1,720,952 research outputs found
Performance improvement of a MLS compatible DGPS-datalink
No full textThe datalink, a part of the Multimode Integrated Approach System (MIAS) which transmits the Differential GPS message, is currently implemented by using the Auxiliary Datawords type C, provided by the Microwave Landing System (MLS). The performance of the datalink is currently dependent on the characteristics of the ADW-C words used for transmitting the DGPS message. When receiving the message, it is important to know whether it is correctly received and if not, whether it is possible to correct the errors. Although the ADW-C word provides for some error detection, the probability of undetected error is not low enough in order for it to meet integrity requirements for a CAT III approach and landing. Furthermore, the correction capability could also be improved. Therefore, this report discusses the characteristics of the current datalink. Addressing the lack of integrity when using ADW-C words, the implementation of a Cyclic Redundancy Check (CRC) is discussed. This extra check improves the integrity near demands that are set for this quantity by ICAO…Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
The implementation of an object-oriented C-band datalink ray tracing model
No full textThis thesis report gives a brief introduction to object-oriented modelling, and the development of an object-oriented model of a C-band datalink, as well as the implementation of this model in software. This work is done in the context of the Multi-Mode Integrated Approach System (MIAS) research, to develop a tool for the estimation of the propagation effects on the datalink signals.Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
Integrated navigation system eurofix: Vision, concept, design, implementation & test
No full textElectrical Engineering, Mathematics and Computer Scienc
Eurofix: phase stability of Loran-C on a microscopic level
No full textEuro fix is an integrated navigation system proposed by Delft University of Technology. It is based on the combination of two radionavigation systems: A satellite-oriented navigation system (GNSS, for example the Global Positioning System -GPS- or Glonass) and the Loran-C system. The Loran- C system can be used both as a backup navigation system and as a datalink to broadcast DGNSS and integrity information. In areas where the GNSS satellite signals are lost, for example in an urban environment, the Eurofix user can still calculate the position with Loran-C. This paper describes the phase stability of Loran-C, focusing on the influences of clutter. It further concentrates on the difference in phase development between the electric and magnetic field and on the stability of the time difference of the Loran-C signals. On a microscopic level measurement runs have been taken at various scenarios to investigate the influence of urban conditions. By correcting the phase of the signal for the displacements, the results then give the phase differences of the signals over the runs. It is shown that the phase of the Loran-C signal can be disturbed by several tens of meters when the signals are received in urban environments. Also the disturbance of the phase is less for a magnetic field antenna than for an electric field antenna. The measurements further show that the phases of two transmitters seem to be influenced in the same manner when the user is on the base-line of those two transmitters. Finally, the paper shows that the time differences of the Loran-C signals vary in such a magnitude that the accuracy of Loran-C positioning degrades significantly under urban conditions.Electrical Engineering, Mathematics and Computer ScienceTelecommunicatie- en Verkeersbegeleidingssysteme
Improving the DGNSS performance of Eurofix Using WLS algorithms, focusing on Temporal decorrelation effects
No full textEurofix is an integrated navigation system, which combines Differential GNSS and Loran-C. The Loran-C system is used to transmit messages which contain differential corrections for GNSS by additional modulation of the transmitted signals. It has been shown that reliable data transmission using Loran-C stations up to 1000 km distance is feasible. The differential corrections are generated by a DGNSS reference station located at the Loran-C transmitter site, providing DGNSS service to all users within the datalink range. Unfortunately, different time varying conditions at the DGNSS reference station and GNSS user position, introduce positioning errors. This paper mainly focuses on the temporal aspects of the errors. In the current implementation of Eurofix the calculation ofposition is solved by means of an ordinary least squares algorithm using at least 5 measured satellite range measurements. When using Weighted Least Squares (WLS), extra available information about the error-sources of GNSS and DGNSS can be taken into account. This way higher positioning accuracies can be obtained. The weight factors of WLS are related to the measurements-error-properties caused by the earth 's atmosphere and the data latency of the Eurofix communication link. Another option for positioning could be to use a Kalman filter. However it will be shown that the conditions for this filter are currently not met by the Eurofix measurements. Finally the theory is put into practice and some interesting real-life test results are presented, showing that the already high accuracy can still be improved.Electrical Engineering, Mathematics and Computer ScienceTelecommunicatie- en Verkeersbegeleidingssysteme
Eurofix: Test Results of a Cost-Effective DGNSS Augmentation System
No full textEurofix is an integrated navigation system, which combines Differential GNSS and Loran-C. The Loran-C system is used to provide differential corrections for the GNSS pseudo-range measurements and integrity information by additionally modulating the transmitted signals. This modulation, however, is not allowed to degrade normal Loran-C operations. As data transmission is hindered by the aggressive Loran-C signal environment, special modulation patterns and Forward Error Correcting codes are designed to fulfil the requirements. Compared to other DGNSS services, Eurofix has a number of advantages: It covers a large area, its implementation in an already existing infrastructure is basically low-cost, it offers enhanced datalink availability in urban and mountainous environment, it has wide-area capabilities and, finally, it provides a free backup navigation system in case either Loran-C or GPS fails. The paper describes the Eurofix system, focusing on the Loran-C data channel. A modified RTCM type-9 message format is used with special Forward Error Correction. At Delft University a real-life test set-up has been built to evaluate the Eurofix performance for different scenarios. The results on datalink and DGNSS performance are presented. It is shown that metre-level DGNSS performance is achievable with low bit rate data channels, using Loran-C stations at up to iooo km distance.Delft University of Technolog
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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