37,520 research outputs found
Finding Structural Information of RF Power Amplifiers using an Orthogonal Non-Parametric Kernel Smoothing Estimator
A non-parametric technique for modeling the behavior of power amplifiers is
presented. The proposed technique relies on the principles of density
estimation using the kernel method and is suited for use in power amplifier
modeling. The proposed methodology transforms the input domain into an
orthogonal memory domain. In this domain, non-parametric static functions are
discovered using the kernel estimator. These orthogonal, non-parametric
functions can be fitted with any desired mathematical structure, thus
facilitating its implementation. Furthermore, due to the orthogonality, the
non-parametric functions can be analyzed and discarded individually, which
simplifies pruning basis functions and provides a tradeoff between complexity
and performance. The results show that the methodology can be employed to model
power amplifiers, therein yielding error performance similar to
state-of-the-art parametric models. Furthermore, a parameter-efficient model
structure with 6 coefficients was derived for a Doherty power amplifier,
therein significantly reducing the deployment's computational complexity.
Finally, the methodology can also be well exploited in digital linearization
techniques.Comment: Matlab sample code (15 MB):
https://dl.dropboxusercontent.com/u/106958743/SampleMatlabKernel.zi
Generalized Approximate Survey Propagation for High-Dimensional Estimation
In Generalized Linear Estimation (GLE) problems, we seek to estimate a signal
that is observed through a linear transform followed by a component-wise,
possibly nonlinear and noisy, channel. In the Bayesian optimal setting,
Generalized Approximate Message Passing (GAMP) is known to achieve optimal
performance for GLE. However, its performance can significantly degrade
whenever there is a mismatch between the assumed and the true generative model,
a situation frequently encountered in practice. In this paper, we propose a new
algorithm, named Generalized Approximate Survey Propagation (GASP), for solving
GLE in the presence of prior or model mis-specifications. As a prototypical
example, we consider the phase retrieval problem, where we show that GASP
outperforms the corresponding GAMP, reducing the reconstruction threshold and,
for certain choices of its parameters, approaching Bayesian optimal
performance. Furthermore, we present a set of State Evolution equations that
exactly characterize the dynamics of GASP in the high-dimensional limit
Tsallis non-extensive statistics, intermittent turbulence, SOC and chaos in the solar plasma. Part two: Solar Flares dynamics
In the second part of this study and similarly with part one, the nonlinear
analysis of the solar flares index is embedded in the non-extensive statistical
theory of Tsallis [1]. The triplet of Tsallis, as well as the correlation
dimension and the Lyapunov exponent spectrum were estimated for the SVD
components of the solar flares timeseries. Also the multifractal scaling
exponent spectrum, the generalized Renyi dimension spectrum and the spectrum of
the structure function exponents were estimated experimentally and
theoretically by using the entropy principle included in Tsallis non extensive
statistical theory, following Arimitsu and Arimitsu [2]. Our analysis showed
clearly the following: a) a phase transition process in the solar flare
dynamics from high dimensional non Gaussian SOC state to a low dimensional also
non Gaussian chaotic state, b) strong intermittent solar corona turbulence and
anomalous (multifractal) diffusion solar corona process, which is strengthened
as the solar corona dynamics makes phase transition to low dimensional chaos:
c) faithful agreement of Tsallis non equilibrium statistical theory with the
experimental estimations of i) non-Gaussian probability distribution function,
ii) multifractal scaling exponent spectrum and generalized Renyi dimension
spectrum, iii) exponent spectrum of the structure functions estimated for the
sunspot index and its underlying non equilibrium solar dynamics. e) The solar
flare dynamical profile is revealed similar to the dynamical profile of the
solar convection zone as far as the phase transition process from SOC to chaos
state. However the solar low corona (solar flare) dynamical characteristics can
be clearly discriminated from the dynamical characteristics of the solar
convection zone.Comment: 21 pages, 11 figures, 1 table. arXiv admin note: substantial text
overlap with arXiv:1201.649
Tsallis non-extensive statistics, intermittent turbulence, SOC and chaos in the solar plasma. Part one: Sunspot dynamics
In this study, the nonlinear analysis of the sunspot index is embedded in the
non-extensive statistical theory of Tsallis. The triplet of Tsallis, as well as
the correlation dimension and the Lyapunov exponent spectrum were estimated for
the SVD components of the sunspot index timeseries. Also the multifractal
scaling exponent spectrum, the generalized Renyi dimension spectrum and the
spectrum of the structure function exponents were estimated experimentally and
theoretically by using the entropy principle included in Tsallis non extensive
statistical theory, following Arimitsu and Arimitsu. Our analysis showed
clearly the following: a) a phase transition process in the solar dynamics from
high dimensional non Gaussian SOC state to a low dimensional non Gaussian
chaotic state, b) strong intermittent solar turbulence and anomalous
(multifractal) diffusion solar process, which is strengthened as the solar
dynamics makes phase transition to low dimensional chaos in accordance to
Ruzmaikin, Zeleny and Milovanov studies c) faithful agreement of Tsallis non
equilibrium statistical theory with the experimental estimations of i)
non-Gaussian probability distribution function, ii) multifractal scaling
exponent spectrum and generalized Renyi dimension spectrum, iii) exponent
spectrum of the structure functions estimated for the sunspot index and its
underlying non equilibrium solar dynamics.Comment: 40 pages, 11 figure
Sampling and Super-resolution of Sparse Signals Beyond the Fourier Domain
Recovering a sparse signal from its low-pass projections in the Fourier
domain is a problem of broad interest in science and engineering and is
commonly referred to as super-resolution. In many cases, however, Fourier
domain may not be the natural choice. For example, in holography, low-pass
projections of sparse signals are obtained in the Fresnel domain. Similarly,
time-varying system identification relies on low-pass projections on the space
of linear frequency modulated signals. In this paper, we study the recovery of
sparse signals from low-pass projections in the Special Affine Fourier
Transform domain (SAFT). The SAFT parametrically generalizes a number of well
known unitary transformations that are used in signal processing and optics. In
analogy to the Shannon's sampling framework, we specify sampling theorems for
recovery of sparse signals considering three specific cases: (1) sampling with
arbitrary, bandlimited kernels, (2) sampling with smooth, time-limited kernels
and, (3) recovery from Gabor transform measurements linked with the SAFT
domain. Our work offers a unifying perspective on the sparse sampling problem
which is compatible with the Fourier, Fresnel and Fractional Fourier domain
based results. In deriving our results, we introduce the SAFT series (analogous
to the Fourier series) and the short time SAFT, and study convolution theorems
that establish a convolution--multiplication property in the SAFT domain.Comment: 42 pages, 3 figures, manuscript under revie
A Reproducing Kernel Perspective of Smoothing Spline Estimators
Spline functions have a long history as smoothers of noisy time series data, and several equivalent kernel representations have been proposed in terms of the Green's function solving the related boundary value problem. In this study we make use of the reproducing kernel property of the Green's function to obtain an hierarchy of time-invariant spline kernels of different order. The reproducing kernels give a good representation of smoothing splines for medium and long length filters, with a better performance of the asymmetric weights in terms of signal passing, noise suppression and revisions. Empirical comparisons of time-invariant filters are made with the classical non linear ones. The former are shown to loose part of their optimal properties when we fixed the length of the filter according to the noise to signal ratio as done in nonparametric seasonal adjustment procedures.equivalent kernels, nonparametric regression, Hilbert spaces, time series filtering, spectral properties
Millisecond and Binary Pulsars as Nature's Frequency Standards. II. Effects of Low-Frequency Timing Noise on Residuals and Measured Parameters
Pulsars are the most stable natural frequency standards. They can be applied
to a number of principal problems of modern astronomy and time-keeping
metrology. The full exploration of pulsar properties requires obtaining
unbiased estimates of the spin and orbital parameters. These estimates depend
essentially on the random noise component being revealed in the residuals of
time of arrivals (TOA). In the present paper, the influence of low-frequency
("red") timing noise with spectral indices from 1 to 6 on TOA residuals,
variances, and covariances of estimates of measured parameters of single and
binary pulsars are studied. In order to determine their functional dependence
on time, an analytic technique of processing of observational data in time
domain is developed which takes into account both stationary and non-stationary
components of noise. Our analysis includes a simplified timing model of a
binary pulsar in a circular orbit and procedure of estimation of pulsar
parameters and residuals under the influence of red noise. We reconfirm that
uncorrelated white noise of errors of measurements of TOA brings on gradually
decreasing residuals, variances and covariances of all parameters. On the other
hand, we show that any red noise causes the residuals, variances, and
covariances of certain parameters to increase with time. Hence, the low
frequency noise corrupts our observations and reduces experimental
possibilities for better tests of General Relativity Theory. We also treat in
detail the influence of a polynomial drift of noise on the residuals and
fitting parameters. Results of the analitic analysis are used for discussion of
a statistic describing stabilities of kinematic and dynamic pulsar time scales.Comment: 40 pages, 1 postscript figure, 1 picture, uses mn.sty, accepted to
Mon. Not. Roy. Astron. So
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