3,219 research outputs found
Ndsa measurements between two counter rotating leo satellites: Performance evaluation at global scale in Ku, K and M bands
No full textInternational Geoscience and Remote Sensing Symposium (IGARSS)
2013, Article number 6723551, Pages 3371-3374
2013 33rd IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2013; Melbourne, VIC; Australia; 21 July 2013 through 26 July 2013; Category numberCFP13IGA-ART; Code 102722
Ndsa measurements between two counter rotating leo satellites: Performance evaluation at global scale in Ku, K and M bands (Conference Paper)
Cuccoli, F.a,
Facheris, L.a,
Garzelli, A.c,
Zoppetti, C.b
a CNIT RaSS C/o, Department of Electronics and Telecommunications, University of Florence, Via di Santa Marta 3, 50139 Florence, Italy
b Dept. Information Engineering and Mathematical Sciences, Univ. Siena, Via Roma 56, 53100 Siena, Italy
View references (7)
Abstract
In this work we present and discuss the effects of different scintillation models on the Normalize Differential Spectral Attenuation (NDSA) measurements in a counter-rotating Low Earth Orbiting (LEO) set event at 17, 19, 21, 32, 179 and 182 GHz. Some parameters of the scintillation models used here are computed at global scale using an European Centre for Medium-Range Weather Forecasts (ECMWF) global dataset. The scintillation effects on the NDSA measurements are analyzed in terms of relative error of the their estimation
Impact of multipath on anchor selection strategies for UAV localization in mobile networks
No full textPositioning is gaining increasing importance in mobile systems due to its potential integration with many 5G verticals. In non-terrestrial networks, positioning of aerial vehicles constitutes a crucial element of the communication, control, and applications of these systems. Unmanned aerial vehicles (UAVs) have become strategic actors in this technical and economic trend. A distinctive feature of UAV positioning in mobile networks is that signals from multiple base stations, or anchors, can typically be received and employed for localization, as propagation conditions, including the fundamental line of sight availability, improve with altitude. However, this advantage poses serious issues in terms of computational complexity, channel occupation, and latency unless an appropriate selection of available anchors is performed. In this work, we investigate and discuss several anchor selection strategies under realistic propagation scenarios, with an emphasis on the impact of multipath, according to the 3GPP channel models for aerial vehicles. The application of these strategies to channels affected by multipath using a standard least squares positioning technique reveals interesting properties and design di rections for a feasible solution to the anchor selection problem. Notably, we show that even 3 or 4 well-selected anchors are often sufficient to achieve sub-meter 3D positioning accuracy
3D position error bound for wideband localization systems with application to UAVs
No full textPositioning is a crucial element of the new connected world and its integration with the current and future releases of the mobile system technology has been gaining interest since the introduction of the 5G verticals. In the application layer, positioning provides an additional and, in many cases, a fundamental value for the implementation of services like terrestrial and non-terrestrial vehicles, industrial robots and many other advanced systems. In this work we present a study on the formulation of the 3D Position Error Bound (PEB) based on Time-of-Arrival measures. We extend the analysis of the localization Cramer Rao Bound to the 3D geometry including the impacts of multipath, multiple anchors, clock and position offsets. In addition, we elaborate the result, providing a deeper insight on potential applications of this analytical tool, as positioning of Unmanned Aerial Vehicles in areas covered by 5G signals
The ESA-ANISAP study: estimate of tropospheric scintillation along a LEO-LEO link through high resolution radiosonde data
No full textThis work describes the procedure developed in the framework of the ESA-ANISAP study to obtain, for a given atmospheric profile, an estimate of scintillation effects in a LEO-LEO link. In this procedure, the refractive-index structure constant profiles describing the intensity of turbulence, are derived by applying the vertical gradient approach to high resolution radiosonde data. The fact that turbulence in the free atmosphere is confined to vertically thin layers is accounted for by identifying the turbulent layers through the analysis of the Richardson number profiles. Then, the derived structure constant profiles are inserted into a parametric scintillation model to create a scintillation disturbance estimate consistent with the considered atmospheric profile. In the parametric model, the troposphere is described as a spherically symmetric turbulent medium. Rytov‟s first iteration solution for weak fluctuations is used to derive an expression for two quantities of interest to evaluate the performances of the Normalized Differential Spectral Attenuation for the estimate of the total content of water vapour along the propagation path between two LEO satellite, namely: the variance of amplitude fluctuations of the wave and the correlation between the fluctuations at different frequencies. The influence on these quantities of some turbulence characteristics which are not known with confidence, like the outer scale length and the behaviour of the spectrum in the input range, is also investigated
Tropospheric IWV profiles estimation through multifrequency signal attenuation measurements between two counter-rotating LEO satellites: performance analysis
No full textThe exploitation of multifrequency differential attenuation measurements at microwaves made between two LEO satellites in limb mode is the ground of the NDSA (Normalized Differential Spectral Attenuation) approach for estimating integrated tropospheric water vapor profiles through multifrequency measurements at 17, 19, 21, 179 and 182 GHz, plus 32 GHz for liquid water detection and correction (whenever possible). Such measurements are affected by two kinds of impairments, the first generated by thermal noise at the receiver, the second generated by the signals’ fluctuations due to the variations of the tropospheric refraction index and referred to as scintillation disturbance. Characterizing scintillation for simulating its effects to evaluate NDSA performance is not easy in general: in particular, it is quite hard (and also rather questionable so some extent) to relate the scintillation parameters to a given simulated atmospheric situation. For this reason, in the past years we limited ourselves to evaluate the NDSA performance by accounting for scintillation in a parametric way, independently of the atmospheric context in which simulations were carried out. In this paper, instead, we show the first results of the NDSA performance analysis based on a completely different approach, where the scintillation profiles and parameters are directly derived from the simulated atmospheric context, based on a procedure that starts from high resolution radiosonde data. A brief critical analysis of such an approach is proposed, evidencing some aspects related to the current knowledge of the scintillation spectra and parameters. The NDSA performance analysis based on certain hypotheses for the scintillation characteristics is then shown for some selected simulated atmospheric condition
Impact of tropospheric scintillation in the Ku/K bands on the communications between two LEO satellites in a radio occultation geometry
No full textA theoretical analysis of the impact of clear-air tropospheric scintillation on a radio occultation link between two low Earth orbit satellites in K- and Ku-bands is presented, with particular reference to differential approaches for the measure of the total content of water vapor. The troposphere is described as a spherically symmetric turbulent medium satisfying Kolmogorov theory. Rytov's first iteration solution for weak fluctuations is used to derive an expression for the variance of amplitude fluctuations of the wave as well as their spectrum and the correlation between fluctuations at different frequencies. The validity of the assumptions made and the influence of atmospheric parameters on the quantities of interest are also investigated and discussed. Finally, numerical results are presented to provide an estimate of the level of scintillation-induced disturbances
An assessment of the impact of possible CAP reform scenarios on Romanian agriculture
No full textUsing a simplified model, with key-variable the prices of two different possible scenarios of CAP reform after 2013 (moderate and radical), this paper present a comparison between the price effects of implementation of each reform scenario at 2015 horizon on Romanian agriculture. This short analysis shows that, under the presented hypotheses, the net welfare effect, due to the price changes, for the selected products, is positive in both reform scenarios, yet greater in the case of the radical reform. Integrated in the large context of Romanian development, it seems that the influence of CAP reform upon agriculture and rural areas will be most likely a gradual one: an interpenetration between the two scenarios is foreseeable, starting with the moderate reform that will dominate the period around 2013, the reform measures acquiring a more radical character afterwards.CAP reform, Romania, welfare effects, Agricultural and Food Policy,
A Support Vector Machine Hydrometeor Classification Algorithm for Dual-Polarization Radar
No full textAn algorithm based on a support vector machine (SVM) is proposed for hydrometeor classification. The training phase is driven by the output of a fuzzy logic hydrometeor classification algorithm, i.e., the most popular approach for hydrometer classification algorithms used for ground-based weather radar. The performance of SVM is evaluated by resorting to a weather scenario, generated by a weather model; the corresponding radar measurements are obtained by simulation and by comparing results of SVM classification with those obtained by a fuzzy logic classifier. Results based on the weather model and simulations show a higher accuracy of the SVM classification. Objective comparison of the two classifiers applied to real radar data shows that SVM classification maps are spatially more homogenous (textural indices, energy, and homogeneity increases by 21% and 12% respectively) and do not present non-classified data. The improvements found by SVM classifier, even though it is applied pixel-by-pixel, can be attributed to its ability to learn from the entire hyperspace of radar measurements and to the accurate training. The reliability of results and higher computing performance make SVM attractive for some challenging tasks such as its implementation in Decision Support Systems for helping pilots to make optimal decisions about changes inthe flight route caused by unexpected adverse weather
Rich, Sturmian, and trapezoidal words
No full textIn this paper we explore various interconnections between rich words, Sturmian words, and trapezoidal words. Rich words, first introduced by the second and third authors together with J. Justin and S. Widmer, constitute a new class of finite and infinite words characterized by having the maximal number of palindromic factors. Every finite Sturmian word is rich, but not conversely. Trapezoidal words were first introduced by the first author in studying the behavior of the subword complexity of finite Sturmian words. Unfortunately this property does not characterize finite Sturmian words. In this note we show that the only trapezoidal palindromes are Sturmian. More generally we show that Sturmian palindromes can be characterized either in terms of their subword complexity (the trapezoidal property) or in terms of their palindromic complexity. We also obtain a similar characterization of rich palindromes in terms of a relation between palindromic complexity and subword complexity
Characterization Results for the Poset Based Representation of Topological Relations - I: Introduction and Models
No full text@article{DBLP:journals/informaticaSI/ForlizziN99,
author = {Luca Forlizzi and
Enrico Nardelli},
title = {Characterization Results for the Poset Based Representation
of Topological Relations - I: Introduction and Models.},
journal = {Informatica (Slovenia)},
volume = {23},
number = {2},
year = {1999},
bibsource = {DBLP, http://dblp.uni-trier.de}
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