The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform

Sergio Barbarossa - One of the best experts on this subject based on the ideXlab platform.

  • Small Perturbation Analysis of Network Topologies
    2018 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2018
    Co-Authors: Elena Ceci, Sergio Barbarossa
    Abstract:

    The goal of this paper is to derive a small perturbation analysis for networks subject to random changes of a small number of edges. Small perturbation Theory allows us to derive, albeit approximate, closed form expressions that make possible the theoretical statistical characterization of the network topology changes. The analysis is instrumental to formulate a graph-based optimization algorithm, which is robust against edge failures. In particular, we focus on the optimal allocation of the overall transmit powers in wireless communication networks subject to fading, aimed at minimizing the variation of the network connectivity, subject to a constraint on the overall power necessary to maintain network connectivity.

  • ICASSP - Small Perturbation Analysis of Network Topologies
    2018 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2018
    Co-Authors: Elena Ceci, Sergio Barbarossa
    Abstract:

    The goal of this paper is to derive a small perturbation analysis for networks subject to random changes of a small number of edges. Small perturbation Theory allows us to derive, albeit approximate, closed form expressions that make possible the theoretical statistical characterization of the network topology changes. The analysis is instrumental to formulate a graph-based optimization algorithm, which is robust against edge failures. In particular, we focus on the optimal allocation of the overall transmit powers in wireless communication networks subject to fading, aimed at minimizing the variation of the network connectivity, subject to a constraint on the overall power necessary to maintain network connectivity.

Elena Ceci - One of the best experts on this subject based on the ideXlab platform.

  • Small Perturbation Analysis of Network Topologies
    2018 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2018
    Co-Authors: Elena Ceci, Sergio Barbarossa
    Abstract:

    The goal of this paper is to derive a small perturbation analysis for networks subject to random changes of a small number of edges. Small perturbation Theory allows us to derive, albeit approximate, closed form expressions that make possible the theoretical statistical characterization of the network topology changes. The analysis is instrumental to formulate a graph-based optimization algorithm, which is robust against edge failures. In particular, we focus on the optimal allocation of the overall transmit powers in wireless communication networks subject to fading, aimed at minimizing the variation of the network connectivity, subject to a constraint on the overall power necessary to maintain network connectivity.

  • ICASSP - Small Perturbation Analysis of Network Topologies
    2018 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2018
    Co-Authors: Elena Ceci, Sergio Barbarossa
    Abstract:

    The goal of this paper is to derive a small perturbation analysis for networks subject to random changes of a small number of edges. Small perturbation Theory allows us to derive, albeit approximate, closed form expressions that make possible the theoretical statistical characterization of the network topology changes. The analysis is instrumental to formulate a graph-based optimization algorithm, which is robust against edge failures. In particular, we focus on the optimal allocation of the overall transmit powers in wireless communication networks subject to fading, aimed at minimizing the variation of the network connectivity, subject to a constraint on the overall power necessary to maintain network connectivity.

Marc Saillard - One of the best experts on this subject based on the ideXlab platform.

  • Modelization of the Scattering of Electromagnetic Waves from the Ocean Surface
    Progress in Electromagnetics Research-pier, 2020
    Co-Authors: G. Soriano, Marc Saillard
    Abstract:

    In this paper, two models for the solution of the electromagnetic bistatic scattering from sea surface are suggested. A rigorous formalism leading to weakly singular integral equations is presented, as well as the surface impedance approximation for low penetrable media and the beam simulation method to synthesize incident beams with arbitrary size. This rigorous integral method is used to test first order approximations, and it is shown that the Small Slope Approximation is very accurate in predicting the scattering crosssection from the high spatial frequencies of the sea surface. This result led us to suggest an improvement of the classical two-scale model, consisting in replacing the small perturbation Theory by the small slope approximation. This change allows the cut-off spatial frequency to be shifted so that the use of geometrical Optics is restricted to the large scales.

  • A Two-Step Procedure for Characterizing Obstacles Under a Rough Surface From Bistatic Measurements
    IEEE Transactions on Geoscience and Remote Sensing, 2007
    Co-Authors: Octavien Cmielewski, HervÉ Tortel, AmÉlie Litman, Marc Saillard
    Abstract:

    A two-step electromagnetic detection procedure is proposed to characterize a dielectric obstacle buried at low depth under a rough surface from single-frequency and multistatic data. First, we have developed, in the framework of the small perturbation Theory, a correlation procedure of the scattered field, which enables us to recover an estimation of the roughness profile. This method is tested for various cases with synthetic data provided by a rigorous boundary integral solver. Second, the obtained surface profile is introduced into the numerical simulation due to a finite-element code. An iterative process is then used, based on a level-set formulation, to obtain the shape of the buried target. The influence of the prior step on the accuracy of the reconstruction of the target is studied via various criteria and for different configurations.

  • Electromagnetic scattering from multi-scale rough surfaces
    Waves in Random Media, 1997
    Co-Authors: Charles-antoine Guérin, Matthias Holschneider, Marc Saillard
    Abstract:

    Abstract It is shown that the wavelet correlation dimension is a very relevant quantity for the characterization of rough surfaces by remote sensing means. First, the concept of correlation length is generalized to surfaces with wide power spectrum. Second, it is demonstrated that, in the framework of the Small-Perturbation Theory, the wavelet correlation dimension can be retrieved from a knowledge of the backscattered cross section for a discrete set of frequencies. Rigorous numerical experiments confirm these predictions, and in the last section an experimental scheme for a straightforward derivation of the wavelet correlation dimension is proposed.

M.a. Valente - One of the best experts on this subject based on the ideXlab platform.

  • Microwaves dielectric properties of Y 3 Fe 5 O 12 -CaCu 3 Ti 4 O 12 composites
    2011 SBMO IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC 2011), 2011
    Co-Authors: K. D. A. Sabóia, Luís Cadillon Costa, H. T. Girão, A. S. B. Sombra, M. P. F. Graça, F. Amaral, M.a. Valente
    Abstract:

    A study of the effect of the presence of Y 3 Fe 5 O 12 (YIG) in the dielectric properties of the CaCu 3 Ti 4 O 12 (CCTO) is presented. The samples were prepared by the solid state method. Mechanical alloying followed by the solid state procedure had been successfully used to produce powders of CCTO and YIG to be used in the composites. We also look at the effect of the grain size of the YIG and CCTO in the final properties of the composite. The samples were analyzed using X-Ray diffraction and scanning electron microscopy (SEM). Dielectric permittivity had been measured at 2.7 and 5.0 GHz, using the small perturbation Theory.

  • Microwaves dielectric properties of Y3Fe5O12-CaCu3Ti4O12 composites
    2011 SBMO IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC 2011), 2011
    Co-Authors: K. D. A. Sabóia, H. T. Girão, A. S. B. Sombra, M. P. F. Graça, L. C. Costa, F. Amaral, M.a. Valente
    Abstract:

    A study of the effect of the presence of Y3Fe5O12 (YIG) in the dielectric properties of the CaCu3Ti4O12 (CCTO) is presented. The samples were prepared by the solid state method. Mechanical alloying followed by the solid state procedure had been successfully used to produce powders of CCTO and YIG to be used in the composites. We also look at the effect of the grain size of the YIG and CCTO in the final properties of the composite. The samples were analyzed using X-Ray diffraction and scanning electron microscopy (SEM). Dielectric permittivity had been measured at 2.7 and 5.0 GHz, using the small perturbation Theory.

  • Resonant cavity for the measurement of microwave magnetic permeability using the small perturbation Theory
    Microwave and Optical Technology Letters, 2008
    Co-Authors: D. X. Gouveia, Luís Cadillon Costa, M.a. Valente
    Abstract:

    The design of a rectangular cavity resonator implies to solve the Maxwell equations inside that cavity, respecting the boundary conditions. The resonance frequencies appear as conditions in the solutions of those equations. When a small piece of a magnetic material is introduced in the cavity, the resonance frequency and the quality factor changes. These effects can be used in the measurement of the permeability of the material. The relations are derived from the perturbation Theory of resonant cavities and are simple when we consider only the first-order perturbation in the magnetic field caused by the sample. This is guaranteed when linearity exists between the measured perturbation and the volume of the inserted sample. In this work, a resonant cavity to measure the magnetic permeability of a material, at 2.16 GHz, was developed and characterized. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 399–402, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23098

Leung Tsang - One of the best experts on this subject based on the ideXlab platform.

  • random rough surface effects in interconnects studied by small perturbation Theory in waveguide model
    Electrical Performance of Electronic Packaging, 2011
    Co-Authors: Ruihua Ding, Leung Tsang, Henning Braunisch
    Abstract:

    We study the effects of random roughness on wave propagation in a parallel plate metallic waveguide with finite conductivity. The rough surface is three dimensional (3D) with roughness heights varying in both horizontal directions. Integral equations are obtained from the extinction theorem formulated with layered medium Green's function. The second order small perturbation method is then applied to solve the integral equations. A closed form expression for the coherent wave is derived, which is expressed in terms of a three-fold Sommerfeld type integral due to the waveguide structure. Approximate methods are applied to calculate the Sommerfeld integral. The coherent wave enhancement factors of absorption are computed. The results for waveguides are also compared with the results obtained for a plane wave incident on a metal surface with 3D roughness. Results are illustrated for 3D roughness with a variety of power spectra. It is shown that enhancement factors for a waveguide are larger than that of the plane wave case.

  • Conical diffraction of electromagnetic waves from one-dimensional lossy dielectric rough surfaces by using the wavelet transform
    IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174), 1998
    Co-Authors: Chi Hou Chan, Leung Tsang
    Abstract:

    Scattering by a random rough surface is an important problem in remote sensing. The classical analytic techniques of Kirchhoff approximation and small perturbation Theory are limited in domains of validity. Recently, the authors have developed a fast computational technique based on the banded matrix iterative approach/canonical grid method; however, the matrix-vector multiplication still dominates the computational efficiency if the bandwidth is very large due to the significant strong near-interactions involved. To enhance the solving performance, a screening window in conjunction with the wavelet transform matrix is proposed so as to reduce the required storage and computational CPU time. It is noted that the wavelet-transformed matrix for each sub-matrix is implemented only once. Based on the idea of multiresolution analysis, the matrix-vector multiplication in an iterative solver is then efficiently evaluated for its higher sparsity. Typical examples of the conical diffraction from one-dimensional lossy dielectric rough surfaces are therefore investigated to validate the proposed method and applied to passive microwave remote sensing problems.

  • monte carlo simulations of scattering of waves by a random rough surface with the finite element method and the finite difference method
    Microwave and Optical Technology Letters, 1990
    Co-Authors: Leung Tsang, Chi Hou Chan, Akira Ishimaru
    Abstract:

    The finite element and the finite difference methods are applied to Monte Carlo simulations of random rough surface scattering. The advantages of these methods are the banded nature of matrix and the reduction of computer time. These results are also compared with those of Kirchhoff approximation and those of small perturbation Theory when applicable.