Multipath and interference errors reduction in gps using antenna arrays

The Global Positioning System (GPS) is a worldwide satellite based positioning system that provides any user with tridimensional position, speed and time information. The measured pseudorange is affected by the multipath propagation, which probably is the major source of errors for high precision systems. After a presentation of the GPS and the basic techniques employed to perform pseudorange measurements, the influence of the multipath components on the pseudorange measurement is explained. Like every system the GPS is also exposed to the errors that can be caused by the interferences, and a lot of civil applications need robust receivers to interferences for reasons of safety. In this paper some signal array processing techniques for reducing the code measurement errors due to the multipath propagation and the interferences are presented. Firstly, a non-adaptive beamforming is used. Secondly, a variant of the MUSIC and the maximum likelihood estimator can be used to estimate the DOA of the reflections and the interferences, and then a weight vector that removes these signals is calculated. In the third place, a beamforming with temporal reference is presented; the reference is not the GPS signal itself, but the output of a matched filter to the code. An interesting feature of the proposed techniques is that they can be applied to an array of arbitrary geometry.Peer ReviewedPostprint (published version

Code-timing synchronization in DS-CDMA systems using space-time diversity

The synchronization of a desired user transmitting a known training sequence in a direct-sequence (DS) asynchronous code-division multiple-access (CDMA) sys-tem is addressed. It is assumed that the receiver consists of an arbitrary antenna array and works in a near-far, frequency-nonselective, slowly fading channel. The estimator that we propose is derived by applying the maximum likelihood (ML) principle to a signal model in which the contribution of all the interfering compo-nents (e.g., multiple-access interference, external interference and noise) is modeled as a Gaussian term with an unknown and arbitrary space-time correlation matrix. The main contribution of this paper is the fact that the estimator makes eÆcient use of the structure of the signals in both the space and time domains. Its perfor-mance is compared with the Cramer-Rao Bound, and with the performance of other methods proposed recently that also employ an antenna array but only exploit the structure of the signals in one of the two domains, while using the other simply as a means of path diversity. It is shown that the use of the temporal and spatial structures is necessary to achieve synchronization in heavily loaded systems or in the presence of directional external interference.Peer ReviewedPostprint (published version

Maximum likelihood time-of-arrival estimation using antenna arrays: Application to global navigation satellite systems

The problem of estimating the time-of-arrival (TOA) of a known signal in the presence of interferences and multipath propagation is addressed. This problem, is essential in high precision receivers of the Global Navigation Satellite Systems. This paper presents the maximum likelihood TOA estimator when an antenna array is used in the receiver. The desired signal impinges the array with a known direction-of-arrival (DOA) vector, which allows to model all the undesired signal as unknown and arbitrary spatially correlated noise. This simplified model makes only the desired parameters remain in the formulation explicitly, then avoiding complex maximization schemes needed by other models. The fact that estimator is formulated in the frequency domain permits the introduction of the temporal correlation of the noise. Simulation results illustrate the satisfactory performance of the estimator.Peer ReviewedPostprint (published version

Los presidentes del Concilio de Nicea de 325

Esta nota se ocupa de las actitudes mantenidas por el emperador Constantino I el Grande y los obispos Alejandro de Alejandría, Osio de Córdoba, Eustacio de Antioquia y Macario de Jerusalén frente al Arrianismo inicial. También se tratan los problemas concernientes a la presidencia del concilio de Nicea en el año 325 d.C.This note deals with the attitudes maintained by the emperor Constantine I the Great and Bishops Alexander of Alexandria, Ossius of Cordoba, Eustathius of Antioch and Macarius of Jerusalem in front of Early Arianism. Also the note deals with the problems concerning the Presidency of the Council of Nicaea in year 325 A.D

Las consagraciones de las basílicas romanas de San Cosme y Damián, Santa maría "ad Martyres" y San Andriano "in tribus fatis"

Este artículo estudia las consagraciones de las Basílicas romanas de San Cosme y Damián, Santa María ad martyres y San Adriano in Tribus Fatis en relación con las políticas ostrogoda y bizantina ante el Papado. (A

Strategic Tax Competition with a Mobile Population

This paper analyzes a model of strategic tax competition with mobile capital and mobile identical consumers. The results of the model are compared to the traditional strategic tax competition model with immobile population. In addition to the fiscal and pecuniary externalities present in the standard model, a new effect shows up in the mobility model to affect provision of the public good. As with the pecuniary externality, this new effect depends on whether the jurisdictions are net exporters or net importers of capital. Thus, in a symmetric set up, the mobility effect along with the pecuniary externality disappear, yielding unambiguous underprovision of the public good. While in the asymmetric case both models have the same qualitative results, the mobility model strengthens the effects of the pecuniary externality. The above results are obtained by comparing the form of the first-order conditions between the mobility and immobility cases. The remaining question is whether or not the equilibrium levels of the public goods conform to the predicted tendencies. This question is answered with an example. The results of this exercise show that when the jurisdiction is a net exporter of capital, the level of the public good is lower in the mobility case than in the immobility case. However, if the jurisdiction is a net importer of capital, the public good level is sometimes higher and sometimes lower in the mobility case, contrary to predictions.Facultad de Ciencias Económica

Strategic Tax Competition with a Mobile Population

This paper analyzes a model of strategic tax competition with mobile capital and mobile identical consumers. The results of the model are compared to the traditional strategic tax competition model with immobile population. In addition to the fiscal and pecuniary externalities present in the standard model, a new effect shows up in the mobility model to affect provision of the public good. As with the pecuniary externality, this new effect depends on whether the jurisdictions are net exporters or net importers of capital. Thus, in a symmetric set up, the mobility effect along with the pecuniary externality disappear, yielding unambiguous underprovision of the public good. While in the asymmetric case both models have the same qualitative results, the mobility model strengthens the effects of the pecuniary externality. The above results are obtained by comparing the form of the first-order conditions between the mobility and immobility cases. The remaining question is whether or not the equilibrium levels of the public goods conform to the predicted tendencies. This question is answered with an example. The results of this exercise show that when the jurisdiction is a net exporter of capital, the level of the public good is lower in the mobility case than in the immobility case. However, if the jurisdiction is a net importer of capital, the public good level is sometimes higher and sometimes lower in the mobility case, contrary to predictions.Facultad de Ciencias Económica

The quest for dark matter in dwarf spheroidal galaxies with the Cherenkov Telescope Array

Dwarf spheroidal galaxies are among the best environments that can be studied with Cherenkov telescopes for indirect searches of $\gamma$-ray signals coming from dark matter self-interaction (annihilation or decay), due to their proximity and negligible background emission. We present new determinations of the dark-matter amount - i.e. the astrophysical factors $J$ and $D$ - in dwarf-galaxy halos obtained through the MCMC Jeans analysis of their brightness and kinematic data. Such factors are of great importance to test the performances of the next-generation $\gamma$-ray instruments such as the Cherenkov Telescope Array in detecting dark-matter signals from astronomical environments, or constraining the limits to dark-matter physics parameters (particle mass and lifetime, annihilation cross section).Comment: 4 pages, 2 figures, 1 table, proceedings of the "RICAP-18 - 7th Roma International Conference on Astroparticle Physics" held on 2018 Sep 04-07 at Universit\`a di "Roma Tre", Via V. Volterra 62, I-00182 Roma, Italy (to appear on EPJ Web of Conferences