研究概要 |
Several new coding methods to increase the reliability of flash memory systems were obtained; five major results are described here. (1) Multi-level flash memory can be viewed as a coded-modulated system, and lattices were combined with Reed-Solomon error-correcting codes. This gave a significant gain over current flash memory systems, and was published in IEEE Journal on Selected Areas in Communications (IEEE JSAC). (2) Write once memory (WOM) codes are a coding theoretic method to increase the longevity of flash memories. New lattice-based WOM codes for multilevel flash memories were described. The new codes approach the theoretical capacity, when the number of levels goes to infinity; this was published in a separate IEEE JSAC article. (3) There is a tight connection between WOM codes and the interference channel (particularly dirty paper coding). A scheme which takes advantage of dirty paper coding to design multi-level WOM codes was given, and was presented at IEEE ICC in Budapest, Hungary. (4) New binary WOM codes which also correct errors was given. This new construction has a higher coding rate than the existing method, and was presented at IEEE International Symposium on Information Theory in Istanbul, Turkey. (5) A powerful technique to optimally quantize channels will be published in IEEE Transactions on Information Theory (later in 2014). Also, in May 2013, the "Workshop on Coding for Flash Memories" was held in Fukui-ken, Awara-shi, which gathered Japanese and international researchers to fruitfully discuss research and disseminate ideas.
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