25,980 research outputs found
Super-Resolution in Phase Space
This work considers the problem of super-resolution. The goal is to resolve a
Dirac distribution from knowledge of its discrete, low-pass, Fourier
measurements. Classically, such problems have been dealt with parameter
estimation methods. Recently, it has been shown that convex-optimization based
formulations facilitate a continuous time solution to the super-resolution
problem. Here we treat super-resolution from low-pass measurements in Phase
Space. The Phase Space transformation parametrically generalizes a number of
well known unitary mappings such as the Fractional Fourier, Fresnel, Laplace
and Fourier transforms. Consequently, our work provides a general super-
resolution strategy which is backward compatible with the usual Fourier domain
result. We consider low-pass measurements of Dirac distributions in Phase Space
and show that the super-resolution problem can be cast as Total Variation
minimization. Remarkably, even though are setting is quite general, the bounds
on the minimum separation distance of Dirac distributions is comparable to
existing methods.Comment: 10 Pages, short paper in part accepted to ICASSP 201
SAR-Based Vibration Estimation Using the Discrete Fractional Fourier Transform
A vibration estimation method for synthetic aperture radar (SAR) is presented based on a novel application of the discrete fractional Fourier transform (DFRFT). Small vibrations of ground targets introduce phase modulation in the SAR returned signals. With standard preprocessing of the returned signals, followed by the application of the DFRFT, the time-varying accelerations, frequencies, and displacements associated with vibrating objects can be extracted by successively estimating the quasi-instantaneous chirp rate in the phase-modulated signal in each subaperture. The performance of the proposed method is investigated quantitatively, and the measurable vibration frequencies and displacements are determined. Simulation results show that the proposed method can successfully estimate a two-component vibration at practical signal-to-noise levels. Two airborne experiments were also conducted using the Lynx SAR system in conjunction with vibrating ground test targets. The experiments demonstrated the correct estimation of a 1-Hz vibration with an amplitude of 1.5 cm and a 5-Hz vibration with an amplitude of 1.5 mm
Iterative Time-Varying Filter Algorithm Based on Discrete Linear Chirp Transform
Denoising of broadband non--stationary signals is a challenging problem in
communication systems. In this paper, we introduce a time-varying filter
algorithm based on the discrete linear chirp transform (DLCT), which provides
local signal decomposition in terms of linear chirps. The method relies on the
ability of the DLCT for providing a sparse representation to a wide class of
broadband signals. The performance of the proposed algorithm is compared with
the discrete fractional Fourier transform (DFrFT) filtering algorithm.
Simulation results show that the DLCT algorithm provides better performance
than the DFrFT algorithm and consequently achieves high quality filtering.Comment: 6 pages, conference pape
Wavelet entropy of stochastic processes
We compare two different definitions for the wavelet entropy associated to
stochastic processes. The first one, the Normalized Total Wavelet Entropy
(NTWS) family [Phys. Rev. E 57 (1998) 932; J. Neuroscience Method 105 (2001)
65; Physica A (2005) in press] and a second introduced by Tavares and Lucena
[Physica A 357 (2005)~71]. In order to understand their advantages and
disadvantages, exact results obtained for fractional Gaussian noise (-1<alpha<
1) and the fractional Brownian motion (1 < alpha < 3) are assessed. We find out
that NTWS family performs better as a characterization method for these
stochastic processes.Comment: 12 pages, 4 figures, submitted to Physica
Quasi-periodic pulse amplitude modulation in the accreting millisecond pulsar IGR J00291+5934
We introduce a new method for analysing the aperiodic variability of coherent
pulsations in accreting millisecond X-ray pulsars. Our method involves applying
a complex frequency correction to the time-domain light curve, allowing for the
aperiodic modulation of the pulse amplitude to be robustly extracted in the
frequency domain. We discuss the statistical properties of the resulting
modulation spectrum and show how it can be correlated with the non-pulsed
emission to determine if the periodic and aperiodic variability are coupled
processes. Using this method, we study the 598.88 Hz coherent pulsations of the
accreting millisecond X-ray pulsar IGR J00291+5934 as observed with the Rossi
X-ray Timing Explorer and XMM-Newton. We demonstrate that our method easily
confirms the known coupling between the pulsations and a strong 8 mHz QPO in
XMM-Newton observations. Applying our method to the RXTE observations, we
further show, for the first time, that the much weaker 20 mHz QPO and its
harmonic are also coupled the pulsations. We discuss the implications of this
coupling and indicate how it may be used to extract new information on the
underlying accretion process.Comment: 12 pages, 7 figures, 1 table. Accepted for publication in Ap
- …