditions, thereby resolving the contradiction between finite precision implementation and error floor performance
Solution Approach 2:
The patent implements dynamic precision adjustment where the message precision is not fixed but changes during the decoding process. The system transitions from lower precision in early iterations to higher precision when near-codeword failures are detected, making the decoder adaptive to the current decoding state and preventing catastrophic errors while maintaining computational feasibility
2Reliability
If message precision is increased to avoid catastrophic errors, then reliability improves, but computational complexity and resource requirements increase
Solution Approach 1:
The patent applies local quality by assigning different precision levels to different message types (P type and Q type messages) rather than using uniform high precision throughout. This allows the system to maintain high reliability where needed (in messages critical for avoiding catastrophic errors) while using lower precision elsewhere, thus improving reliability without proportionally increasing overall computational complexity
Data Source
AI summary
Systems and methods are provided for selecting precisions during iterative decoding with a low-density parity check (LDPC) decoder in order to maximize LDPC code's performance in the error floor region. The selection of the precision of the messages may be done in such a way as to avoid catastrophic errors and to minimize the number of near-codeword errors during the decoding process. Another system and method to avoid catastrophic errors in the layered (serial) LDPC decoder is provided. Lastly, a system and method that select precisions and provide circuitry that optimizes the exchange of information between a soft-input, soft-output (SISO) channel detector and an error correction code (ECC) decoder for channels with memory is provided.