13,373 research outputs found
Are Slepian-Wolf Rates Necessary for Distributed Parameter Estimation?
We consider a distributed parameter estimation problem, in which multiple
terminals send messages related to their local observations using limited rates
to a fusion center who will obtain an estimate of a parameter related to
observations of all terminals. It is well known that if the transmission rates
are in the Slepian-Wolf region, the fusion center can fully recover all
observations and hence can construct an estimator having the same performance
as that of the centralized case. One natural question is whether Slepian-Wolf
rates are necessary to achieve the same estimation performance as that of the
centralized case. In this paper, we show that the answer to this question is
negative. We establish our result by explicitly constructing an asymptotically
minimum variance unbiased estimator (MVUE) that has the same performance as
that of the optimal estimator in the centralized case while requiring
information rates less than the conditions required in the Slepian-Wolf rate
region.Comment: Accepted in Allerton 201
The Relay-Eavesdropper Channel: Cooperation for Secrecy
This paper establishes the utility of user cooperation in facilitating secure
wireless communications. In particular, the four-terminal relay-eavesdropper
channel is introduced and an outer-bound on the optimal rate-equivocation
region is derived. Several cooperation strategies are then devised and the
corresponding achievable rate-equivocation region are characterized. Of
particular interest is the novel Noise-Forwarding (NF) strategy, where the
relay node sends codewords independent of the source message to confuse the
eavesdropper. This strategy is used to illustrate the deaf helper phenomenon,
where the relay is able to facilitate secure communications while being totally
ignorant of the transmitted messages. Furthermore, NF is shown to increase the
secrecy capacity in the reversely degraded scenario, where the relay node fails
to offer performance gains in the classical setting. The gain offered by the
proposed cooperation strategies is then proved theoretically and validated
numerically in the additive White Gaussian Noise (AWGN) channel.Comment: 33 pages, submitted to IEEE Transactions on Information Theor
The Three Node Wireless Network: Achievable Rates and Cooperation Strategies
We consider a wireless network composed of three nodes and limited by the
half-duplex and total power constraints. This formulation encompasses many of
the special cases studied in the literature and allows for capturing the common
features shared by them. Here, we focus on three special cases, namely 1) Relay
Channel, 2) Multicast Channel, and 3) Conference Channel. These special cases
are judicially chosen to reflect varying degrees of complexity while
highlighting the common ground shared by the different variants of the three
node wireless network. For the relay channel, we propose a new cooperation
scheme that exploits the wireless feedback gain. This scheme combines the
benefits of decode-and-forward and compress-and-forward strategies and avoids
the idealistic feedback assumption adopted in earlier works. Our analysis of
the achievable rate of this scheme reveals the diminishing feedback gain at
both the low and high signal-to-noise ratio regimes. Inspired by the proposed
feedback strategy, we identify a greedy cooperation framework applicable to
both the multicast and conference channels. Our performance analysis reveals
several nice properties of the proposed greedy approach and the central role of
cooperative source-channel coding in exploiting the receiver side information
in the wireless network setting. Our proofs for the cooperative multicast with
side-information rely on novel nested and independent binning encoders along
with a list decoder.Comment: 52 page
On the Secrecy Capacity of Fading Channels
We consider the secure transmission of information over an ergodic fading
channel in the presence of an eavesdropper. Our eavesdropper can be viewed as
the wireless counterpart of Wyner's wiretapper. The secrecy capacity of such a
system is characterized under the assumption of asymptotically long coherence
intervals. We first consider the full Channel State Information (CSI) case,
where the transmitter has access to the channel gains of the legitimate
receiver and the eavesdropper. The secrecy capacity under this full CSI
assumption serves as an upper bound for the secrecy capacity when only the CSI
of the legitimate receiver is known at the transmitter, which is characterized
next. In each scenario, the perfect secrecy capacity is obtained along with the
optimal power and rate allocation strategies. We then propose a low-complexity
on/off power allocation strategy that achieves near-optimal performance with
only the main channel CSI. More specifically, this scheme is shown to be
asymptotically optimal as the average SNR goes to infinity, and interestingly,
is shown to attain the secrecy capacity under the full CSI assumption.
Remarkably, our results reveal the positive impact of fading on the secrecy
capacity and establish the critical role of rate adaptation, based on the main
channel CSI, in facilitating secure communications over slow fading channels.Comment: 18 pages, 3 figures, Submitted to the IEEE Trans. on Information
Theor
The Wiretap Channel with Feedback: Encryption over the Channel
In this work, the critical role of noisy feedback in enhancing the secrecy
capacity of the wiretap channel is established. Unlike previous works, where a
noiseless public discussion channel is used for feedback, the feed-forward and
feedback signals share the same noisy channel in the present model. Quite
interestingly, this noisy feedback model is shown to be more advantageous in
the current setting. More specifically, the discrete memoryless modulo-additive
channel with a full-duplex destination node is considered first, and it is
shown that the judicious use of feedback increases the perfect secrecy capacity
to the capacity of the source-destination channel in the absence of the
wiretapper. In the achievability scheme, the feedback signal corresponds to a
private key, known only to the destination. In the half-duplex scheme, a novel
feedback technique that always achieves a positive perfect secrecy rate (even
when the source-wiretapper channel is less noisy than the source-destination
channel) is proposed. These results hinge on the modulo-additive property of
the channel, which is exploited by the destination to perform encryption over
the channel without revealing its key to the source. Finally, this scheme is
extended to the continuous real valued modulo- channel where it is
shown that the perfect secrecy capacity with feedback is also equal to the
capacity in the absence of the wiretapper.Comment: Submitted to IEEE Transactions on Information Theor
Cognitive Medium Access: Exploration, Exploitation and Competition
This paper establishes the equivalence between cognitive medium access and
the competitive multi-armed bandit problem. First, the scenario in which a
single cognitive user wishes to opportunistically exploit the availability of
empty frequency bands in the spectrum with multiple bands is considered. In
this scenario, the availability probability of each channel is unknown to the
cognitive user a priori. Hence efficient medium access strategies must strike a
balance between exploring the availability of other free channels and
exploiting the opportunities identified thus far. By adopting a Bayesian
approach for this classical bandit problem, the optimal medium access strategy
is derived and its underlying recursive structure is illustrated via examples.
To avoid the prohibitive computational complexity of the optimal strategy, a
low complexity asymptotically optimal strategy is developed. The proposed
strategy does not require any prior statistical knowledge about the traffic
pattern on the different channels. Next, the multi-cognitive user scenario is
considered and low complexity medium access protocols, which strike the optimal
balance between exploration and exploitation in such competitive environments,
are developed. Finally, this formalism is extended to the case in which each
cognitive user is capable of sensing and using multiple channels
simultaneously.Comment: Submitted to IEEE/ACM Trans. on Networking, 14 pages, 2 figure
Distinctive patterns of macrolide-lincosamide-streptogramin resistance phenotypes and determinants amongst Staphylococcus aureus populations in Hong Kong
postprin
miRNAs as Regulators of Antidiabetic Effects of Fucoidans
open access articleDiabetes mellitus is a metabolic disease with a high mortality rate worldwide. MicroRNAs (miRNAs), and other small noncoding RNAs, serve as endogenous gene regulators through binding to specific sequences in RNA and modifying gene expression toward up- or down-regulation. miRNAs have become compelling therapeutic targets and play crucial roles in regulating the process of insulin resistance. Fucoidan has shown potential function as an a-amylase inhibitor, which may be beneficial in the management of type 2 diabetes mellitus. In recent years, many studies on fucoidan focused on the decrease in blood glucose levels caused by ingesting low-glucose food or glucose-lowering components. However, the importance of miRNAs as regulators of antidiabetic effects was rarely recognized. Hence, this review emphasizes the antidiabetic mechanisms of fucoidan through regulation of miRNAs. Fucoidan exerts a vital antidiabetic effect by regulation of miRNA expression and thus provides a novel biological target for future research
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