149 research outputs found
Perfectly Secure Index Coding
In this paper, we investigate the index coding problem in the presence of an
eavesdropper. Messages are to be sent from one transmitter to a number of
legitimate receivers who have side information about the messages, and share a
set of secret keys with the transmitter. We assume perfect secrecy, meaning
that the eavesdropper should not be able to retrieve any information about the
message set. We study the minimum key lengths for zero-error and perfectly
secure index coding problem. On one hand, this problem is a generalization of
the index coding problem (and thus a difficult one). On the other hand, it is a
generalization of the Shannon's cipher system. We show that a generalization of
Shannon's one-time pad strategy is optimal up to a multiplicative constant,
meaning that it obtains the entire boundary of the cone formed by looking at
the secure rate region from the origin. Finally, we consider relaxation of the
perfect secrecy and zero-error constraints to weak secrecy and asymptotically
vanishing probability of error, and provide a secure version of the result,
obtained by Langberg and Effros, on the equivalence of zero-error and
-error regions in the conventional index coding problem.Comment: 25 pages, 5 figures, submitted to the IEEE Transactions on
Information Theor
Slepian-Wolf Coding Over Cooperative Relay Networks
This paper deals with the problem of multicasting a set of discrete
memoryless correlated sources (DMCS) over a cooperative relay network.
Necessary conditions with cut-set interpretation are presented. A \emph{Joint
source-Wyner-Ziv encoding/sliding window decoding} scheme is proposed, in which
decoding at each receiver is done with respect to an ordered partition of other
nodes. For each ordered partition a set of feasibility constraints is derived.
Then, utilizing the sub-modular property of the entropy function and a novel
geometrical approach, the results of different ordered partitions are
consolidated, which lead to sufficient conditions for our problem. The proposed
scheme achieves operational separation between source coding and channel
coding. It is shown that sufficient conditions are indeed necessary conditions
in two special cooperative networks, namely, Aref network and finite-field
deterministic network. Also, in Gaussian cooperative networks, it is shown that
reliable transmission of all DMCS whose Slepian-Wolf region intersects the
cut-set bound region within a constant number of bits, is feasible. In
particular, all results of the paper are specialized to obtain an achievable
rate region for cooperative relay networks which includes relay networks and
two-way relay networks.Comment: IEEE Transactions on Information Theory, accepte
On The Positive Definiteness of Polarity Coincidence Correlation Coefficient Matrix
Polarity coincidence correlator (PCC), when used to estimate the covariance
matrix on an element-by-element basis, may not yield a positive semi-definite
(PSD) estimate. Devlin et al. [1], claimed that element-wise PCC is not
guaranteed to be PSD in dimensions p>3 for real signals. However, no
justification or proof was available on this issue. In this letter, it is
proved that for real signals with p<=3 and for complex signals with p<=2, a PSD
estimate is guaranteed. Counterexamples are presented for higher dimensions
which yield invalid covariance estimates.Comment: IEEE Signal Processing Letters, Volume 15, pp. 73-76, 200
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