1,720,963 research outputs found
A proposed fault detection and exclusion method applied to multi-GNSS single-frequency PPP
No full textIn the last few years, Precise Point Positioning (PPP) has become widespread as a standalone positioning technique. Unlike classical GNSS point positioning, which uses the pseudorange observables from four or more visible satellites and the broadcast ephemeris to obtain the user instantaneous position, PPP takes the advantage of the more precise carrier phase measurements, attempting to account for all the GNSS errors and biases. PPP is able to provide accuracy level comparable to differential positioning. In particular, the single-frequency (SF) PPP technique is attracting great interest, since SF GNSS devices are widely used for most positioning and navigation applications. For this aim, the paper proposes a SF-PPP approach based on the use of code and single-frequency ionosphere-free linear observables combination, collected from GPS and Galileo systems. In addition, an integrity monitoring algorithm is modified to be applied to SF-PPP for the detection, isolation and the removal of faulty measurement sources. The proposed strategy is tested using real and simulated data gathered in static mode. Results demonstrate the effectiveness of the proposed integrity monitoring algorithm, applied to SF-PPP
Fuzzy logic applied to GNSS
No full textLimiting the weight of bad signals can recover the accuracy of the GNSS solution in signal-degraded scenarios, where multipath reflections and obstructions can easily generate multiple blunders. The fuzzy integration of the available information related to the quality of the received signals is exploited in this paper to derive an effective weighting schema in a Weighted Least Square estimation process. To validate the proposed schema, its performance in the position domain is compared to the most common weighting strategies proposed in the literature, based on GPS data collected through two different High Sensitivity GNSS receivers placed in urban canyons and processed in Single Point Positioning using pseudorange measurements
NeQuick Galileo version model: Assessment of a proposed version in operational scenario
No full textThe ionosphere is one of the main error sources for single-frequency Global Navigation Satellite System (GNSS) measurements in open-sky scenario. Most widespread GNSS devices are single frequency stand-alone receivers and they can use different Ionospheric Correction Algorithms (ICA) in order to reduce the ionospheric error. In this work two ICA models are considered, specifically Klobuchar and NeQuick-G models. These algorithms are driven by parameters broadcast within GPS and Galileo navigation messages respectively. Hence no additional infrastructure is needed to reduce the ionospheric effects. The main goal of the paper is to analyze the performance of a modified approach for NeQuick-G (defined NeQuick VP) by comparing its performance, in position domain, with respect to the standard NeQuick-G algorithm and to Klobuchar one. NeQuick VP is a methodology proposed to reduce the complexity characterizing NeQuick-G model. The performance is evaluated using real data collected by an open-sky station; the results obtained are analyzed using Root Mean Square (RMS), mean and maximum errors as Key Performance Indicators (KPIs) for both horizontal and vertical components
Robust Estimation Methods Applied to GPS in Harsh Environments
No full textSatellite navigation is very widespread in civil society; many devices and services exploit this technology and several systems are in use or in development phase. GNSS receiver, embedded in devices used in daily life (smartphones, cars and so on), works in several conditions and operational scenarios. Ensuring good positioning accuracy is challenging, especially in environment where receiver measurements are affected by gross errors, such as urban canyons. In this paper, the benefit of robust estimators in case of multiple simultaneous blunders is investigated; several robust estimators were implemented and their performances are compared with classical techniques used in GNSS context (WLS, RAIM) using real data. Effectiveness of these methods raised from tests conducted in static and kinematic mode
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Reliability testing for multiple GNSS measurement outlier detection
No full textDue to a rapid development of several Global Navigation Satellite Systems (GNSS), multiple constellations are available to enhance navigation performance and safety. With the growing number of satellite constellations, the task of the GNSS navigation is to deal with the differences among systems but, on the other hand, more great levels of integrity and satellite visibility can be expected. GNSS navigation applications have difficulties in signal degraded scenarios where the GNSS solution can be degraded by errors such as multipath and signals being obscured. RAIM (Receiver Autonomous Integrity Monitoring) is a method necessary for assessing integrity performance levels mainly in safety-critical applications. Classical RAIM techniques are based on the assumption model of a single outlier in the measurements, but with a future of higher satellite availability and for navigation conducted in urban canyon scenarios, the single outlier assumption is unrealistic. Therefore, reliability monitoring techniques need to be modified to be suitable for use cases with high signal degradation levels. The FDE (Fault Detection and Exclusion) schemes analysed in this research for reliability monitoring are the Observation Subset Testing and a modified approach based on a w-test (called in this paper Multiple Faults De-weighting-MFD). In order to improve their performance a novel Channel Quality Index (CQI) parameter was used to describe the measurement confidence and quality. To validate the proposed approaches, tests have been performed using simulated data with GPS, Galileo and BeiDou signals in a multipath environment
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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