相变存储器的时空约束编码
Time-Space Constrained Codes for Phase-Change Memories
摘要：
相变存储器（PCM）是一种很有前途的非易失性固态存储技术。PCM单元通过使用其非晶态和晶态来存储数据。电池利用高温在这两种状态之间变化。然而，由于单元对高温敏感，因此在对单元编程时，重要的是在时间和空间上平衡热量。本文研究了PCM码的时空约束问题，该问题最初是由Jiang等人提出的.如果对于任何$α$连续重写和对于$β$连续信元的任何段，$β$信元在这些$α$重写上的总重写开销至多为$p$，则称之为\emph{$(α,β,p)$-constrained code}.这里，单元是二进制的，重写成本被定义为当前和下一个存储器状态之间的汉明距离。首先，我们给出了这些码的可达速率的一般上界，推广了Jiang等人的结果，然后，我们将其构造推广到$(α\geq 1, β=1,p=1)$约束码，并给出了$(α= 1, β\geq 1,p\geq1)$约束码的另一种构造.最后，我们表明，这两个结构可以用来构造代码的所有值的$α$，$β$，和$p$。
英文摘要：
Phase-change memory (PCM) is a promising non-volatile solid-state memory technology. A PCM cell stores data by using its amorphous and crystalline states. The cell changes between these two states using high temperature. However, since the cells are sensitive to high temperature, it is important, when programming cells, to balance the heat both in time and space. In this paper, we study the time-space constraint for PCM, which was originally proposed by Jiang et al. A code is called an \emph{$(α,β,p)$-constrained code} if for any $α$ consecutive rewrites and for any segment of $β$ contiguous cells, the total rewrite cost of the $β$ cells over those $α$ rewrites is at most $p$. Here, the cells are binary and the rewrite cost is defined to be the Hamming distance between the current and next memory states. First, we show a general upper bound on the achievable rate of these codes which extends the results of Jiang et al. Then, we generalize their construction for $(α\geq 1, β=1,p=1)$-constrained codes and show another construction for $(α= 1, β\geq 1,p\geq1)$-constrained codes. Finally, we show that these two constructions can be used to construct codes for all values of $α$, $β$, and $p$.
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