Flash Memory GLDPC Decoding With Adaptive Bit-Flip Thresholds
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Solution Overview
Problem
Current decoding algorithms for Generalized Low-Density Parity-Check (GLDPC) codes in NAND-type flash memory systems are complex and not optimized for low error correction, as they apply a fixed threshold for all bits, which is inefficient for varying error conditions.
Innovation Solution
A bit-flipping (BF) decoder with adaptive thresholding is used, where the reliability indicator for each bit is computed based on its degree and unsatisfied check (USC) information, allowing the threshold to vary and improving error correction capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed threshold is used for all bits in GLDPC decoding, then the decoding algorithm is simpler, but the error correction capability is reduced
Solution Approach 1:
The patent applies local quality by using different threshold values for different bits based on their degree (number of connections in the parity check matrix). Instead of a uniform threshold, each bit position receives a tailored threshold that reflects its local characteristics in the code structure, thereby improving error correction capability without significantly increasing overall complexity
Solution Approach 2:
The patent implements dynamics by making the threshold adaptive rather than fixed. The threshold for each bit is dynamically adjusted based on the degree of that bit and the iteration number, allowing the decoding process to adapt to the specific error patterns and convergence characteristics observed during decoding
2Reliability
If complex decoding algorithms are used for GLDPC codes, then error correction capability is improved, but the device complexity increases
Solution Approach 1:
The patent changes key parameters of the bit-flipping decoder, specifically the threshold parameter and the bit selection criterion. By modifying these parameters to be degree-dependent and adaptive, the patent achieves improved error correction performance while maintaining the relatively simple bit-flipping framework, avoiding the need for much more complex algorithms
3Reliability
If adaptive thresholding based on bit degree and USC information is implemented, then error correction capability is enhanced, but the computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the degree of each bit position before decoding begins. This pre-computed information is then readily available during decoding to guide threshold selection and bit flipping decisions, avoiding the need for complex real-time calculations during the actual decoding process
Data Source
AI summary
Memory controllers, decoders and methods perform decoding of a codeword comprising multiple bits. For a select one of those bits, which belongs to at least one component codeword of the codeword, at an iteration of decoding, the following operations are performed. Channel information for the select bit is biased based on degree of the select bit. A reliability indicator of an initial decision as to whether to flip the select bit is computed based on the initial decision and the biased channel information. The reliability indicator is compared with an adaptive threshold, which is determined based on the degree of the select bit and unsatisfied check (USC) information from the initial decision. A decision is then made as to whether to flip the select bit. The decision and syndromes of each component codeword to which the select bit belongs are updated based on the compare operation.