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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigating the use of ray tracing for signal-level radar simulation in space monitoring applications: a comparison of radio propagation models

Martin, Mogamat Yaaseen 11 September 2023 (has links) (PDF)
This thesis presents the design and development of an accelerated signal-level radar simulator with an emphasis on space debris monitoring in the Low Earth Orbit. Space surveillance represents a major topic of concern to astronomers as the threat of space debris and orbital overpopulation looms – particularly due to the lack of effective mitigation techniques and the limitations of modern space-monitoring sensors. This work thus aimed to investigate and design possible tools that could be used for training, testing and research purposes, and thereby aid further study in the field. At present, there exist no three-dimensional, ray-traced, signal-level radar simulators available for public use. As such, this thesis proposes an open-source, ray-traced radar simulator that models the interactions between spaceborne targets and terrestrial radar systems. This utilises a ray-tracing algorithm to simulate the effects of debris size, shape, orientation, and material properties when computing radar signals in a typical simulation. The generated received signals, produced at the output of the simulator, were also verified against systems theory, and validated with an existing, well-established simulator. The developed software was designed to aid astronomers and researchers in space situational awareness applications through the simulation of radar designs for orbital surveillance experiments. Due to its open-source nature, it is also expected to be used in training and research environments involving the testing of space-monitoring systems under various simulation conditions. The software offers native support for measured Two-Line Element datasets and the Simplified General Perturbations #4 orbit propagation model, enabling the accurate modelling of targets and the dynamic orbital forces acting upon them. As a result, the software has aptly been named the Space Object Astrodynamics and Radar Simulator – or SOARS. SOARS was built upon the foundations of a general-purpose radar simulator known as the Flexible Extensible Radar Simulator – or FERS – which provided integrated radar models for propagation loss, antenna shapes, Doppler and phase shifts, Radar Cross Section modelling, pulse waveforms, high-accuracy clock mechanisms, and interpolation algorithms. While FERS lacked various features required for space-monitoring applications, many of its implementations were used in SOARS to minimise simulation limits and maximise signal rendering accuracy by supporting an arbitrary number of transmitters, receivers, and targets. The goal was thus to have the simulator limited only by the end-user's system, and to specialise the operation of the software towards space surveillance by integrating additional features – such as built-in models for environmental and system noise, multiscatter effects, and target modelling using meshes comprised of triangular primitives. After completing the software's development, the ray-traced simulator was compared against a more streamlined version of SOARS that made use of point-model approximations for quick-look simulations, and the trade-offs between both simulators (including software runtime, memory utilisation and simulation accuracy) were investigated and evaluated. This assessed the value of implementing ray tracing in a radar simulator operating primarily within space contexts and evaluated the results of both simulators using detection processing as a demonstrated application of the system. And while the use of ray tracing resulted in significant costs in speed and memory, the investigation found that the ray-traced simulator generated more reliable results relative to the point-model version – providing various advantages in test scenarios involving shadowing and multiscatter. The design of the SOARS software, as well as its point-model “baseline” alternative and the investigation into each simulator's advantages and disadvantages, are thus presented in this thesis. The developed programs were released as open-source tools under the GNU General Public Licence and are freely available for public use, modification, and distribution.
2

Modélisation et étude de performances dans les réseaux VANET / Modelling and performance study in VANET networks

Ait Ali, Kahina 16 November 2012 (has links)
Les réseaux véhiculaires sont des systèmes de communication basés sur un échange d'informations de véhicules à infrastructures fixes installées au bord des routes, on parle alors de mode V2I (Vehicle-to-Infrastructure), ou de véhicules à véhicules dit mode V2V (Vehicle-to-Vehicle) ou VANET (Vehicular Ad hoc Network). L'objectif est de fournir aux conducteurs et aux opérateurs de transport des informations sur le trafic routier permettant d'améliorer l'efficacité des systèmes de transport, la sécurité et le confort des usagers. Depuis leur apparition, les VANET ont connu un très grand essor, de nombreux standards, applications et mécanismes de routage ont été proposés pour répondre aux spécificités de cette nouvelle classe de réseaux. Les défis à relever pour leur conception découlent principalement de la forte mobilité des véhicules, de la diversité spatio-temporelle de la densité du trafic et de la propagation des ondes radio en environnement extérieur défavorable à l'établissement des communications sans fil. La difficulté, aussi bien économique que logistique, de la mise en œuvre réelle des réseaux véhiculaires fait de la simulation le moyen le plus largement utilisé pour la conception et l'évaluation des solutions proposées. Cependant la validité des résultats de simulation dépend fortement de la capacité des modèles utilisés à reproduire le plus fidèlement possible les situations réelles. Deux aspects sont essentiellement importants dans les VANET : la mobilité des véhicules et la propagation des ondes radio. Nous proposons dans cette thèse un nouveau modèle de mobilité et un nouveau modèle de propagation d’ondes radio pour réseaux de véhicules en environnement urbain et suburbain. Pour définir des schémas réalistes, ces deux modèles se basent sur des données statiques et dynamiques réelles sur les caractéristiques topographiques et socio-économiques de l'environnement. Ces données décrivent particulièrement la distribution spatio-temporelle des véhicules et les infrastructures présentes dans l'environnement. Trois cas d'études sont présentés dans la thèse pour la validation des modèles développés ; un environnement théorique, urbain ou suburbain, défini par l'utilisateur, notamment le cas Manhattan très utilisé, et deux environnements réels qui représentent des agglomérations de taille moyenne. Une autre contribution de cette thèse est l'étude de la connectivité radio et des performances des protocoles de routage dans les VANET. A partir de graphes dynamiques de connexions représentant la variation des liens radio entre véhicules en déplacement, nous avons analysé et déterminé les propriétés de la topologie des liaisons radio des réseaux véhiculaires. Pour étudier les protocoles de routage, nous avons utilisé le modèle de mobilité et le modèle de propagation radio que nous avons développés en association avec le simulateur de réseaux ns-2. Nous avons comparé les performances des protocoles de routage les plus répandus et déterminé les mécanismes de routage les plus adaptés aux réseaux véhiculaires. / Vehicular networks are communication systems based on information exchange either between vehicles and roadside fixed infrastructure, which is called V2I (Vehicle-to-Infrastructure) mode, or from vehicle to vehicle V2V (Vehicle-to-Vehicle) mode also known as VANET (Vehicular Ad hoc Network). The objective of these networks is to provide drivers and transport authorities the most timely information on road traffic in order to improve the efficiency of transportation systems, users safety and comfort.Since their appearance, the VANET have been greatly developed; many standards, applications and routing mechanisms have been proposed to address the specifics of this new class of networks. The challenges arise mainly from the high vehicles mobility, the spatiotemporal diversity of traffic density and, the radio waves propagation in external environment unfavorable to wireless communications establishment.The difficulty, both economic and logistical, of a real implementation of vehicular networks makes the simulation widely used to conceive and assess the proposed solutions. The validity of simulation results depends strongly on the ability of the models to reproduce as faithfully as possible the real situations. Two aspects are mainly important in the VANET: the simulation of vehicles mobility and radio wave propagation.We propose in this thesis a new mobility model and a new radio propagation model for vehicular networks in urban and suburban environment. To be realistic, these two models are based on real static and dynamic data describing the topographic and socioeconomic characteristics of the environment. These data concern particularly the spatiotemporal vehicles distribution and the description of the infrastructures present in the environment. Three case studies are presented in the thesis to validate the models, a theoretical user-defined urban or suburban environment (the Manhattan case very often used) and two real environments from mean size cities.Another contribution of this thesis is the study of radio connectivity and performance of routing protocols in the VANET. From dynamic graphs representing the variation of the radio links between vehicles in motion, we have analyzed and determined the topology properties of vehicular networks. To study routing protocols, we used the mobility model and the radio propagation model in association with the network simulator ns-2. We have compared the performance of the widespread routing protocols and determined the most adapted routing mechanisms to vehicular networks.

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