Search results for "algorithm"

A measurement-based channel model for vehicular communications in tunnels

2014

Wireless Communications and Networking Conference (WCNC), 2014 IEEE, Istanbul, TURQUIE, 06-/04/2014 - 09/04/2014; In this paper, we present a new version of the iterative nonlinear least square approximation (INLSA) algorithm for the design of measurement-based channel simulators. The proposed method aims to match the time-variant impulse response (TVIR) of the simulation model to that of the measured channel. The propagation delays are discerned directly from the measurements, whereas the gains, the Doppler frequencies, and the phases are computed iteratively by minimizing a matching error norm. We evaluate the performance of the proposed method in terms of the approximation of the transfe…

2018

Electrocardiographic imaging (ECGI) strongly relies on a priori assumptions and additional information to overcome ill-posedness. The major challenge of obtaining good reconstructions consists in finding ways to add information that effectively restricts the solution space without violating properties of the sought solution. In this work, we attempt to address this problem by constructing a spatio-temporal basis of body surface potentials (BSP) from simulations of many focal excitations. Measured BSPs are projected onto this basis and reconstructions are expressed as linear combinations of corresponding transmembrane voltage (TMV) basis vectors. The novel method was applied to simulations o…

Sparse multipath channels: Modelling, analysis, and simulation

2013

A sparse multipath channel is characterized by a small number of randomly distributed scatterers. This study proposes a methodology for the modelling of sparse multipath channels. The new methodology is then used to develop a sparse narrowband multipath channel model by applying the sum-of-cisoids (SOC) principle. The statistical properties of the presented sparse SOC multipath channel model are studied. Analytical expressions are derived for the mean value, variance, autocorrelation function (ACF) and cross-correlation function (CCF) of the complex channel gain, as well as for the probability density function (PDF) of the envelope. Our study shows that mobile radio channels behave in spars…

A limited feedback scheme based on spatially correlated channels for coordinated multipoint systems

2012

High spectral efficiency can be achieved in the downlink of multi-antenna coordinated multi-point systems provided that the multiuser interference is appropriately managed at the transmitter side. For this sake, downlink channel information needs to be sent back by the users, thus reducing the rate available at the uplink channel. The amount and type of feedback information required has been extensively studied and many limited feedback schemes have been proposed lately. A common pattern to all of them is that achieving low rates of feedback information is possible at the cost of increasing complexity at the user side and, sometimes, assuming that some statistics of the channel are known. I…

Special factors and the combinatorics of suffix and factor automata

2011

AbstractThe suffix automaton (resp. factor automaton) of a finite word w is the minimal deterministic automaton recognizing the set of suffixes (resp. factors) of w. We study the relationships between the structure of the suffix and factor automata and classical combinatorial parameters related to the special factors of w. We derive formulae for the number of states of these automata. We also characterize the languages LSA and LFA of words having respectively suffix automaton and factor automaton with the minimal possible number of states.

Echocardiographic Image Analysis Based on the Evaluation of first Order Speckle Statistics

1992

Basic theoretical considerations on the statistical properties of the speckle phenomenon indicate that a conventional quantization (intervals of uniform width) of the received and envelope detected RF — signal is not adequate. We therefore propose a quantization scheme which is based on the application of quantization intervals producing always the same confidence level (adaptive quantization). The advantages are: homogenous distribution of speckle noise reduction to about 10 – 20 significant quantization levels (with neglectable loss of morphological information) quantitative measure (confidence level) of the separability of regions represented with different quantization levels. We furthe…

Data repeatability and acquisition techniques for Time-Domain Spectral Induced Polarization

2013

The Time Domain Induced Polarization (TDIP) technique is widely used in applied geophysics, particularly for environmental issues, for instance for delineating landfills or detecting leachate percolation. Because the reliability of IP data remains an issue at the field scale, this paper deals with the factors controlling data quality and compares different arrays and acquisition parameters for optimal collection of data in the field. The first part focuses on repeatability experiments carried out in the former Horlokke landfill (Denmark), in order to infer the degree of which a signal can be reproduced over time. Results show a good repeatability, with on average less than 10% of difference…

Analytical evaluation of structural response for stationary multicorrelated input

1990

Abstract An analytical procedure is presented which can drastically reduce computational effort in the evaluation of the spectral moments of an elastic linear multi-degree-of-freedom system subjected to a stationary multicorrelated input process. The reduction in computer time is possible since the cross-spectral moments of two oscillators can be obtained in recursive manner as a linear combination of the spectral moment of each oscillator taken separately, which is evaluated by means of a very fast numerical technique.

Delineation of Malignant Skin Tumors by Hyperspectral Imaging

2018

This chapter outlines a new non-invasive method for delineation of skin lesions such as lentigo maligna and lentigo maligna melanoma. The method is based on the analysis of hyperspectral (HS) images taken in vivo before surgical excision of the lesions. For this, characteristic features of the spectral signatures of diseased pixels and healthy pixels are extracted, which combine the intensities in a few selected wavebands with the coefficients of the wavelet frame transforms of the spectral curves. To reduce dimensionality and to reveal the internal structure of the datasets, the diffusion maps (DM) technique is applied. The averaged Nearest Neighbor and the Classification and Regression Tr…

Guest-to-host proton transfer in melatonin-beta-cyclodextrin inclusion complex by ionspray, fast atom bombardment and tandem mass spectrometry.

2001

Ionspray (IS) and fast atom bombardment (FAB) positive ionization mass spectrometry (MS) of 1:1 β-cyclodextrin (β-CD)-melatonin (MLT) host-guest complex allowed the detection of gaseous protonated 1:1 β-CD-MLT. Tandem MS collision-induced dissociation (CID) of such protonated 1:1 β-CD-MLT species showed the proton (charge) to be retained to a significant extent by the host and by its cage fragmentation products, in spite of the higher proton affinity of MLT with respect to that of β-CD. This requires an endothermic guest-to-host proton transfer to occur within the gaseous association. Collisional activation could be accounted for by the promotion of such an endothermic process; however…