6,021 research outputs found
Mobile Localization in Non-Line-of-Sight Using Constrained Square-Root Unscented Kalman Filter
Localization and tracking of a mobile node (MN) in non-line-of-sight (NLOS)
scenarios, based on time of arrival (TOA) measurements, is considered in this
work. To this end, we develop a constrained form of square root unscented
Kalman filter (SRUKF), where the sigma points of the unscented transformation
are projected onto the feasible region by solving constrained optimization
problems. The feasible region is the intersection of several discs formed by
the NLOS measurements. We show how we can reduce the size of the optimization
problem and formulate it as a convex quadratically constrained quadratic
program (QCQP), which depends on the Cholesky factor of the \textit{a
posteriori} error covariance matrix of SRUKF. As a result of these
modifications, the proposed constrained SRUKF (CSRUKF) is more efficient and
has better numerical stability compared to the constrained UKF. Through
simulations, we also show that the CSRUKF achieves a smaller localization error
compared to other techniques and that its performance is robust under different
NLOS conditions.Comment: Under review by IEEE Trans. on Vehicular Technolog
An a posteriori error analysis for an optimal control problem involving the fractional Laplacian
In a previous work, we introduced a discretization scheme for a constrained
optimal control problem involving the fractional Laplacian. For such a control
problem, we derived optimal a priori error estimates that demand the convexity
of the domain and some compatibility conditions on the data. To relax such
restrictions, in this paper, we introduce and analyze an efficient and, under
certain assumptions, reliable a posteriori error estimator. We realize the
fractional Laplacian as the Dirichlet-to-Neumann map for a nonuniformly
elliptic problem posed on a semi--infinite cylinder in one more spatial
dimension. This extra dimension further motivates the design of an posteriori
error indicator. The latter is defined as the sum of three contributions, which
come from the discretization of the state and adjoint equations and the control
variable. The indicator for the state and adjoint equations relies on an
anisotropic error estimator in Muckenhoupt weighted Sobolev spaces. The
analysis is valid in any dimension. On the basis of the devised a posteriori
error estimator, we design a simple adaptive strategy that exhibits optimal
experimental rates of convergence
Adaptive finite element methods for sparse PDE-constrained optimization
We propose and analyze reliable and efficient a posteriori error estimators
for an optimal control problem that involves a nondifferentiable cost
functional, the Poisson problem as state equation and control constraints. To
approximate the solution to the state and adjoint equations we consider a
piecewise linear finite element method whereas three different strategies are
used to approximate the control variable: piecewise constant discretization,
piecewise linear discretization and the so-called variational discretization
approach. For the first two aforementioned solution techniques we devise an
error estimator that can be decomposed as the sum of four contributions: two
contributions that account for the discretization of the control variable and
the associated subgradient, and two contributions related to the discretization
of the state and adjoint equations. The error estimator for the variational
discretization approach is decomposed only in two contributions that are
related to the discretization of the state and adjoint equations. On the basis
of the devised a posteriori error estimators, we design simple adaptive
strategies that yield optimal rates of convergence for the numerical examples
that we perform
Functional error estimators for the adaptive discretization of inverse problems
So-called functional error estimators provide a valuable tool for reliably
estimating the discretization error for a sum of two convex functions. We apply
this concept to Tikhonov regularization for the solution of inverse problems
for partial differential equations, not only for quadratic Hilbert space
regularization terms but also for nonsmooth Banach space penalties. Examples
include the measure-space norm (i.e., sparsity regularization) or the indicator
function of an ball (i.e., Ivanov regularization). The error
estimators can be written in terms of residuals in the optimality system that
can then be estimated by conventional techniques, thus leading to explicit
estimators. This is illustrated by means of an elliptic inverse source problem
with the above-mentioned penalties, and numerical results are provided for the
case of sparsity regularization
Maximum-norm a posteriori error estimates for an optimal control problem
We analyze a reliable and efficient max-norm a posteriori error estimator for
a control-constrained, linear-quadratic optimal control problem. The estimator
yields optimal experimental rates of convergence within an adaptive loop
Adaptive Decision Feedback Detection with Parallel Interference Cancellation and Constellation Constraints for Multi-Antenna Systems
In this paper, a novel low-complexity adaptive decision feedback detection
with parallel decision feedback and constellation constraints (P-DFCC) is
proposed for multiuser MIMO systems. We propose a constrained constellation map
which introduces a number of selected points served as the feedback candidates
for interference cancellation. By introducing a reliability checking, a higher
degree of freedom is introduced to refine the unreliable estimates. The P-DFCC
is followed by an adaptive receive filter to estimate the transmitted symbol.
In order to reduce the complexity of computing the filters with time-varying
MIMO channels, an adaptive recursive least squares (RLS) algorithm is employed
in the proposed P-DFCC scheme. An iterative detection and decoding (Turbo)
scheme is considered with the proposed P-DFCC algorithm. Simulations show that
the proposed technique has a complexity comparable to the conventional parallel
decision feedback detector while it obtains a performance close to the maximum
likelihood detector at a low to medium SNR range.Comment: 10 figure
Dual weighted residual based error control for nonstationary convection-dominated equations: potential or ballast?
Even though substantial progress has been made in the numerical approximation
of convection-dominated problems, its major challenges remain in the scope of
current research. In particular, parameter robust a posteriori error estimates
for quantities of physical interest and adaptive mesh refinement strategies
with proved convergence are still missing. Here, we study numerically the
potential of the Dual Weighted Residual (DWR) approach applied to stabilized
finite element methods to further enhance the quality of approximations. The
impact of a strict application of the DWR methodology is particularly focused
rather than the reduction of computational costs for solving the dual problem
by interpolation or localization.Comment: arXiv admin note: text overlap with arXiv:1803.1064
Data-driven Decision Making with Probabilistic Guarantees (Part 2): Applications of Chance-constrained Optimization in Power Systems
Uncertainties from deepening penetration of renewable energy resources have
posed critical challenges to the secure and reliable operations of future
electric grids. Among various approaches for decision making in uncertain
environments, this paper focuses on chance-constrained optimization, which
provides explicit probabilistic guarantees on the feasibility of optimal
solutions. Although quite a few methods have been proposed to solve
chance-constrained optimization problems, there is a lack of comprehensive
review and comparative analysis of the proposed methods. Part I of this
two-part paper reviews three categories of existing methods to
chance-constrained optimization: (1) scenario approach; (2) sample average
approximation; and (3) robust optimization based methods. Data-driven methods,
which are not constrained by any particular distributions of the underlying
uncertainties, are of particular interest. Part II of this two-part paper
provides a literature review on the applications of chance-constrained
optimization in power systems. Part II also provides a critical comparison of
existing methods based on numerical simulations, which are conducted on
standard power system test cases.Comment: (under review) to be update
Efficient Estimation of Cardiac Conductivities via POD-DEIM Model Order Reduction
Clinical oriented applications of computational electrocardiology require
efficient and reliable identification of patient-specific parameters of
mathematical models based on available measures. In particular, the estimation
of cardiac conductivities in models of potential propagation is crucial, since
they have major quantitative impact on the solution. Available estimates of
cardiac conductivities are significantly diverse in the literature and the
definition of experimental/mathematical estimation techniques is an open
problem with important practical implications in clinics. We have recently
proposed a methodology based on a variational procedure, where the reliability
is confirmed by numerical experiments. In this paper we explore
model-order-reduction techniques to fit the estimation procedure into timelines
of clinical interest. Specifically we consider the Monodomain model and resort
to Proper Orthogonal Decomposition (POD) techniques to take advantage of an
off-line step when solving iteratively the electrocardiological forward model
online. In addition, we perform the Discrete Empirical Interpolation Method
(DEIM) to tackle the nonlinearity of the model. While standard POD techniques
usually fail in this kind of problems, due to the wave-front propagation
dynamics, an educated novel sampling of the parameter space based on the
concept of Domain of Effectiveness introduced here dramatically reduces the
computational cost of the inverse solver by at least 95%
Error estimates for a certain class of elliptic optimal control problems
In this paper, error estimates are presented for a certain class of optimal
control problems with elliptic PDE-constraints. It is assumed that in the cost
functional the state is measured in terms of the energy norm generated by the
state equation. The functional a posteriori error estimates developed by Repin
in late 90's are applied to estimate the cost function value from both sides
without requiring the exact solution of the state equation. Moreover, a lower
bound for the minimal cost functional value is derived. A meaningful error
quantity coinciding with the gap between the cost functional values of an
arbitrary admissible control and the optimal control is introduced. This error
quantity can be estimated from both sides using the estimates for the cost
functional value. The theoretical results are confirmed by numerical tests.Comment: 17 pages, 2 figure
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