Abstract-Collaborative beamforming has already demonstrated its potential of significant power savings in distributed sensor networks. In collaborative beamforming, the antennas of the sensor nodes form a distributed antenna array in an effort to direct the radiated energy to the desired direction and thus increase the overall power efficiency of the network. Existing studies, however, have not addressed several major design issues: how to (1) optimally select a subset of radiating sensors for a given receiver to obtain optimal beamforming performance, (2) alternate among subsets of radiating sensors to prolong the lifetime of the sensors and robustness of network connection to the receiver, and (3) do so in the presence of synchronization and localization uncertainties. In this paper, we first show that the problem of selecting the subset of sensors that achieve optimal beamforming performance is NP-complete. We then propose a heuristic algorithm with complexity O(M log M ), where M is the total number of distributed sensors, that simultaneously addresses the above three issues. In particular, we demonstrate its effectiveness in realistic scenarios with synchronization and localization errors. Further, we show that real-time grouping can be achieved even when thousands of sensors are spread over large distances of over 1000 wavelengths.
Abstract-The scattering of electromagnetic spherical wave by a perfectly conducting circular disk is studied by using the method of Kobayashi Potential (abbreviated as KP method). The formulation of the problem yields the dual integral equations (DIE). The spherical wave is produced by an arbitrarily oriented dipole. The unknowns are the induced surface current (or magnetic field) and the tangential components of the electric field on the disk. The solution for the surface current is expanded in terms of a set of functions which satisfy one of a pair (equations for the magnetic field) of Maxwell equations and the required edge condition on the surface of the disk. At this stage we have used the vector Hankel transform. Applying the projection solves the rest of the pair of equations. Thus the problem reduces to the matrix equations for the expansion coefficients. The matrix elements are given in terms of the infinite integrals with a single variable and these may be transformed into infinite series that are convenient for numerical computation. The far field patterns of the scattered wave are computed and compared with those computed based on the physical optics approximation. The agreement between them is fairly good.
An exact transition matrix was formulated for electromagnetic scattering by a sphere made of a magnetoelectrically gyrotropic material with unit relative permittivity and relative permeability. The total scattering and forward scattering efficiencies are lower when the magnetoelectric gyrotropy vector of the sphere is either coparallel or antiparallel to the electric field or magnetic field of an incident plane wave than when the magnetoelectric gyrotropy vector is parallel to the propagation vector of the incident plane wave. Backscattering is absent when the propagation vector is either coparallel or antiparallel to the magnetoelectric gyrotropy vector.
Abstract-In this investigation, scattering from a circular disk with surface impedance has been studied rigorously. The method of analysis is Kobayashi Potential (KP). The mathematical formulation yields the dual integral equations (DIEs). These DIEs are solved by using the discontinuous properties of Weber-Schafheitlin's integral. After applying the boundary conditions and projection, the resulting expressions, finally, reduce to matrix equations for expansion coefficients. The matrix elements are in the form of infinite integrals with single variable. These are then used to compute the values of expansion coefficients. The far field patterns of the scattered wave are computed for different incident angles and surface impedances for both E-and H-polarizations. To verify the results, we have computed the solution based on the physical optics approximation. The agreement between them is fairly good.
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