10,793 research outputs found
Advanced Coordinated Beamforming for the Downlink of Future LTE Cellular Networks
Modern cellular networks in traditional frequency bands are notoriously
interference-limited especially in urban areas, where base stations are
deployed in close proximity to one another. The latest releases of Long Term
Evolution (LTE) incorporate features for coordinating downlink transmissions as
an efficient means of managing interference. Recent field trial results and
theoretical studies of the performance of joint transmission (JT) coordinated
multi-point (CoMP) schemes revealed, however, that their gains are not as high
as initially expected, despite the large coordination overhead. These schemes
are known to be very sensitive to defects in synchronization or information
exchange between coordinating bases stations as well as uncoordinated
interference. In this article, we review recent advanced coordinated
beamforming (CB) schemes as alternatives, requiring less overhead than JT CoMP
while achieving good performance in realistic conditions. By stipulating that,
in certain LTE scenarios of increasing interest, uncoordinated interference
constitutes a major factor in the performance of CoMP techniques at large, we
hereby assess the resilience of the state-of-the-art CB to uncoordinated
interference. We also describe how these techniques can leverage the latest
specifications of current cellular networks, and how they may perform when we
consider standardized feedback and coordination. This allows us to identify
some key roadblocks and research directions to address as LTE evolves towards
the future of mobile communications.Comment: 16 pages, 6 figures, accepted to IEEE Communications Magazin
Six nouvelles espèces de Pittosporum (Pittosporaceae) à fruits ornementés de Nouvelle-Calédonie
Diagonals of rational functions, pullbacked 2F1 hypergeometric functions and modular forms (unabrigded version)
We recall that diagonals of rational functions naturally occur in lattice
statistical mechanics and enumerative combinatorics. We find that a
seven-parameter rational function of three variables with a numerator equal to
one (reciprocal of a polynomial of degree two at most) can be expressed as a
pullbacked 2F1 hypergeometric function. This result can be seen as the simplest
non-trivial family of diagonals of rational functions. We focus on some
subcases such that the diagonals of the corresponding rational functions can be
written as a pullbacked 2F1 hypergeometric function with two possible rational
functions pullbacks algebraically related by modular equations, thus showing
explicitely that the diagonal is a modular form. We then generalise this result
to eight, nine and ten parameters families adding some selected cubic terms at
the denominator of the rational function defining the diagonal. We finally show
that each of these previous rational functions yields an infinite number of
rational functions whose diagonals are also pullbacked 2F1 hypergeometric
functions and modular forms.Comment: 39 page
Quantum electrodynamics of relativistic bound states with cutoffs
We consider an Hamiltonian with ultraviolet and infrared cutoffs, describing
the interaction of relativistic electrons and positrons in the Coulomb
potential with photons in Coulomb gauge. The interaction includes both
interaction of the current density with transversal photons and the Coulomb
interaction of charge density with itself. We prove that the Hamiltonian is
self-adjoint and has a ground state for sufficiently small coupling constants.Comment: To appear in "Journal of Hyperbolic Differential Equation
Digitization of multistep organic synthesis in reactionware for on-demand pharmaceuticals
Chemical manufacturing is often done at large facilities that require a sizable capital investment and then produce key compounds for a finite period. We present an approach to the manufacturing of fine chemicals and pharmaceuticals in a self-contained plastic reactionware device. The device was designed and constructed by using a chemical to computer-automated design (ChemCAD) approach that enables the translation of traditional bench-scale synthesis into a platform-independent digital code. This in turn guides production of a three-dimensional printed device that encloses the entire synthetic route internally via simple operations. We demonstrate the approach for the γ-aminobutyric acid receptor agonist, (±)-baclofen, establishing a concept that paves the way for the local manufacture of drugs outside of specialist facilities
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