14,884 research outputs found
Compressive and Noncompressive Power Spectral Density Estimation from Periodic Nonuniform Samples
This paper presents a novel power spectral density estimation technique for
band-limited, wide-sense stationary signals from sub-Nyquist sampled data. The
technique employs multi-coset sampling and incorporates the advantages of
compressed sensing (CS) when the power spectrum is sparse, but applies to
sparse and nonsparse power spectra alike. The estimates are consistent
piecewise constant approximations whose resolutions (width of the piecewise
constant segments) are controlled by the periodicity of the multi-coset
sampling. We show that compressive estimates exhibit better tradeoffs among the
estimator's resolution, system complexity, and average sampling rate compared
to their noncompressive counterparts. For suitable sampling patterns,
noncompressive estimates are obtained as least squares solutions. Because of
the non-negativity of power spectra, compressive estimates can be computed by
seeking non-negative least squares solutions (provided appropriate sampling
patterns exist) instead of using standard CS recovery algorithms. This
flexibility suggests a reduction in computational overhead for systems
estimating both sparse and nonsparse power spectra because one algorithm can be
used to compute both compressive and noncompressive estimates.Comment: 26 pages, single spaced, 9 figure
Compressive Spectral Clustering
Spectral clustering has become a popular technique due to its high
performance in many contexts. It comprises three main steps: create a
similarity graph between N objects to cluster, compute the first k eigenvectors
of its Laplacian matrix to define a feature vector for each object, and run
k-means on these features to separate objects into k classes. Each of these
three steps becomes computationally intensive for large N and/or k. We propose
to speed up the last two steps based on recent results in the emerging field of
graph signal processing: graph filtering of random signals, and random sampling
of bandlimited graph signals. We prove that our method, with a gain in
computation time that can reach several orders of magnitude, is in fact an
approximation of spectral clustering, for which we are able to control the
error. We test the performance of our method on artificial and real-world
network data.Comment: 12 pages, 2 figure
Compressive Raman imaging with spatial frequency modulated illumination
We report a line scanning imaging modality of compressive Raman technology
with spatial frequency modulated illumination using a single pixel detector. We
demonstrate the imaging and classification of three different chemical species
at line scan rates of 40 Hz
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A sub-Nyquist co-prime sampling music spectral approach for natural frequency identification of white-noise excited structures
Motivated by practical needs to reduce data transmission payloads in wireless sensors for vibration-based monitoring of civil engineering structures, this paper proposes a novel approach for identifying resonant frequencies of white-noise excited structures using acceleration measurements acquired at rates significantly below the Nyquist rate. The approach adopts the deterministic co-prime sub-Nyquist sampling scheme, originally developed to facilitate telecommunication applications, to estimate the autocorrelation function of response acceleration time-histories of low-amplitude white-noise excited structures treated as realizations of a stationary stochastic process. This is achieved without posing any sparsity conditions to the signals. Next, the standard MUSIC algorithm is applied to the estimated autocorrelation function to derive a denoised super-resolution pseudo-spectrum in which natural frequencies are marked by prominent spikes. The accuracy and applicability of the proposed approach is numerically assessed using computer-generated noise-corrupted acceleration time-history data obtained by a simulation-based framework pertaining to a white-noise excited structural system with two closely-spaced modes of vibration carrying the same amount of energy, and a third isolated weakly excited vibrating mode. All three natural frequencies are accurately identified by sampling at as low as 78% below Nyquist rate for signal to noise ratio as low as 0dB (i.e., energy of additive white noise equal to the signal energy), suggesting that the proposed approach is robust and noise-immune while it can reduce data transmission requirements in acceleration wireless sensors for natural frequency identification of engineering structures
The Turbulence Spectrum of Molecular Clouds in the Galactic Ring Survey: A Density-Dependent PCA Calibration
Turbulence plays a major role in the formation and evolution of molecular
clouds. The problem is that turbulent velocities are convolved with the density
of an observed region. To correct for this convolution, we investigate the
relation between the turbulence spectrum of model clouds, and the statistics of
their synthetic observations obtained from Principal Component Analysis (PCA).
We apply PCA to spectral maps generated from simulated density and velocity
fields, obtained from hydrodynamic simulations of supersonic turbulence, and
from fractional Brownian motion fields with varying velocity, density spectra,
and density dispersion. We examine the dependence of the slope of the PCA
structure function, alpha_PCA, on intermittency, on the turbulence velocity
(beta_v) and density (beta_n) spectral indexes, and on density dispersion. We
find that PCA is insensitive to beta_n and to the log-density dispersion
sigma_s, provided sigma_s 2, alpha_PCA increases with sigma_s
due to the intermittent sampling of the velocity field by the density field.
The PCA calibration also depends on intermittency. We derive a PCA calibration
based on fBms with sigma_s<2 and apply it to 367 CO spectral maps of molecular
clouds in the Galactic Ring Survey. The average slope of the PCA structure
function, =0.62\pm0.2, is consistent with the hydrodynamic
simulations and leads to a turbulence velocity exponent =2.06\pm0.6 for
a non-intermittent, low density dispersion flow. Accounting for intermittency
and density dispersion, the coincidence between the PCA slope of the GRS clouds
and the hydrodynamic simulations suggests beta_v~1.9, consistent with both
Burgers and compressible intermittent turbulence
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