80,718 research outputs found
Problems on q-Analogs in Coding Theory
The interest in -analogs of codes and designs has been increased in the
last few years as a consequence of their new application in error-correction
for random network coding. There are many interesting theoretical, algebraic,
and combinatorial coding problems concerning these q-analogs which remained
unsolved. The first goal of this paper is to make a short summary of the large
amount of research which was done in the area mainly in the last few years and
to provide most of the relevant references. The second goal of this paper is to
present one hundred open questions and problems for future research, whose
solution will advance the knowledge in this area. The third goal of this paper
is to present and start some directions in solving some of these problems.Comment: arXiv admin note: text overlap with arXiv:0805.3528 by other author
Fiber link design considerations for cloud-Radio Access Networks
Analog radio over fiber (RoF) links may offer advantages for cloud-Radio Access Networks in terms of component cost, but the behavior of the distortion with large numbers of subcarriers needs to be understood. In this paper, this is presented in terms of the variation between subcarriers. Memory polynomial predistortion is also shown to compensate for RoF and wireless path distortion. Whether for digitized or analog links, it is shown that appropriate framing structure parameters must be used to assure performance, especially of time-division duplex systems
Topological Phase Transition in a Molecular Hamiltonian with Symmetry and Pseudo-Symmetry, Studied through Quantum, Semi-Quantum and Classical Models
The redistribution of energy levels between energy bands is studied for a
family of simple effective Hamiltonians depending on one control parameter and
possessing axial symmetry and energy-reflection symmetry. Further study is made
on the topological phase transition in the corresponding semi-quantum and
completely classical models, and finally the joint spectrum of the two
commuting observables (also called the lattice of quantum states)
is superposed on the image of the energy-momentum map for the classical model.
Through these comparative analyses, mutual correspondence is demonstrated to
exist among the redistribution of energy levels between energy bands for the
quantum Hamiltonian, the modification of Chern numbers of eigenline bundles for
the corresponding semi-quantum Hamiltonian, and the presence of Hamiltonian
monodromy for the complete classical analog. In particular, as far as the band
rearrangement is concerned, a fine agreement is found between the
redistribution of the energy levels described in terms of joint spectrum of
energy and momentum in the full quantum model and the evolution of
singularities of the energy-momentum map of the complete classical model. The
topological phase transition observed in the present semi-quantum and the
complete classical models are analogous to topological phase transitions of
matter
An error-controlled methodology for approximate hierarchical symbolic analysis
Limitations of existing approaches for symbolic analysis of large analog circuits are discussed. To address their solution, a new methodology for hierarchical symbolic analysis is introduced. The combination of a hierarchical modeling technique and approximation strategies, comprising circuit reduction, graph-based symbolic solution of circuit equations and matrix-based error control, provides optimum results in terms of speech and quality of results.European Commission ESPRIT 21812Comisión Interministerial de Ciencia y Tecnología TIC97-058
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