24,793 research outputs found
Exploiting Spatial Interference Alignment and Opportunistic Scheduling in the Downlink of Interference Limited Systems
In this paper we analyze the performance of single stream and multi-stream
spatial multiplexing (SM) systems employing opportunistic scheduling in the
presence of interference. In the proposed downlink framework, every active user
reports the post-processing signal-to-interference-plus-noise-power-ratio
(post-SINR) or the receiver specific mutual information (MI) to its own
transmitter using a feedback channel. The combination of scheduling and
multi-antenna receiver processing leads to substantial interference suppression
gain. Specifically, we show that opportunistic scheduling exploits spatial
interference alignment (SIA) property inherent to a multi-user system for
effective interference mitigation. We obtain bounds for the outage probability
and the sum outage capacity for single stream and multi stream SM employing
real or complex encoding for a symmetric interference channel model.
The techniques considered in this paper are optimal in different operating
regimes. We show that the sum outage capacity can be maximized by reducing the
SM rate to a value less than the maximum allowed value. The optimum SM rate
depends on the number of interferers and the number of available active users.
In particular, we show that the generalized multi-user SM (MU SM) method
employing real-valued encoding provides a performance that is either
comparable, or significantly higher than that of MU SM employing complex
encoding. A combination of analysis and simulation is used to describe the
trade-off between the multiplexing rate and sum outage capacity for different
antenna configurations
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Beyond the Romance of Resistance in Post-Development Alternatives: Nature and culture in Afro-Colombian movements
Completed K-theory and Equivariant Elliptic Cohomology
Kitchloo and Morava give a strikingly simple picture of elliptic cohomology
at the Tate curve by studying a completed version of -equivariant
-theory for spaces. I present a -equivariant version of their
construction, which is a completed version of the Freed-Hopkins-Teleman model
of -theory for local quotient groupoids and resolves the issues concerning
twisting and degree that arise in a first attempt to relate their work to
elliptic cohomology.Comment: 23 page
Smoothing nilpotent actions on 1-manifolds
Let be a connected 1-manifold, i.e., , or , and let \Homeo_+(M) (resp. \Diff_+^1(M)) be the group of
orientation-preserving homeomorphisms (resp. diffeomorphisms) of . It
is a classical result that if is a finitely-generated, torsion-free
nilpotent group, then there exist 1-1 homomorphisms \phi\colon N \to
\Homeo_+(M). Farb and Franks show that, in fact, there exists a 1-1
homomorphism N \to \Diff_+^1(M). In this paper we obtain a stronger result:
every action \phi\colon N \to \Homeo_+(M) is topologically conjugate to an
action \tilde{\phi}\colon N \to \Diff_+^1(M).Comment: 16 page
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Thinking Fragments: Adisciplinary Reflections on Feminisms and Environmental Justic
Feminisms and environmental justice are some of the names of struggles to understand nature-culture linkages and conceptualize just worlds for non-humans and their human kin. In this paper, I revisit my journey of doing environmental justice research, i.e. of my feminist scientific practice in Asia and Latin America. In this retrospective telling I highlight how gender, political economy, and race were and remain fundamental in producing the subjects and objects of my research and analysis. I discuss how an implicit feminism helped me grapply with the complex nature-culture linkages I observed in the field. Postcolonial and marxist insights supplement and complement feminisms in the questions I pose as we attempt to imagine new nature-cultures
The Eternal Unprovability Filter – Part I
I prove both the mathematical conjectures P ≠ NP and the Continuum Hypothesis are eternally unprovable using the same fundamental idea. Starting with the Saunders Maclane idea that a proof is eternal or it is not a proof, I use the indeterminacy of human biological capabilities in the eternal future to show that since both conjectures are independent of Axioms and have definitions connected with human biological capabilities, it would be impossible to prove them eternally without the creation and widespread acceptance of new axioms. I also show that the same fundamental concepts cannot be used to demonstrate the eternal unprovability of many other mathematical theorems and open conjectures. Finally I investigate the idea’s implications for the foundations of mathematics including its relation to Godel’s Incompleteness Theorem and Tarsky’s Undefinability Theorem
Character Formulas from Matrix Factorisations
(With an Appendix by Constantin Teleman) In the spirit of Freed, Hopkins, and
Teleman I establish an equivalence between the category of discrete series
representations of a real semisimple Lie group G and a category of equivariant
matrix factorisations on a subset of the dual of the Lie algebra, in analogy
with the situation in [FT] which treated the case when G is compact or a loop
group thereof. The equivalence is implemented by a version of the Dirac
operator used in [FHT1-3], squaring to the superpotential W defining the matrix
factorisations. Using the structure of the resulting matrix factorisation
category as developed in [FT] I deduce the Kirillov character formula for
compact Lie groups and the Rossman character formula for the discrete series of
a real semi-simple Lie group. The proofs are a calculation of Chern characters
and use the Dirac family constructed in [FHT1-3]. Indeed, the main theorems of
[FHT3] and [FT] are a categorification of the Kirillov correspondence, and this
paper establishes that this correspondence can be recovered at the level of
characters.Comment: Appendix (by Constantin Teleman) to appear in final versio
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