19,511 research outputs found
Distributed Estimation of a Parametric Field Using Sparse Noisy Data
The problem of distributed estimation of a parametric physical field is
stated as a maximum likelihood estimation problem. Sensor observations are
distorted by additive white Gaussian noise. Prior to data transmission, each
sensor quantizes its observation to levels. The quantized data are then
communicated over parallel additive white Gaussian channels to a fusion center
for a joint estimation. An iterative expectation-maximization (EM) algorithm to
estimate the unknown parameter is formulated, and its linearized version is
adopted for numerical analysis. The numerical examples are provided for the
case of the field modeled as a Gaussian bell. The dependence of the integrated
mean-square error on the number of quantization levels, the number of sensors
in the network and the SNR in observation and transmission channels is
analyzed.Comment: to appear at Milcom-201
Limited-Feedback-Based Channel-Aware Power Allocation for Linear Distributed Estimation
This paper investigates the problem of distributed best linear unbiased
estimation (BLUE) of a random parameter at the fusion center (FC) of a wireless
sensor network (WSN). In particular, the application of limited-feedback
strategies for the optimal power allocation in distributed estimation is
studied. In order to find the BLUE estimator of the unknown parameter, the FC
combines spatially distributed, linearly processed, noisy observations of local
sensors received through orthogonal channels corrupted by fading and additive
Gaussian noise. Most optimal power-allocation schemes proposed in the
literature require the feedback of the exact instantaneous channel state
information from the FC to local sensors. This paper proposes a
limited-feedback strategy in which the FC designs an optimal codebook
containing the optimal power-allocation vectors, in an iterative offline
process, based on the generalized Lloyd algorithm with modified distortion
functions. Upon observing a realization of the channel vector, the FC finds the
closest codeword to its corresponding optimal power-allocation vector and
broadcasts the index of the codeword. Each sensor will then transmit its analog
observations using its optimal quantized amplification gain. This approach
eliminates the requirement for infinite-rate digital feedback links and is
scalable, especially in large WSNs.Comment: 5 Pages, 3 Figures, 1 Algorithm, Forty Seventh Annual Asilomar
Conference on Signals, Systems, and Computers (ASILOMAR 2013
Effects of Spatial Randomness on Locating a Point Source with Distributed Sensors
Most studies that consider the problem of estimating the location of a point
source in wireless sensor networks assume that the source location is estimated
by a set of spatially distributed sensors, whose locations are fixed. Motivated
by the fact that the observation quality and performance of the localization
algorithm depend on the location of the sensors, which could be randomly
distributed, this paper investigates the performance of a recently proposed
energy-based source-localization algorithm under the assumption that the
sensors are positioned according to a uniform clustering process. Practical
considerations such as the existence and size of the exclusion zones around
each sensor and the source will be studied. By introducing a novel performance
measure called the estimation outage, it will be shown how parameters related
to the network geometry such as the distance between the source and the closest
sensor to it as well as the number of sensors within a region surrounding the
source affect the localization performance.Comment: 7 Pages, 5 Figures, To appear at the 2014 IEEE International
Conference on Communications (ICC'14) Workshop on Advances in Network
Localization and Navigation (ANLN), Invited Pape
Power Allocation for Distributed BLUE Estimation with Full and Limited Feedback of CSI
This paper investigates the problem of adaptive power allocation for
distributed best linear unbiased estimation (BLUE) of a random parameter at the
fusion center (FC) of a wireless sensor network (WSN). An optimal
power-allocation scheme is proposed that minimizes the -norm of the vector
of local transmit powers, given a maximum variance for the BLUE estimator. This
scheme results in the increased lifetime of the WSN compared to similar
approaches that are based on the minimization of the sum of the local transmit
powers. The limitation of the proposed optimal power-allocation scheme is that
it requires the feedback of the instantaneous channel state information (CSI)
from the FC to local sensors, which is not practical in most applications of
large-scale WSNs. In this paper, a limited-feedback strategy is proposed that
eliminates this requirement by designing an optimal codebook for the FC using
the generalized Lloyd algorithm with modified distortion metrics. Each sensor
amplifies its analog noisy observation using a quantized version of its optimal
amplification gain, which is received by the FC and used to estimate the
unknown parameter.Comment: 6 pages, 3 figures, to appear at the IEEE Military Communications
Conference (MILCOM) 201
Kondo screening cloud in a one dimensional wire: Numerical renormalization group study
We study the Kondo model --a magnetic impurity coupled to a one dimensional
wire via exchange coupling-- by using Wilson's numerical renormalization group
(NRG) technique. By applying an approach similar to which was used to compute
the two impurity problem we managed to improve the bad spatial resolution of
the numerical renormalization group method. In this way we have calculated the
impurity spin - conduction electron spin correlation function which is a
measure of the Kondo compensation cloud whose existence has been a long
standing problem in solid state physics. We also present results on the
temperature dependence of the Kondo correlations.Comment: published versio
Thermal Fluctuations in a Lamellar Phase of a Binary Amphiphile-Solvent Mixture: A Molecular Dynamics Study
We investigate thermal fluctuations in a smectic A phase of an
amphiphile-solvent mixture with molecular dynamics simulations. We use an
idealized model system, where solvent particles are represented by simple
beads, and amphiphiles by bead-and-spring tetramers. At a solvent bead fraction
of 20 % and sufficiently low temperature, the amphiphiles self-assemble into a
highly oriented lamellar phase. Our study aims at comparing the structure of
this phase with the predictions of the elastic theory of thermally fluctuating
fluid membrane stacks [Lei et al., J. Phys. II 5, 1155 (1995)]. We suggest a
method which permits to calculate the bending rigidity and compressibility
modulus of the lamellar stack from the simulation data. The simulation results
are in reasonable agreement with the theory
Mapping the spin-dependent electron reflectivity of Fe and Co ferromagnetic thin films
Spin Polarized Low Energy Electron Microscopy is used as a spin dependent
spectroscopic probe to study the spin dependent specular reflection of a
polarized electron beam from two different magnetic thin film systems:
Fe/W(110) and Co/W(110). The reflectivity and spin-dependent
exchange-scattering asymmetry are studied as a function of electron kinetic
energy and film thickness, as well as the time dependence. The largest value of
the figure of merit for spin polarimetry is observed for a 5 monolayer thick
film of Co/W(110) at an electron kinetic energy of 2eV. This value is 2 orders
of magnitude higher than previously obtained with state of the art Mini-Mott
polarimeter. We discuss implications of our results for the development of an
electron-spin-polarimeter using the exchange-interaction at low energy.Comment: 5 pages, 4 figure
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