论文标题
Nand Flash的自适应读取阈值
Adaptive Read Thresholds for NAND Flash
论文作者
论文摘要
NAND闪光灯上阅读时间增加的主要来源来自这样一个事实，即在存在噪声的情况下，必须使用不同的读取阈值电压来读取闪光灯介质才能成功。本文提出了一种算法，该算法使用有限数量的重读来表征噪声分布并恢复存储的信息。都考虑了硬解码和软解码。对于硬解码，该纸张试图找到一个读取阈值最小化位率率（BER），并为由此产生的代码字rate速率得出一个表达式。对于软解码，它表明，在有限的允许重新阅读的情况下，将BER和最小化代码字率最小化是竞争目标，并提议在两者之间进行权衡。 提出的方法不需要关于噪声分布的任何先验知识，但是可以在此类信息时利用。每个读取阈值都是根据先前读取的结果选择的，这是通过动态编程向后递归得出的最佳策略。从SLC闪存的角度研究了该方法和结果，每个级别都具有高斯噪声，但论文解释了该方法如何扩展到其他情况。
A primary source of increased read time on NAND flash comes from the fact that in the presence of noise, the flash medium must be read several times using different read threshold voltages for the decoder to succeed. This paper proposes an algorithm that uses a limited number of re-reads to characterize the noise distribution and recover the stored information. Both hard and soft decoding are considered. For hard decoding, the paper attempts to find a read threshold minimizing bit-error-rate (BER) and derives an expression for the resulting codeword-error-rate. For soft decoding, it shows that minimizing BER and minimizing codeword-error-rate are competing objectives in the presence of a limited number of allowed re-reads, and proposes a trade-off between the two. The proposed method does not require any prior knowledge about the noise distribution, but can take advantage of such information when it is available. Each read threshold is chosen based on the results of previous reads, following an optimal policy derived through a dynamic programming backward recursion. The method and results are studied from the perspective of an SLC Flash memory with Gaussian noise for each level but the paper explains how the method could be extended to other scenarios.
