1,720,975 research outputs found
Hybridized-GNSS Approaches to Train Positioning: Challenges and Open Issues on Uncertainty
Get PDFIn recent years, the development of advanced systems and applications has propelled the adoption of autonomous railway traffic and train positioning, with several ongoing initiatives and experimental testbeds aimed at proving the suitability and reliability of the Global Navigation Satellite System signals and services, in this specific application domain. To satisfy the strict safety and accuracy requirements aimed at assuring the position solution's integrity, availability, accuracy and reliability, recent proposals suggest the hybridization of the Global Navigation Satellite System with other technologies. The integration with localization techniques that are expected to be available with the upcoming fifth generation mobile communication networks is among the most promising approaches. In this work, different approaches to the design of hybrid positioning solutions for the railway sector are examined, under the perspective of the uncertainty evaluation of the attained results and performance. In fact, the way the uncertainty associated to the positioning measurements performed by different studies is reported is often not consistent with the Guide to the Expression of Uncertainty in Measurement, and this makes it very difficult to fairly compare the different approaches in order to identify the best emerging solution. Under this perspective, the review provided by this work highlights a number of open issues that should drive future research activities in this field
GNSS Integrity Monitoring for Rail Applications: 2-tiers method
No full textThe paper presents an innovative GNSS fault detection and exclusion approach for the adoption of satellite localization in the rail sector. Current global integrity monitoring systems cannot guarantee the safety level needed for such applications as train control where Tolerable Hazard Rate in the order of 10 is required. A new method, named 2-tiers, enabling to integrate local augmentation systems and global augmentation infrastructures, is presented. It is based on the comparison of single differences residuals among satellites for detecting signal in space faults and double difference residuals among local augmentation stations and SBAS RIMS for detecting reference stations faults. GPS SIS faults described in literature and real GNSS raw data recorded on a train are taken into account. The present work reports the performance analysis for the 2-tiers approach carried out during relevant European projects. A Test-Bed architecture has been developed through the implementation of the algorithm in real-time on a local augmentation operational centre. Relevant performances have been tested on a rail track for validating the algorithm in real operative conditions. Significant results of the analysis are reported for SIS integrity assessment only
Ionospheric incremental delay models in railway applications
No full textThe paper focuses on the introduction of the GNSS technology into the frame of the train control system. The goal of this work is to analyse and compare the existing ionospheric incremental delay models influence on accuracy of On Board Unit (OBU) position to verify the achievable performance by adopting them during the estimation procedure. The performance results will be shown, based on a campaign test acquired on a ring-shaped highway (named Grande Raccordo Anulare (GRA)) around Rome (Italy) to simulate movement of a train on a generic track
Spoofing Impact on GNSS Integrity in the Transport Context: A Tool for the Performance Analysis
No full textThe present work shows the results of a performance analysis for evaluating the impact of spoofing on GNSS Integrity for transport applications. Spoofing represents a potential risk to be managed for GNSS safety-related land mobile applications. To this aim a Virtual Test Bed has been generated. A rover receiver has been developed through an SDR, and relevant spoofed signal injected through a hardware simulator. A performance analysis software simulator performed relevant integrity study. Stanford plots have been generated for analyzing integrity performance to guarantee a THR=10-9/h in DGNSS mode
Performance evaluation in terms of accuracy positioning of local augmentation and integrity monitoring network for railway sector
No full textThis paper proposes a local augmentation and integrity monitoring network for railway and shows the obtained performances in terms of accuracy positioning in case of satellite faults. The simulations results show that the system can detect and discard tha faulty satellite, still mantaining the accuracy on positioning accetable. The work is inserted in the scenario of introduction and application of space technologies based on the ERTMS (European Railways Train Management System) architecture. It foresees to include the EGNOS-Galileo infrastructures in the train control system, with the aim at improving performance, enhancing safety and reducing the investments on the railways circuitry and its maintenance. © 2014 IEEE
Wireless technologies for future multi-gigabit communications beyond 60 GHz: design issues and performance analysis for terrestrial and satellite applications
Get PDFOggigiorno la richiesta di comunicazioni wireless ad alto data rate cresce proporzionalmente alle velocità di trasferimento dati raggiungibili mediante l’uso della fibra ottica. Infatti, la tendenza ultima in materia di ricerca è quello di sviluppare sistemi che consentano a utenti mobili velocità di connessione almeno confrontabili con quello della Ethernet Wired. Lo standard GbE è ormai consolidato, mentre quello 10 GbE è disponibile dal 2002. Mentre la tecnologia in fibra ottica è in grado di fornire data rate dell’ordine di alcuni multi-gigabit/s, i costi ed i tempi per la sua messa in opera sono ancora proibitivi per alcune applicazioni. Ponti wireless troverebbero impiego nella copertura dei buchi nella rete in fibra con costi contenuti e senza azioni complesse di scavo. In questo scenario, le comunicazioni wireless ai multigigabit consentiranno di sostituire il segmento in fibra nei futuri sistemi di terza e quarta generazione, nei sistemi di antenna distribuiti, nelle applicazioni commerciali come la trasmissione di video ad alta definizione (HDTV). Le singole abitazioni così come gli interi complessi residenziali nei prossimi decenni potranno usufruire, grazie alle comunicazioni wireless ai multi gigabit, di nuovi servizi ed applicazioni. La necessità di così alto contenuto informativo dunque emergera’ sia in scenari a corto raggio che medio-lungo.
Dove una così elevata larghezza di banda necessaria per realizzare comunicazioni wireless ai multi-gigabit e’ presente senza problematiche di interferenza?
L’attenzione cade sulle EHF dove sono disponibili grandi porzioni di banda. Recentemente, si e’ mostrato grande interesse per lo sviluppo di sistemi operanti a 60 GHz per applicazioni sia indoor che outdoor, essendo in diversi paesi non licenziata. Comunque, a causa dell’elevata attenuazione dovuta al picco di assorbimento dell’ossigeno a queste frequenze, tali sistemi non sono indicati per lunghi collegamenti. Inoltre, le FCC hanno stabilito che le frequenze nello spettro tra i 70-95 GHz (quindi lontane dallo bande in cui c’è il picco massimo di assorbimento ossigeno) possano essere impiegate per uso semi-licenziato al fine di realizzare collegamenti “ultimo miglio”. D’altra parte, sopra i 60 GHz, sia su breve che corto raggio, la letteratura manca ancora di conoscenze dettagliate sulle tecniche di trasmissione, modulazione, equalizzazione piu’ opportune a queste frequenze. Il seguente lavoro di tesi ha mirato quindi ad investigare le potenzialita’ di interface radio innovative ed avanzate, come quelle basate su tecniche di trasmissione IR-UWB, per le future generazioni delle comunicazioni wireless oltre i 60 GHz per applicazioni ai Multi-gigabit/s. In particolare, questo lavoro mostra come un sistema di comunicazione del tipo IR-UWB sia sensibile alle non linearita’ circuitali tipiche a queste frequenze (Phase Noise, Timing Jitter, LNA, HPA) e confronta le prestazioni con altri schemi di trasmissione e ricezione piu’ tradizionali utilizzabili oltre i 60 GHz (in particolar modo FSK). L’obiettivo principale del lavoro è stato quello di capire vantaggi e svantaggi di un sistema di trasmissione “impulsato” nello scenario considerato rispetto, considerando appunto tutte le peculiarità propagative e tecnologiche nell’uso delle EHF.
L’utilizzo di frequenze così alte rappresenta la soluzione più adeguata per realizzare una infrastruttura cooperative per un’informazione globale al fine di garantire la cosiddetta “Connettività ai Gigabit” sfruttando collegamenti aerospaziali. Cio’ e’ mirato a fare in modo che un tale segmento radio costituisca una sorta di potenziale “dorsale in aria” per una connettività wireless globale.
Quindi, l’uso delle bande di frequenza oltre le Q/V sarà la condizione necessaria per sviluppare una rete multi-purpose, come integrazione dei sistemi terrestri e spaziali, al fine di supportare le emergenti richieste di servizio ad alto contenuto informativo.
La Banda W (75-110 GHz, rispettivamente 4 -2.7 mm) potrebbe rappresentare la risposta a queste necessità in virtù di una larghezza di banda elevata, corte lunghezze d’onda, ridotte dimensioni delle antenne, consentendo di proporre diversi innovativi servizi che necessitano di trasferimenti dati ad alta velocità.
Attualmente, purtroppo, le prestazioni di una qualunque soluzione per trasporto dati a tali frequenze attraverso la Troposfera non sono ancora note, dal momento che nessuna missione scientifica e/o per telecomunicazioni è stata realizzata, né su base sperimentale né operativamente. Quindi, missioni in banda W devono essere studiate ai fini di realizzare una prima valutazione empirica degli effetti della Troposfera sul canale radio. Quindi, l’ultima parte del mio lavoro di tesi è stato focalizzato sulla analisi e valutazione di prestazione di future missioni per l’uso della banda W anche per le comunicazioni satellitari che prevedano una linea completa di P/L operanti a tali frequenze. Lo studio e la valutazione di prestazione di missioni miranti a fornire una prima valutazione empirica degli effetti della Troposfera sul canale radio in banda W rappresenta il primo passo utile per la realizzazione di un “Sistema di Sistemi” che sia in grado di soddisfare le richieste di trasmissioni dati ad alto contenuto informativo per un grande numero di utenti finali e servizi orientati ad applicazioni specifiche.Demand for very high-speed wireless communications is proportionally growing with respect to the increasing data rates reachable by optical fibers. In fact, the emerging research trend in computer networks is to cut more and more cables and to provide mobile and nomadic users with a data rate at least comparable with that one of wired Ethernet. GbE standard is now widespread and 10 GbE standard has been available since 2002.
While established and well-known fiber-optic data-transfer devices can provide multigigabit per second data rates, infrastructure costs and deployment time can be too expensive for some applications. Wireless links can be used to bridge the gaps in the fiber network and they can be deployed very rapidly, without the need for costly and complex trenching actions. Multigigabit wireless applications will include fiber segment replacement in future 3G and 4G backhauls, in distributed antenna systems, in enterprise connectivity, and in consumer-level applications, such as HDTV. Future home and building environments are a domain where, in the coming decade, large quantitative and qualitative changes can be expected in services and applications, that ultimately will benefit from wireless multigigabit/s communication. Therefore, the need for such high data rates arises both in short-range scenarios and in medium-long range scenarios.
Where a very huge bandwidth for multigigabit wireless communications can be made available as free spectrum without interference issues? The unique possibility is to look at EHF. Recently, there has been a lot of interest in the development of 60 GHz systems for the indoor and outdoor applications, because this bandwidth has been allocated in many countries as free spectrum. However, because of higher propagation loss due to oxygen absorption at this band, it is not suitable for very long links. Further, the FCC has made available 13 GHz of spectrum in the 70-95 GHz (away from the oxygen absorption band, in order to facilitate longer range communication) for semi-unlicensed use for directional point-to-point “last mile” links. However, above 60 GHz, both for long and short range, there is a lack of discussion on modulation, equalization, and algorithm design at physical layer. This work mainly aims at investigating the possibility to use innovative and advanced radio interfaces, as one based on IR UWB transmission technique, to realise multigigabit/s communications beyond 60 GHz.
In particular, this work shows how an IR UWB communication system is sensitive to typical H/W not idealities beyond 60 GHz (Phase Noise, Timing Jitter, LNA and HPA distortions) and compares its performance with the ones of a more classical continuous wave communications system based on FSK modulation.
The exploitation of such higher frequencies represents the most suitable solution to develop a cooperative global information infrastructure in order to guarantee the so-called “Gigabit Connectivity” through aerospace links making such a radio segment a potential “backbone on the air” for global wireless connectivity. Therefore, the use of “beyond Q/V bands” will be the necessary condition to develop a multipurpose network, as integration of terrestrial and space systems, in order to support forthcoming high-data-rate services demands. W band (75-110 GHz, respectively 4 -2.7 mm) could represent the answer to these needs due to the high bandwidth availability, short wavelength, reduced interference, small antenna size, allowing to propose many innovative services that need high-volume transfers. Currently, however, the performance behaviour of any solution for data transportation over W band frequencies across the Troposphere is still unknown, since no scientific and/or telecommunication mission has been realised, either on an experimental basis or in an operating mode. Therefore, missions in W band have to be studied in order to perform a first empirical evaluation of the Troposphere effects on the radio channel. Consequently, the last part of this work has been focused on the analysis and performance evaluation of future missions for the exploitation of W band too for satellite communications aiming at designing a full line of P/Ls operating in such a frequency range. The design and performance analysis of missions to perform a first empirical evaluation of the Troposphere effects on the W band radio channel represent the preliminary useful step for realising a “System of Systems” which is able to meet the high-quality data transmission requirements for a large number of end-users and data-oriented services
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
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