3,331 research outputs found
Finite-key security analysis of quantum key distribution with imperfect light sources
In recent years, the gap between theory and practice in quantum key
distribution (QKD) has been significantly narrowed, particularly for QKD
systems with arbitrarily awed optical receivers. The status for QKD systems
with imperfect light sources is however less satisfactory, in the sense that
the resulting secure key rates are often overly-dependent on the quality of
state preparation. This is especially the case when the channel loss is high.
Very recently, to overcome this limitation, Tamaki et al proposed a QKD
protocol based on the so-called rejected data analysis, and showed that its
security|in the limit of infinitely long keys|is almost independent of any
encoding flaw in the qubit space, being this protocol compatible with the decoy
state method. Here, as a step towards practical QKD, we show that a similar
conclusion is reached in the finite-key regime, even when the intensity of the
light source is unstable. More concretely, we derive security bounds for a wide
class of realistic light sources and show that the bounds are also efficient in
the presence of high channel loss. Our results strongly suggest the feasibility
of long distance provably-secure communication with imperfect light sources.Comment: 27 pages, 7 figure
The Three-Terminal Interactive Lossy Source Coding Problem
The three-node multiterminal lossy source coding problem is investigated. We
derive an inner bound to the general rate-distortion region of this problem
which is a natural extension of the seminal work by Kaspi'85 on the interactive
two-terminal source coding problem. It is shown that this (rather involved)
inner bound contains several rate-distortion regions of some relevant source
coding settings. In this way, besides the non-trivial extension of the
interactive two terminal problem, our results can be seen as a generalization
and hence unification of several previous works in the field. Specializing to
particular cases we obtain novel rate-distortion regions for several lossy
source coding problems. We finish by describing some of the open problems and
challenges. However, the general three-node multiterminal lossy source coding
problem seems to offer a formidable mathematical complexity.Comment: New version with changes suggested by reviewers.Revised and
resubmitted to IEEE Transactions on Information Theory. 92 pages, 11 figures,
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Electronics systems test laboratory testing of shuttle communications systems
Shuttle communications and tracking systems space to space and space to ground compatibility and performance evaluations are conducted in the NASA Johnson Space Center Electronics Systems Test Laboratory (ESTL). This evaluation is accomplished through systems verification/certification tests using orbiter communications hardware in conjunction with other shuttle communications and tracking external elements to evaluate end to end system compatibility and to verify/certify that overall system performance meets program requirements before manned flight usage. In this role, the ESTL serves as a multielement major ground test facility. The ESTL capability and program concept are discussed. The system test philosophy for the complex communications channels is described in terms of the major phases. Results of space to space and space to ground systems tests are presented. Several examples of the ESTL's unique capabilities to locate and help resolve potential problems are discussed in detail
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