64,737 research outputs found
A Unified Framework for Linear-Programming Based Communication Receivers
It is shown that a large class of communication systems which admit a
sum-product algorithm (SPA) based receiver also admit a corresponding
linear-programming (LP) based receiver. The two receivers have a relationship
defined by the local structure of the underlying graphical model, and are
inhibited by the same phenomenon, which we call 'pseudoconfigurations'. This
concept is a generalization of the concept of 'pseudocodewords' for linear
codes. It is proved that the LP receiver has the 'maximum likelihood
certificate' property, and that the receiver output is the lowest cost
pseudoconfiguration. Equivalence of graph-cover pseudoconfigurations and
linear-programming pseudoconfigurations is also proved. A concept of 'system
pseudodistance' is defined which generalizes the existing concept of
pseudodistance for binary and nonbinary linear codes. It is demonstrated how
the LP design technique may be applied to the problem of joint equalization and
decoding of coded transmissions over a frequency selective channel, and a
simulation-based analysis of the error events of the resulting LP receiver is
also provided. For this particular application, the proposed LP receiver is
shown to be competitive with other receivers, and to be capable of
outperforming turbo equalization in bit and frame error rate performance.Comment: 13 pages, 6 figures. To appear in the IEEE Transactions on
Communication
Codeword-Independent Performance of Nonbinary Linear Codes Under Linear-Programming and Sum-Product Decoding
A coded modulation system is considered in which nonbinary coded symbols are
mapped directly to nonbinary modulation signals. It is proved that if the
modulator-channel combination satisfies a particular symmetry condition, the
codeword error rate performance is independent of the transmitted codeword. It
is shown that this result holds for both linear-programming decoders and
sum-product decoders. In particular, this provides a natural modulation mapping
for nonbinary codes mapped to PSK constellations for transmission over
memoryless channels such as AWGN channels or flat fading channels with AWGN.Comment: 5 pages, Proceedings of the 2008 IEEE International Symposium on
Information Theory, Toronto, ON, Canada, July 6-11, 200
Weak hyperbolicity of cube complexes and quasi-arboreal groups
We examine a graph encoding the intersection of hyperplane carriers
in a CAT(0) cube complex . The main result is that is
quasi-isometric to a tree. This implies that a group acting properly and
cocompactly on is weakly hyperbolic relative to the hyperplane
stabilizers. Using disc diagram techniques and Wright's recent result on the
aymptotic dimension of CAT(0) cube complexes, we give a generalization of a
theorem of Bell and Dranishnikov on the finite asymptotic dimension of graphs
of asymptotically finite-dimensional groups. More precisely, we prove
asymptotic finite-dimensionality for finitely-generated groups acting on
finite-dimensional cube complexes with 0-cube stabilizers of uniformly bounded
asymptotic dimension. Finally, we apply contact graph techniques to prove a
cubical version of the flat plane theorem stated in terms of complete bipartite
subgraphs of .Comment: Corrections in Sections 2 and 4. Simplification in Section
Review of \u3ci\u3eThe Army and Democracy: Military Politics in Pakistan\u3c/i\u3e by Aqil Shah
Cocompactly cubulated crystallographic groups
We prove that the simplicial boundary of a CAT(0) cube complex admitting a
proper, cocompact action by a virtually \integers^n group is isomorphic to
the hyperoctahedral triangulation of , providing a class of groups
for which the simplicial boundary of a -cocompact cube complex depends only
on . We also use this result to show that the cocompactly cubulated
crystallographic groups in dimension are precisely those that are
\emph{hyperoctahedral}. We apply this result to answer a question of Wise on
cocompactly cubulating virtually free abelian groups.Comment: Several correction
Bibliographic Guide to the Terrestrial Arthropods of Michigan
Papers dealing with distribution, faunal extensions, and identification of Michigan insects and other terrestrial arthropods are listed by order, and cover the period of 1878 through 1982
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