6,707 research outputs found
On the Structure of the Capacity Region of Asynchronous Memoryless Multiple-Access Channels
The asynchronous capacity region of memoryless multiple-access channels is
the union of certain polytopes. It is well-known that vertices of such
polytopes may be approached via a technique called successive decoding. It is
also known that an extension of successive decoding applies to the dominant
face of such polytopes. The extension consists of forming groups of users in
such a way that users within a group are decoded jointly whereas groups are
decoded successively. This paper goes one step further. It is shown that
successive decoding extends to every face of the above mentioned polytopes. The
group composition as well as the decoding order for all rates on a face of
interest are obtained from a label assigned to that face. From the label one
can extract a number of structural properties, such as the dimension of the
corresponding face and whether or not two faces intersect. Expressions for the
the number of faces of any given dimension are also derived from the labels.Comment: 21 pages, 5 figures and 1 table. Submitted to IEEE Transactions on
Information Theor
Rigidity results and topology at infinity of translating solitons of the mean curvature flow
In this paper we obtain rigidity results and obstructions on the topology at
infinity of translating solitons of the mean curvature flow in the Euclidean
space. Our approach relies on the theory of f-minimal hypersurfaces.Comment: 18 pages. Minor corrections. Final version: to appear on Commun.
Contemp. Mat
A Tight Bound on the Performance of a Minimal-Delay Joint Source-Channel Coding Scheme
An analog source is to be transmitted across a Gaussian channel in more than
one channel use per source symbol. This paper derives a lower bound on the
asymptotic mean squared error for a strategy that consists of repeatedly
quantizing the source, transmitting the quantizer outputs in the first channel
uses, and sending the remaining quantization error uncoded in the last channel
use. The bound coincides with the performance achieved by a suboptimal decoder
studied by the authors in a previous paper, thereby establishing that the bound
is tight.Comment: 5 pages, submitted to IEEE International Symposium on Information
Theory (ISIT) 201
Asymptotically Optimal Joint Source-Channel Coding with Minimal Delay
We present and analyze a joint source-channel coding strategy for the
transmission of a Gaussian source across a Gaussian channel in n channel uses
per source symbol. Among all such strategies, our scheme has the following
properties: i) the resulting mean-squared error scales optimally with the
signal-to-noise ratio, and ii) the scheme is easy to implement and the incurred
delay is minimal, in the sense that a single source symbol is encoded at a
time.Comment: 5 pages, 1 figure, final version accepted at IEEE Globecom 2009
(Communication Theory Symposium
Stability properties and topology at infinity of f-minimal hypersurfaces
We study stability properties of -minimal hypersurfaces isometrically
immersed in weighted manifolds with non-negative Bakry-Emery Ricci curvature
under volume growth conditions. Moreover, exploiting a weighted version of a
finiteness result and the adaptation to this setting of Li-Tam theory, we
investigate the topology at infinity of -minimal hypersurfaces. On the way,
we prove a new comparison result in weighted geometry and we provide a general
weighted -Sobolev inequality for hypersurfaces in Cartan-Hadamard weighted
manifolds, satisfying suitable restrictions on the weight function.Comment: 30 pages. Final version: to appear on Geom. Dedicat
A remark on Einstein warped products
We prove triviality results for Einstein warped products with non-compact
bases. These extend previous work by D.-S. Kim and Y.-H. Kim. The proof, from
the viewpoint of "quasi-Einstein manifolds" introduced by J. Case, Y.-S. Shu
and G. Wei, rely on maximum principles at infinity and Liouville-type theorems.Comment: 12 pages. Corrected typos. Final version: to appear on Pacific J.
Mat
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