37 research outputs found
New Bounds for Permutation Codes in Ulam Metric
New bounds on the cardinality of permutation codes equipped with the Ulam
distance are presented. First, an integer-programming upper bound is derived,
which improves on the Singleton-type upper bound in the literature for some
lengths. Second, several probabilistic lower bounds are developed, which
improve on the known lower bounds for large minimum distances. The results of a
computer search for permutation codes are also presented.Comment: To be presented at ISIT 2015, 5 page
On Optimal Anticodes over Permutations with the Infinity Norm
Motivated by the set-antiset method for codes over permutations under the
infinity norm, we study anticodes under this metric. For half of the parameter
range we classify all the optimal anticodes, which is equivalent to finding the
maximum permanent of certain -matrices. For the rest of the cases we
show constraints on the structure of optimal anticodes
Reliability and Hardware Implementation of Rank Modulation Flash Memory
We review a novel data representation scheme for NAND flash memory named rank modulation (RM), and discuss its hardware implementation. We show that under the normal threshold voltage (Vth) variations, RM has intrinsic read reliability advantage over conventional multiple-level cells. Test results demonstrating superior reliability using commercial flash chips are reviewed and discussed. We then present a read method based on relative sensing time, which can obtain the rank of all cells in the group in one read cycle. The improvement in reliability and read speed enable similar program-and-verify time in RM as that of conventional MLC flash