On rate tradeoffs for erasable write-once memory codes

To formulate rewriting operations on flash memory, we extend Write-Once Memory (WOM) and introduce Erasable WOM (EWOM) which allows block erasures, and then we define codes to rewrite on them. To measure performances of EWOM codes, we introduce the rate tradeoff pair, which is derived from the sum rate. We give an outer bound of the region of the possible tradeoff pairs for a certain class of EWOM´s. We also propose fixed-rate EWOM codes calledWOM2E codes that utilize existing WOM codes. It reveals that WOM2E scheme is optimal in terms of rate tradeoff pair when the block size of EWOM is “infinity.”