20,790 research outputs found
The Degraded Gaussian Diamond-Wiretap Channel
In this paper, we present nontrivial upper and lower bounds on the secrecy
capacity of the degraded Gaussian diamond-wiretap channel and identify several
ranges of channel parameters where these bounds coincide with useful
intuitions. Furthermore, we investigate the effect of the presence of an
eavesdropper on the capacity. We consider the following two scenarios regarding
the availability of randomness: 1) a common randomness is available at the
source and the two relays and 2) a randomness is available only at the source
and there is no available randomness at the relays. We obtain the upper bound
by taking into account the correlation between the two relay signals and the
availability of randomness at each encoder. For the lower bound, we propose two
types of coding schemes: 1) a decode-and-forward scheme where the relays
cooperatively transmit the message and the fictitious message and 2) a partial
DF scheme incorporated with multicoding in which each relay sends an
independent partial message and the whole or partial fictitious message using
dependent codewords.Comment: 26 pages, 6 figures, a short version will appear in Proc. IEEE ISIT
201
A Unified Approach for Network Information Theory
In this paper, we take a unified approach for network information theory and
prove a coding theorem, which can recover most of the achievability results in
network information theory that are based on random coding. The final
single-letter expression has a very simple form, which was made possible by
many novel elements such as a unified framework that represents various network
problems in a simple and unified way, a unified coding strategy that consists
of a few basic ingredients but can emulate many known coding techniques if
needed, and new proof techniques beyond the use of standard covering and
packing lemmas. For example, in our framework, sources, channels, states and
side information are treated in a unified way and various constraints such as
cost and distortion constraints are unified as a single joint-typicality
constraint.
Our theorem can be useful in proving many new achievability results easily
and in some cases gives simpler rate expressions than those obtained using
conventional approaches. Furthermore, our unified coding can strictly
outperform existing schemes. For example, we obtain a generalized
decode-compress-amplify-and-forward bound as a simple corollary of our main
theorem and show it strictly outperforms previously known coding schemes. Using
our unified framework, we formally define and characterize three types of
network duality based on channel input-output reversal and network flow
reversal combined with packing-covering duality.Comment: 52 pages, 7 figures, submitted to IEEE Transactions on Information
theory, a shorter version will appear in Proc. IEEE ISIT 201
Noisy Network Coding with Partial DF
In this paper, we propose a noisy network coding integrated with partial
decode-and-forward relaying for single-source multicast discrete memoryless
networks (DMN's). Our coding scheme generalizes the
partial-decode-compress-and-forward scheme (Theorem 7) by Cover and El Gamal.
This is the first time the theorem is generalized for DMN's such that each
relay performs both partial decode-and-forward and compress-and-forward
simultaneously. Our coding scheme simultaneously generalizes both noisy network
coding by Lim, Kim, El Gamal, and Chung and distributed decode-and-forward by
Lim, Kim, and Kim. It is not trivial to combine the two schemes because of
inherent incompatibility in their encoding and decoding strategies. We solve
this problem by sending the same long message over multiple blocks at the
source and at the same time by letting the source find the auxiliary covering
indices that carry information about the message simultaneously over all
blocks.Comment: 5 pages, 1 figure, to appear in Proc. IEEE ISIT 201
Probing spin-charge separation using spin transport
Pedagogical discussions are given on what constitutes a signature of
spin-charge separation. A proposal is outlined to probe spin-charge separation
in the normal state of the high cuprates using spin transport.
Specifically, the proposal is to compare the temperature dependences of the
spin resistivity and electrical resistivity: Spin-charge separation will be
manifested in the different temperature dependences of these two resistivities.
We also estimate the spin diffusion length and spin relaxation time scales, and
we argue that it should be experimentally feasible to measure the spin
transport properties in the cuprates using the spin-injection technique. The
on-going spin-injection experiments in the cuprates and related theoretical
issues are also discussed.Comment: Talk given at M2S-HTSC-VI, 4 page
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