25,883 research outputs found
Sensorless Battery Internal Temperature Estimation using a Kalman Filter with Impedance Measurement
This study presents a method of estimating battery cell core and surface
temperature using a thermal model coupled with electrical impedance
measurement, rather than using direct surface temperature measurements. This is
advantageous over previous methods of estimating temperature from impedance,
which only estimate the average internal temperature. The performance of the
method is demonstrated experimentally on a 2.3 Ah lithium-ion iron phosphate
cell fitted with surface and core thermocouples for validation. An extended
Kalman filter, consisting of a reduced order thermal model coupled with
current, voltage and impedance measurements, is shown to accurately predict
core and surface temperatures for a current excitation profile based on a
vehicle drive cycle. A dual extended Kalman filter (DEKF) based on the same
thermal model and impedance measurement input is capable of estimating the
convection coefficient at the cell surface when the latter is unknown. The
performance of the DEKF using impedance as the measurement input is comparable
to an equivalent dual Kalman filter using a conventional surface temperature
sensor as measurement input.Comment: 10 pages, 9 figures, accepted for publication in IEEE Transactions on
Sustainable Energy, 201
Performance Analysis of Channel Extrapolation in FDD Massive MIMO Systems
Channel estimation for the downlink of frequency division duplex (FDD)
massive MIMO systems is well known to generate a large overhead as the amount
of training generally scales with the number of transmit antennas in a MIMO
system. In this paper, we consider the solution of extrapolating the channel
frequency response from uplink pilot estimates to the downlink frequency band,
which completely removes the training overhead. We first show that conventional
estimators fail to achieve reasonable accuracy. We propose instead to use
high-resolution channel estimation. We derive theoretical lower bounds (LB) for
the mean squared error (MSE) of the extrapolated channel. Assuming that the
paths are well separated, the LB is simplified in an expression that gives
considerable physical insight. It is then shown that the MSE is inversely
proportional to the number of receive antennas while the extrapolation
performance penalty scales with the square of the ratio of the frequency offset
and the training bandwidth. The channel extrapolation performance is validated
through numeric simulations and experimental measurements taken in an anechoic
chamber. Our main conclusion is that channel extrapolation is a viable solution
for FDD massive MIMO systems if accurate system calibration is performed and
favorable propagation conditions are present.Comment: arXiv admin note: substantial text overlap with arXiv:1902.0684
Hybrid 3D Localization for Visible Light Communication Systems
In this study, we investigate hybrid utilization of angle-of-arrival (AOA)
and received signal strength (RSS) information in visible light communication
(VLC) systems for 3D localization. We show that AOA-based localization method
allows the receiver to locate itself via a least squares estimator by
exploiting the directionality of light-emitting diodes (LEDs). We then prove
that when the RSS information is taken into account, the positioning accuracy
of AOA-based localization can be improved further using a weighted least
squares solution. On the other hand, when the radiation patterns of LEDs are
explicitly considered in the estimation, RSS-based localization yields highly
accurate results. In order to deal with the system of nonlinear equations for
RSS-based localization, we develop an analytical learning rule based on the
Newton-Raphson method. The non-convex structure is addressed by initializing
the learning rule based on 1) location estimates, and 2) a newly developed
method, which we refer as random report and cluster algorithm. As a benchmark,
we also derive analytical expression of the Cramer-Rao lower bound (CRLB) for
RSS-based localization, which captures any deployment scenario positioning in
3D geometry. Finally, we demonstrate the effectiveness of the proposed
solutions for a wide range of LED characteristics and orientations through
extensive computer simulations.Comment: Submitted to IEEE/OSA Journal of Lightwave Technology (10 pages, 14
figures
The Morphology of the Thermal Sunyaev-Zel'dovich Sky
At high angular frequencies the thermal Sunyaev-Zel'dovich (tSZ) effect
constitutes the dominant signal in the CMB sky. The tSZ effect is caused by
large scale pressure fluctuations in the baryonic distribution in the Universe
so its statistical properties provide estimates of corresponding properties of
the projected 3D pressure fluctuations. It's power spectrum is a sensitive
probe of the density fluctuations, and the bispectrum can be used to separate
the bias associated with pressure. The bispectrum is often probed with a
one-point real-space analogue, the skewness. In addition to the skewness the
morphological properties, as probed by the well known Minkowski Functionals
(MFs), also require the generalized one-point statistics, which at the lowest
order are identical to the skewness parameters. The concept of generalized
skewness parameters can be extended to define a set of three associated
generalized skew-spectra. We use these skew-spectra to probe the morphology of
the tSZ sky or the y-sky. We show how these power spectra can be recovered from
the data in the presence of arbitrary mask and noise templates using the well
known Pseudo-Cl (PCL) approach for arbitrary beam shape. We also employ an
approach based on the halo model to compute the tSZ bispectrum. The bispectrum
from each of these models is then used to construct the generalized
skew-spectra. We consider the performance of an all-sky survey with Planck-type
noise and compare the results against a noise-free ideal experiment using a
range of smoothing angles. We find that the skew-spectra can be estimated with
very high signal-to-noise ratio from future frequency cleaned tSZ maps that
will be available from experiments such as Planck. This will allow their mode
by mode estimation for a wide range of angular frequencies and will help us to
differentiate them from various other sources of non-Gaussianity.Comment: 18 pages, 10 figures, submitted to MNRA
Sequential Quantiles via Hermite Series Density Estimation
Sequential quantile estimation refers to incorporating observations into
quantile estimates in an incremental fashion thus furnishing an online estimate
of one or more quantiles at any given point in time. Sequential quantile
estimation is also known as online quantile estimation. This area is relevant
to the analysis of data streams and to the one-pass analysis of massive data
sets. Applications include network traffic and latency analysis, real time
fraud detection and high frequency trading. We introduce new techniques for
online quantile estimation based on Hermite series estimators in the settings
of static quantile estimation and dynamic quantile estimation. In the static
quantile estimation setting we apply the existing Gauss-Hermite expansion in a
novel manner. In particular, we exploit the fact that Gauss-Hermite
coefficients can be updated in a sequential manner. To treat dynamic quantile
estimation we introduce a novel expansion with an exponentially weighted
estimator for the Gauss-Hermite coefficients which we term the Exponentially
Weighted Gauss-Hermite (EWGH) expansion. These algorithms go beyond existing
sequential quantile estimation algorithms in that they allow arbitrary
quantiles (as opposed to pre-specified quantiles) to be estimated at any point
in time. In doing so we provide a solution to online distribution function and
online quantile function estimation on data streams. In particular we derive an
analytical expression for the CDF and prove consistency results for the CDF
under certain conditions. In addition we analyse the associated quantile
estimator. Simulation studies and tests on real data reveal the Gauss-Hermite
based algorithms to be competitive with a leading existing algorithm.Comment: 43 pages, 9 figures. Improved version incorporating referee comments,
as appears in Electronic Journal of Statistic
Primordial Non-Gaussianity from a Joint Analysis of Cosmic Microwave Background Temperature and Polarization
We explore a systematic approach to the analysis of primordial
non-Gaussianity using fluctuations in temperature and polarization of the
Cosmic Microwave Background (CMB). Following Munshi & Heavens (2009), we define
a set of power-spectra as compressed forms of the bispectrum and trispectrum
derived from CMB temperature and polarization maps; these spectra compress the
information content of the corresponding full multispectra and can be useful in
constraining early Universe theories. We generalize the standard pseudo-C_l
estimators in such a way that they apply to these spectra involving both spin-0
and spin-2 fields, developing explicit expressions which can be used in the
practical implementation of these estimators. While these estimators are
suboptimal, they are nevertheless unbiased and robust hence can provide useful
diagnostic tests at a relatively small computational cost. We next consider
approximate inverse-covariance weighting of the data and construct a set of
near-optimal estimators based on that approach. Instead of combining all
available information from the entire set of mixed bi- or trispectra, i.e
multispectra describing both temperature and polarization information, we
provide analytical constructions for individual estimators, associated with
particular multispectra. The bias and scatter of these estimators can be
computed using Monte-Carlo techniques. Finally, we provide estimators which are
completely optimal for arbitrary scan strategies and involve inverse covariance
weighting; we present the results of an error analysis performed using a
Fisher-matrix formalism at both the one-point and two-point level.Comment: 25 Pages, 4 Figure
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