96 research outputs found

    Lunar Relay Satellite Network for Space Exploration: Architecture, Technologies and Challenges

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    NASA is planning a series of short and long duration human and robotic missions to explore the Moon and then Mars. A key objective of these missions is to grow, through a series of launches, a system of systems infrastructure with the capability for safe and sustainable autonomous operations at minimum cost while maximizing the exploration capabilities and science return. An incremental implementation process will enable a buildup of the communication, navigation, networking, computing, and informatics architectures to support human exploration missions in the vicinities and on the surfaces of the Moon and Mars. These architectures will support all space and surface nodes, including other orbiters, lander vehicles, humans in spacesuits, robots, rovers, human habitats, and pressurized vehicles. This paper describes the integration of an innovative MAC and networking technology with an equally innovative position-dependent, data routing, network technology. The MAC technology provides the relay spacecraft with the capability to autonomously discover neighbor spacecraft and surface nodes, establish variable-rate links and communicate simultaneously with multiple in-space and surface clients at varying and rapidly changing distances while making optimum use of the available power. The networking technology uses attitude sensors, a time synchronization protocol and occasional orbit-corrections to maintain awareness of its instantaneous position and attitude in space as well as the orbital or surface location of its communication clients. A position-dependent data routing capability is used in the communication relay satellites to handle the movement of data among any of multiple clients (including Earth) that may be simultaneously in view; and if not in view, the relay will temporarily store the data from a client source and download it when the destination client comes into view. The integration of the MAC and data routing networking technologies would enable a relay satellite system to provide end-to-end communication services for robotic and human missions in the vicinity, or on the surface of the Moon with a minimum of Earth-based operational support

    Identification of Technologies for Provision of Future Aeronautical Communications

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    This report describes the process, findings, and recommendations of the second of three phases of the Future Communications Study (FCS) technology investigation conducted by NASA Glenn Research Center and ITT Advanced Engineering & Sciences Division for the Federal Aviation Administration (FAA). The FCS is a collaborative research effort between the FAA and Eurocontrol to address frequency congestion and spectrum depletion for safety critical airground communications. The goal of the technology investigation is to identify technologies that can support the longterm aeronautical mobile communication operating concept. A derived set of evaluation criteria traceable to the operating concept document is presented. An adaptation of the analytical hierarchy process is described and recommended for selecting candidates for detailed evaluation. Evaluations of a subset of technologies brought forward from the prescreening process are provided. Five of those are identified as candidates with the highest potential for continental airspace solutions in L-band (P-34, W-CDMA, LDL, B-VHF, and E-TDMA). Additional technologies are identified as best performers in the unique environments of remote/oceanic airspace in the satellite bands (Inmarsat SBB and a custom satellite solution) and the airport flight domain in C-band (802.16e). Details of the evaluation criteria, channel models, and the technology evaluations are provided in appendixes

    Adaptation of the IEEE 802.11 protocol for inter-satellite links in LEO satellite networks

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    Knowledge of the coefficient of thermal expansion (CTE) of a ceramic material is important in many application areas. Whilst the CTE can be measured, it would be useful to be able to predict the expansion behaviour of multiphase materials.. There are several models for the CTE, however, most require a knowledge of the elastic properties of the constituent phases and do not take account ofthe microstructural features of the material. If the CTE could be predicted on the basis of microstructural information, this would then lead to the ability to engineer the microstructure of multiphase ceramic materials to produce acceptable thermal expansion behaviour. To investigate this possibility, magnesia-magnesium aluminate sp~el (MMAS) composites, consisting of a magnesia matrix and magnesium aluminate s~ne'l (MAS) particles, were studied. Having determined a procedure to produce MAS fr alumina and magnesia, via solid state sintering, magnesia-rich compositions wit ~ various magnesia contents were prepared to make the MMAS composites. Further, the l\.1MAS composites prepared from different powders (i.e. from an alumina-magnesia mixture ahd from a magnesia-spinel powder) were compared. Com starch was added into the powder mixtures before sintering to make porous microstructures. Microstructural development and thermal expansion behaviour ofthe MMAS composites were investigated. Microstructures of the MAS and the MMAS composites as well as their porous bodies were quaritified from backscattered electron micrographs in terms of the connectivity of solids i.e. solid contiguity by means of linear intercept counting. Solid contiguity decreased with increasing pore content and varied with pore size, pore shape and pore distribution whereas the phase contiguity depended strongly on the chemical composition and was less influenced by porosity. ' The thermal expansion behaviour of the MAS and the MMAS composites between 100 and 1000 °C was determined experimentally. Variation in the CTE ofthe MAS relates to the degree of spinel formation while the thermal expansion of the MMAS composites depends strongly on phase content. However, the MMAS composites with similar phase compositions but made from different manufacturing processes showed differences in microstructural features and thermal expansion behaviour. Predictions of the CTE values for composites based on a simple rule-of-mixtures (ROM) using volume fraction were compared with the measured data. A conventional ROM accurately predicted the effective CTE of a range of dense alumina-silicon carbide particulate composites but was not very accurate for porous multiphase structures. It provided an upper bound prediction as all experimental values were lower. Hence, the conventional ROM was modified to take account of quantitative microstructural parameters obtained from solid contiguity. The modified ROM predicted lower values and gave a good agreement with the experimental data. Thus, it has been shown that quantitative microstructural information can be used to predict the CTE of multiphase ceramic materials with complex microstructures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

    Architectural Model for Evaluating Space Communication Networks

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    [ANGLÈS] The space exploration endeavor started in 1957 with the launch and operation of the first manmade satellite, the URSS Sputnik 1. Since then, multiple space programs have been developed, pushing the limits of technology and science but foremost unveiling the mysteries of the universe. In all these cases, the need for flexible and reliable communication systems has been primordial, allowing the return of collected science data and, when necessary, ensuring the well-being and safety of astronauts. To that end, multiple space communication networks have been globally deployed, be it through geographically distributed ground assets or through space relay satellites. Until now most of these systems have relied upon mature technology standards that have been adapted to the specific needs of particular missions and customers. Nevertheless, current trends in the space programs suggest that a shift of paradigm is needed: an Internet-like space network would increase the capacity and reliability of an interplanetary network while dramatically reducing its overall costs. In this context, the System Architecting Paradigm can be a good starting point. Through its formal decomposition of the system, it can help determine the architecturally distinguishing decisions and identify potential areas of commonality and cost reduction. This thesis presents a general framework to evaluate space communication relay systems for the near Earth domain. It indicates the sources of complexity in the modeling process, and discusses the validity and appropriateness of past approaches to the problem. In particular, it proposes a discussion of current models vis-Ă -vis the System Architecting Paradigm and how they fit into tradespace exploration studies. Next, the thesis introduces a computational performance model for the analysis and fast simulation of space relay satellite systems. The tool takes advantage of a specifically built-in rule-based expert system for storing the constitutive elements of the architecture and perform logical interactions between them. Analogously, it uses numerical models to assess the network topology over a given timeframe, perform physical layer computations and calculate plausible schedules for the overall system. In particular, it presents a newly developed heuristic scheduler that guarantees prioritization of specific missions and services while ensuring manageable computational times.[CASTELLÀ] El inicio de la carrera espacial se iniciĂł en 1957 con el lanzamiento y operaciĂłn del primer satĂ©lite artificial, el Sputnik 1 de la URSS. Desde entonces se han desarrollado mĂșltiples programas espaciales que han llevado al lĂ­mite tanto la tecnologĂ­a como la ciencia y han permitido desvelar los misterios del universo. En todos estos casos, la necesidad de sistemas de comunicaciĂłn flexibles y fiables ha sido primordial con el fin de asegurar el retorno de los datos cientĂ­ficos recopilados y, en ciertos casos, garantizar la seguridad de los astronautas. Como consecuencia, mĂșltiples redes de comunicaciones espaciales han sido desplegadas, ya sea a travĂ©s de antenas globalmente distribuidas a travĂ©s de la superficie terrestre o mediante satĂ©lites repetidores. Hasta ahora la mayorĂ­a de estos sistemas se ha basado en estĂĄndares tecnolĂłgicos maduros y testeados, los cuales se han adaptado con el fin de satisfacer las necesidades especĂ­ficas de cada misiĂłn y cliente. Sin embargo, las tendencias actuales en el diseño de los nuevos programas espaciales indica que un cambio de paradigma es necesario: una red espacial a imagen de Internet permitirĂ­a incrementar la capacidad y fiabilidad de las comunicaciones interplanetarias y, a la vez, reducir dramĂĄticamente sus costes. En este contexto, el paradigma de arquitectura de sistemas puede ser un buen punto de partida. Mediante la descomposiciĂłn formal del sistema, puede ayudar a determinar las decisiones que tienen un impacto cabal en el diseño de la arquitectura asĂ­ como identificar las ĂĄreas con tecnologĂ­as similares y de menor coste. Esta tesis presenta un marco teĂłrico general para evaluar sistemas de comunicaciones espaciales para misiones que orbitan la Tierra. Adicionalmente, la tesis indica los principales orĂ­genes de complejidad durante el modelado del sistema y presenta una discusiĂłn sobre la validez de anteriores estrategias para analizar el problema. En concreto, propone una comparaciĂłn de anteriores modelos respecto el paradigma de arquitectura de sistemas y su grado de adecuaciĂłn para evaluar y comprar arquitecturas. A continuaciĂłn, la tesis introduce un modelo computacional para simular y evaluar el rendimiento de sistemas de repetidores por satĂ©lite. La herramienta utiliza un rule-based expert system especĂ­ficamente diseñado con el fin de almacenar los principales elementos constitutivos de la arquitectura y comprender las interacciones lĂłgicas entre ellos. AnĂĄlogamente, el modelo usa mĂ©todos numĂ©ricos con el fin de calcular la evoluciĂłn temporal de la topologĂ­a de la red en un determinado intervalo de tiempo, asĂ­ como su capa fĂ­sica y un posible programa de contactos. En concreto, presenta un nuevo scheduler heurĂ­stico que garantiza la correcta ordenaciĂłn de las misiones y servicios a la vez que asegura un tiempo computacional aceptable.[CATALÀ] L'inici de la cursa espacial va iniciar-se l'any 1957 amb el llançament i operaciĂł del primer satĂšl·lit artificial, l'Sputnik 1 de la URSS. Des d'aleshores s'han dut a terme mĂșltiples programes espacials que han portat al lĂ­mit tant la tecnologia com la ciĂšncia i han permĂšs desvelar els misteris de l'univers. En tots aquests casos, la necessitat de sistemes de comunicaciĂł flexibles i fiables ha sigut primordial per tal d'assegurar el retorn de les dades cientĂ­fiques recopilades i, en certs casos, garantir el benestar i seguretat dels astronautes. Com a conseqĂŒĂšncia, mĂșltiples xarxes de comunicacions espacials han sigut desplegades, ja sigui a travĂ©s d'antenes globalment distribuĂŻdes a travĂ©s de la superfĂ­cie terrestre o mitjançant satĂšl·lits repetidors. Fins ara la majoria d'aquests sistemes s'han basat en estĂ ndards tecnolĂČgics madurs i testats, els quals s'han adaptat per tal de satisfer les necessitats especĂ­fiques de cada missiĂł i client. AixĂČ no obstant, les tendĂšncies actuals en el disseny dels nous programes espacials indica que un canvi de paradigma Ă©s necessari: una xarxa espacial a imatge d'Internet permetria incrementar la capacitat i fiabilitat de les comunicacions interplanetĂ ries i, alhora, reduir dramĂ ticament els seu costs. En aquest context, el paradigma d'arquitectura de sistemes pot ser un bon punt de partida. Mitjançant la descomposiciĂł formal del sistema, pot ajudar a determinar les decisions que tenen un impacte cabdal en el disseny de l'arquitectura aixĂ­ com permetre identificar Ă rees amb tecnologies similars i de menor cost. Aquesta tesi presenta un marc teĂČric general per avaluar sistemes de comunicacions espacials per missions orbitant la Terra. Addicionalment, la tesi indica els principals orĂ­gens de complexitat durant el modelatge del sistema i presenta una discussiĂł sobre la validesa d'anteriors estratĂšgies per analitzar el problema. En concret, proposa una comparaciĂł d'anteriors models respecte el paradigma d'arquitectura de sistemes i el seu grau d'adequaciĂł per avaluar i comparar arquitectures. A continuaciĂł, la tesi introdueix un model computacional per simular i avaluar el rendiment de sistemes de repetidors per satĂšl·lit. L'eina empra un rule-based expert system especĂ­ficament dissenyat per tal d'emmagatzemar els principals elements constitutius de l'arquitectura i comprendre les interaccions lĂČgiques entre ells. AnĂ logament, el model utilitza mĂštodes numĂšrics per tal de calcular l'evoluciĂł temporal de la topologia de la xarxa en un determinat interval de temps, aixĂ­ com calcular la seva capa fĂ­sica i un possible programa de contactes. En concret, presenta un nou scheduler heurĂ­stic que garanteix la correcte ordenaciĂł de les missions i serveis tot assegurant un temps de computaciĂł acceptable

    A study on mobile ad hoc networks equipped with free-space optical capabilities.

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    A mobile ad hoc network (MANET) offers a cost-effective solution for communications in areas where infrastructure is unavailable, e.g. emergency response, disaster recovery, and battlefield scenarios. Traditional MANETs operate in the radio frequency (RF) spectrum, where the available bandwidth is facing the challenge of the rapidly increasing demands. Free-space optics (FSO) provides an attractive complement to RF wireless MANETs because of its high bandwidth and interference-free operation. An effort to combine the main advantages of MANET and FSO technologies by equipping the network nodes with hybrid communications capabilities will be presented. Computer models of such a network were created using the network simulator OPNET Modeler. Various indicators of network performance, including packet loss ratio, end-to-end delay, throughput, etc. were obtained through simulation and examined. The analysis will be of significant assistance in the design and implementation of such next-generation MANETs

    Ethernet Fronthaul and Time-Sensitive Networking for 5G and Beyond Mobile Networks

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    Ethernet has been proposed to be used as the transport technology in the future fronthaul network. For this purpose, a model of switched Ethernet architecture is developed and presented in order to characterise the performance of an Ethernet mobile fronthaul network. The effects of traditional queuing regimes, including Strict Priority (SP) and Weighted Round Robin (WRR), on the delay and delay variation of LTE streams under the presence of background Ethernet traffic are investigated using frame inter-arrival delay statistics. The results show the effect of different background traffic rates and frame sizes on the mean and Standard Deviation (STD) of the LTE traffic frame inter-arrival delay and the importance of selecting the most suitable queuing regime based on the priority level and time sensitivity of the different traffic types. While SP can be used with traffic types that require low delay and Frame Delay variation (FDV), this queuing regime does not guarantee that the time sensitive traffic will not encounter an increase in delay and FDV as a result of contention due to the lack of pre-emptive mechanisms. Thus, the need for a queuing regime that can overcome the limitations of traditional queuing regimes is shown. To this extent, Time Sensitive Networking (TSN) for an Ethernet fronthaul network is modelled. Different modelling approaches for a Time Aware Shaper (TAS) based on the IEEE 802.1Qbv standard in Opnet/Riverbed are presented. The TAS model is assumed to be the scheduling entity in an Ethernet-based fronthaul network model, located in both the Ethernet switches and traffic sources. The TAS with/without queuing at the end stations has been presented as well. The performance of the TAS is compared to that of SP and WRR and is quantified through the FDV of the high priority traffic when this contends with lower priority traffic. The results show that with the TAS, contentioninduced FDV can be minimized or even completely removed. Furthermore, variations in the processing times of networking equipment, due to the envisaged softwarization of the next generation mobile network, which can lead to time variation in the generation instances of traffic in the Ethernet fronthaul network (both in the end-nodes and in switches/aggregators), have been considered in the TAS design. The need for a Global Scheduler (GS) and Software Defined Networking (SDN) with TAS is also discussed. An Upper Physical layer functional Split (UPS), specifically a pre-resource mapper split, for an evolved Ethernet fronthaul network is modelled. Using this model and by incorporating additional traffic sources, an investigation of the frame delay and FDV limitations in this evolved fronthaul is carried out. The results show that contention in Ethernet switch output ports causes an increase in the delay and FDV beyond proposed specifications for the UPS and other time sensitive traffic, such as legacy Common Public Radio Interface (CPRI)-type traffic. While TAS can significantly reduce or even remove FDV for UPS traffic and CPRI-type traffic, it is shown that TAS design aspects have to carefully consider the different transmission characteristics, especially the transmission pattern, of the contending traffic flows. For this reason, different traffic allocations within TAS window sections are proposed. Furthermore, it is demonstrated that increased link rates will be important in enabling longer fronthaul fibre spans (more than ten Kilometres fibre spans with ten Gigabit Ethernet links). The results also show that using multiple hops (Ethernet switches/aggregators) in the network can result in a reduction in the amount of UPS traffic that can be received within the delay and FDV specifications. As a result, careful considerations of the fibre span length and the number of hops in the fronthaul network should be made

    Telecommunications Networks

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    This book guides readers through the basics of rapidly emerging networks to more advanced concepts and future expectations of Telecommunications Networks. It identifies and examines the most pressing research issues in Telecommunications and it contains chapters written by leading researchers, academics and industry professionals. Telecommunications Networks - Current Status and Future Trends covers surveys of recent publications that investigate key areas of interest such as: IMS, eTOM, 3G/4G, optimization problems, modeling, simulation, quality of service, etc. This book, that is suitable for both PhD and master students, is organized into six sections: New Generation Networks, Quality of Services, Sensor Networks, Telecommunications, Traffic Engineering and Routing

    Performance Analysis of a Cooperative Search Algorithm for Multiple Unmanned Aerial Vehicles under Limited Communication Conditions

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    This research investigates the impacts of realistic wireless communications upon a group of unmanned aerial vehicles (UAVs) utilizing a distributed search algorithm. The UAVs are used to survey an area for mobile targets and they require communication to cooperatively locate the targets. The mobile targets do not continually radiate energy, which exacerbates the search effort; a UAV could fly directly over a target and not detect it. A simulation of cooperative UAVs is implemented using the OPNET Modeler network simulation tool. The search performance of a group of UAVs is observed when communication range, data rate, and the number of UAVs are varied. The performance is evaluated based on the total time it takes for the UAVs to completely detect all the targets in a given search area, the number of times internal areas are scanned, the amount of communication throughput achieved, the network traffic generated, network latency, and number of network collisions. The results indicate that the number of UAVs was found to have the greatest impact on the group\u27s ability to search an area, implying that the data shared between the UAVs provides little benefit to the search algorithm. In addition, it was found that a network with a 100 Kbps or faster data rate should allow for minimal congestion and a large degree of scalability. The findings demonstrate that the proposed four-stage search algorithm should operate reasonably well under realistic conditions
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