9,380 research outputs found
State Amplification Subject To Masking Constraints
This paper considers a state dependent broadcast channel with one
transmitter, Alice, and two receivers, Bob and Eve. The problem is to
effectively convey ("amplify") the channel state sequence to Bob while
"masking" it from Eve. The extent to which the state sequence cannot be masked
from Eve is referred to as leakage. This can be viewed as a secrecy problem,
where we desire that the channel state itself be minimally leaked to Eve while
being communicated to Bob. The paper is aimed at characterizing the trade-off
region between amplification and leakage rates for such a system. An achievable
coding scheme is presented, wherein the transmitter transmits a partial state
information over the channel to facilitate the amplification process. For the
case when Bob observes a stronger signal than Eve, the achievable coding scheme
is enhanced with secure refinement. Outer bounds on the trade-off region are
also derived, and used in characterizing some special case results. In
particular, the optimal amplification-leakage rate difference, called as
differential amplification capacity, is characterized for the reversely
degraded discrete memoryless channel, the degraded binary, and the degraded
Gaussian channels. In addition, for the degraded Gaussian model, the extremal
corner points of the trade-off region are characterized, and the gap between
the outer bound and achievable rate-regions is shown to be less than half a bit
for a wide set of channel parameters.Comment: Revised versio
Information Masking and Amplification: The Source Coding Setting
The complementary problems of masking and amplifying channel state
information in the Gel'fand-Pinsker channel have recently been solved by Merhav
and Shamai, and Kim et al., respectively. In this paper, we study a related
source coding problem. Specifically, we consider the two-encoder source coding
setting where one source is to be amplified, while the other source is to be
masked. In general, there is a tension between these two objectives which is
characterized by the amplification-masking tradeoff. In this paper, we give a
single-letter description of this tradeoff.
We apply this result, together with a recent theorem by Courtade and Weissman
on multiterminal source coding, to solve a fundamental entropy characterization
problem.Comment: 6 pages, 1 figure, to appear at the IEEE 2012 International Symposium
on Information Theory (ISIT 2012
State Leakage and Coordination of Actions: Core of the Receiver's Knowledge
We revisit the problems of state masking and state amplification through the
lens of empirical coordination by considering a state-dependent channel in
which the encoder has causal and strictly causal state knowledge. We show that
the problem of empirical coordination provides a natural framework in which to
jointly study the problems of reliable communication, state masking, and state
amplification. We characterize the regions of rate-equivocation-coordination
trade-offs for several channel models with causal and strictly causal state
knowledge. We introduce the notion of `core of the receiver's knowledge' to
capture what the decoder can infer about all the signals involved in the model.
We exploit this result to solve a channel state estimation zero-sum game in
which the encoder prevents the decoder to estimate the channel state
accurately.Comment: preliminary draf
Sound and noise
Sound and noise problems in space environment and human tolerance criteria at varying frequencies and intensitie
Dynamics of internetwork chromospheric fibrils: Basic properties and MHD kink waves
Using the spectroscopic imaging capabilities of the Swedish Solar Telescope,
we aim to provide the first investigation on the nature and dynamics of
elongated absorption features (fibrils) observed in H in the
internetwork. We observe and identify a number of internetwork fibrils, which
form away from the kilogauss, network magnetic flux, and we provide a synoptic
view on their behaviour. The internetwork fibrils are found to support
wave-like behaviour, which we interpret as Magnetohydrodynamic (MHD) kink
waves. The properties of these waves, that is, amplitude, period, and
propagation speed, are measured from time-distance diagrams and we attempt to
exploit them via magneto-seismology in order to probe the variation of plasma
properties along the wave-guides. We found that the Internetwork (IN) fibrils
appear, disappear, and re-appear on timescales of tens of minutes, suggesting
that they are subject to repeated heating. No clear photospheric footpoints for
the fibrils are found in photospheric magnetograms or H wing images.
However, we suggest that they are magnetised features as the majority of them
show evidence of supporting propagating MHD kink waves, with a modal period of
~s. Additionally, one IN fibril is seen to support a flow directed along
its elongated axis, suggesting a guiding field. The wave motions are found to
propagate at speeds significantly greater than estimates for typical
chromospheric sound speeds. Through their interpretation as kink waves, the
measured speeds provide an estimate for local average Alfv\'en speeds.
Furthermore, the amplitudes of the waves are also found to vary as a function
of distance along the fibrils, which can be interpreted as evidence of
stratification of the plasma in the neighbourhood of the IN fibril.Comment: Accepted Astronomy & Astrophysic
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