Nonbinary WOM Codes With Uninformed Encoder and Decoder

Abstract

Write-once memory (WOM) is a storage device, where the cells can only be increased when programmed. A WOM code allows the device to be programmed multiple times without decreasing the cell values. This will allow a longer lifetime in, e.g., flash memory, where frequent erasures wear it out. Most WOM codes assume that the previous state is available when encoding a message; however, this is impractical as it requires an additional read operation before encoding can be performed. In this letter, we will consider the case where neither the encoder nor the decoder knows the previous state of the memory. Furthermore, we will present a WOM code for nonbinary cells, i.e., where each cell can store q different values. We will derive the sum rate of this code and show that it exceeds that of the previous designs.