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Enhanced Precision Through Multiple Reads for LDPC Decoding in Flash Memories

delete2014-05-01
delete97
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OA
AI
J
Jiadong Wang *
K
Kasra Vakilinia
T
Tsung‐Yi Chen
T
Thomas A. Courtade
G
Guiqiang Dong
T
Tong Zhang
H
Hari Shankar
R
Richard D. Wesel
DOI:10.1109/JSAC.2014.140508delete
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Abstract

Abstract

En 中文
Multiple reads of the same Flash memory cell with distinct word-line voltages provide enhanced precision for LDPC decoding. In this paper, the word-line voltages are optimized by maximizing the mutual information (MI) of the quantized channel. The enhanced precision from a few additional reads allows frame error rate (FER) performance to approach that of full-precision soft information and enables an LDPC code to significantly outperform a BCH code. A constant-ratio constraint provides a significant simplification in the optimization with no noticeable loss in performance. For a well-designed LDPC code, the quantization that maximizes the mutual information also minimizes the FER in our simulations. However, for an example LDPC code with a high error floor caused by small absorbing sets, the MMI quantization does not provide the lowest frame error rate. The best quantization in this case introduces more erasures than would be optimal for the channel MI in order to mitigate the absorbing sets of the poorly designed code. The paper also identifies a trade-off in LDPC code design when decoding is performed with multiple precision levels; the best code at one level of precision will typically not be the best code at a different level of precision.
Keywords:
Flash Memory
LDPC Codes
Quantization
Mutual Information Maximization
LDPC Decoding
Soft Information
Enhanced Precision

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IEEE Journal on Selected Areas in Communications cover
IEEE Journal on Selected Areas in Communications
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