796 research outputs found
Rewriting Flash Memories by Message Passing
This paper constructs WOM codes that combine rewriting and error correction
for mitigating the reliability and the endurance problems in flash memory. We
consider a rewriting model that is of practical interest to flash applications
where only the second write uses WOM codes. Our WOM code construction is based
on binary erasure quantization with LDGM codes, where the rewriting uses
message passing and has potential to share the efficient hardware
implementations with LDPC codes in practice. We show that the coding scheme
achieves the capacity of the rewriting model. Extensive simulations show that
the rewriting performance of our scheme compares favorably with that of polar
WOM code in the rate region where high rewriting success probability is
desired. We further augment our coding schemes with error correction
capability. By drawing a connection to the conjugate code pairs studied in the
context of quantum error correction, we develop a general framework for
constructing error-correction WOM codes. Under this framework, we give an
explicit construction of WOM codes whose codewords are contained in BCH codes.Comment: Submitted to ISIT 201
Quantum-Assisted Telescope Arrays
Quantum networks provide a platform for astronomical interferometers capable
of imaging faint stellar objects. In a recent work [arXiv:1809.01659], we
presented a protocol that circumvents transmission losses with efficient use of
quantum resources and modest quantum memories. Here we analyze a number of
extensions to that scheme. We show that it can be operated as a truly broadband
interferometer and generalized to multiple sites in the array. We also analyze
how imaging based on the quantum Fourier transform provides improved
signal-to-noise ratio compared to classical processing. Finally, we discuss
physical realizations including photon-detection-based quantum state transfer.Comment: 10 pages, 8 figures; v2 - clarifications and references; v3 - close
to published versio
Flash-memories in Space Applications: Trends and Challenges
Nowadays space applications are provided with a processing power absolutely overcoming the one available just a few years ago. Typical mission-critical space system applications include also the issue of solid-state recorder(s). Flash-memories are nonvolatile, shock-resistant and power-economic, but in turn have different drawbacks. A solid-state recorder for space applications should satisfy many different constraints especially because of the issues related to radiations: proper countermeasures are needed, together with EDAC and testing techniques in order to improve the dependability of the whole system. Different and quite often contrasting dimensions need to be explored during the design of a flash-memory based solid- state recorder. In particular, we shall explore the most important flash-memory design dimensions and trade-offs to tackle during the design of flash-based hard disks for space application
LDPC Codes with Local and Global Decoding
This paper presents a theoretical study of a new type of LDPC codes motivated
by practical storage applications. LDPCL codes (suffix L represents locality)
are LDPC codes that can be decoded either as usual over the full code block, or
locally when a smaller sub-block is accessed (to reduce latency). LDPCL codes
are designed to maximize the error-correction performance vs. rate in the usual
(global) mode, while at the same time providing a certain performance in the
local mode. We develop a theoretical framework for the design of LDPCL codes.
Our results include a design tool to construct an LDPC code with two
data-protection levels: local and global. We derive theoretical results
supporting this tool and we show how to achieve capacity with it. A trade-off
between the gap to capacity and the number of full-block accesses is studied,
and a finite-length analysis of ML decoding is performed to exemplify a
trade-off between the locality capability and the full-block error-correcting
capability.Comment: 41 page
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