85 research outputs found

    Performance analysis of low earth orbit (LEO) satellite link in the presence of elevation angle, fading and shadowing

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    This thesis report is submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Computer Science and Engineering, 2009.Cataloged from PDF version of thesis report.Includes bibliographical references (page 65).Tanjila FarahPrianka RoyB. Computer Science and Engineerin

    Data Communication With A Nano-satellite Using Satellite Personal Communication Networks (s-pcns)

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    Satellites typically communicate with locations on the ground to receive commands and send data back. Establishing reliable communications generally requires dedicated ground stations, which in turn require hardware and expertise. Developers of nano-satellites, however, may not have the expertise or resources necessary for establishing a dedicated ground station. Therefore, the use of an existing communication system, such as the Satellite Personal Communication Networks (S-PCNs), is attractive. Another shortcoming of the fixed ground stations, already available, is that they are normally only able to communicate with Low Earth Orbit (LEO) nano-satellites four times per day (two10-minute windows separated by 90 minutes, followed 12 hours later by two more such 10-minute windows). This drawback is also overcome by the use of S-PCNs which provide increased access times, smaller gaps in contact between the satellites and ground stations, and easier tracking of satellite health. In this thesis, the capabilities of S-PCNs for communications with a nano-satellite are explored. Software simulation and analysis have been performed to assess system performance. Ground testing of the hardware is done to understand the use of such systems for small satellites

    Proceedings of the Fifth International Mobile Satellite Conference 1997

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    Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

    Band sharing and satellite diversity techniques for CDMA.

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    High levels of interference between satellite constellation systems, fading and shadowing are a major problem for the successful performance of communication systems using the allocated L/S frequency bands for Non-Geostationary Earth Orbit (NGEO) satellites. As free spectrum is nonexistent, new systems wishing to operate in this band must co-exist with other users, both satellite and terrestrial. This research is mainly concerned with two subjects. Firstly, band sharing between different systems Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) has been evaluated for maximizing capacity and optimising efficiency of using the spectrum available. For the case of widened channel bandwidth of the CDMA channel, the overlapping was tested under different degrees of channel overlap and different orders of filters. The best result shows that at the optimum degree of channel overlap, capacity increases by up to 21%. For the case of fixed channel bandwidth, the optimum overlapping between CDMA systems depends on the filtering Roll-off factor and achieves an improvement of the spectrum efficiency of up to 13.4%. Also, for a number of narrowband signal users sharing a CDMA channel, the best location of narrowband signals to share spectrum with a CDMA system was found to be at the edge of the CDMA channel. Simulation models have been constructed and developed which show the combination of DS- CDMA techniques, forward error correction (FEC) code techniques and satellite diversity with Rake receiver for improving performance of interference, fading and shadowing under different environments. Voice activity factor has been considered to reduce the effect of multiple access interference (MAI). The results have shown that satellite diversity has a significant effect on the system performance and satellite diversity gain achieves an improvement up to 6dB. Further improvements have been achieved by including concatenated codes to provide different BER for different services. Sharing the frequency band between a number of Low Earth Orbit (LEO) satellite constellation systems is feasible and very useful but only for a limited number of LEOS satellite CDMA based constellations. Furthermore, satellite diversity is an essential factor to achieve a satisfactory level of service availability, especially for urban and suburban environments

    Prediction of Satellite Shadowing in Smart Cities with Application to IoT

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    The combination of satellite direct reception and terrestrial 5G infrastructure is essential to guarantee coverage in satellite based-Internet of Things, mainly in smart cities where buildings can cause high power losses. In this paper, we propose an accurate and fast graphical method for predicting the satellite coverage in urban areas and SatCom on-the-move scenarios. The aim is to provide information that could be useful in the IoT network planning process, e.g., in the decision of how many terrestrial repeaters are really needed and where they should be placed. Experiments show that the shadowed areas predicted by the method correspond almost perfectly with experimental data measured from an Eutelsat satellite in the urban area of Barcelona.Ministerio de Industria, Turismo y Comercio de España TSI-020301-2009-3

    Quantifying technology infusion and policy impact on low earth orbit communication satellite constellations

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    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2004.Includes bibliographical references (p. 199-204).Technology infusion and policy implementation bring impacts to the trade space of complex engineering systems. This work describes in detail the frameworks for quantitative analyses on these impacts, demonstrates their use on the sample system, and presents the analysis results. The low earth orbit (LEO) communication satellite constellation system serves as the platform for carrying out the system trade space analysis. The system is reproduced in computer environment in the form of a multiple-input-output MATLAB model. The model contains multiple modules that incorporate the physics, economy, and policies of the real-world system. The inputs to the model are system design variables and the outputs are system performance, capacity, and cost. The Pareto optimal solution set of the baseline trade space is generated by the model using a full-factorial run that covers the entire design space. To simulate technology infusion, technical and cost attributes of four new technologies are quantified and infused into the system model. The infusion of technologies and combinations of technologies into the system is simulated. Policy implementation is simulated by changing the policy constraints in the model. The technology-infused trade space and policy-implemented trade space have new sets of Pareto optimal solutions. By comparing these solution sets with the baseline optimal solution set in the objective space, we can quantify the impact of technology infusion and policy impact. In conclusion, the methodologies of quantifying the impact of technology infusion and policy implementation on complex engineering systems is repeatable and has been tested against real-world systems.(cont.) The information generated demonstrates their usefulness to technology selection and policy decision-making processes.by Darren Datong Chang.S.M

    Space-Based Information Infrastructure Architecture for Broadband Services

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    This study addressed four tasks: (1) identify satellite-addressable information infrastructure markets; (2) perform network analysis for space-based information infrastructure; (3) develop conceptual architectures; and (4) economic assessment of architectures. The report concludes that satellites will have a major role in the national and global information infrastructure, requiring seamless integration between terrestrial and satellite networks. The proposed LEO, MEO, and GEO satellite systems have satellite characteristics that vary widely. They include delay, delay variations, poorer link quality and beam/satellite handover. The barriers against seamless interoperability between satellite and terrestrial networks are discussed. These barriers are the lack of compatible parameters, standards and protocols, which are presently being evaluated and reduced

    Handover and Channel Allocation Mechanisms in Mobile Satellite Networks

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    In this work we study first handover prediction in non-geostationary mobile satellite networks. The ultimate choice of the transition path depends on UT position and signal strength. We investigate the procedure of beam monitoring and propose UT maximum residence as the criterion for path selection. The UT must operate both in full- and half-duplex mode, the latter being desirable when power limitations are imposed. We propose a scheme that achieves this goal and guarantees efficient diversity provision. Constant delay contours on the earth's surface are defined. The problem of reliable time delay acquisition is addressed, in case synchronization is lost. The SBS solves that either by using the known estimate of UT position or by requesting a measurement report by the UT. The problem of channel allocation appears in cellular networks of every kind. Calls arising in the cell overlap area have access to channels of more than one base station and may choose which base station they will use to establish connection. In that case the problems of base station and channel assignment arise jointly. We address the problem in a linear cellular network and aim at the minimumnumber of utilized channels. We present two algorithms: The first one expands Load Balancing in clique populations and is Sequential Clique Load Balancing (SCLB). The second one is named Clique Load Balancing with Inverse Water-Filling (CLB-IWF). In a dynamic environment, we unify SCLB and CLB-IWF into CLB-DA, which comprises Dynamic Allocation. CLB-DA is compared with Least Loaded Routing (LLR) policy and with Random Routing policy. We finally deduce that at light loads CLB-DA outperforms LLR, attaining smaller blocking probability, whereas at heavier loads all three policies converge

    Distributed satellite communications system design : first-order interactions between system and network architectures

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    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.Includes bibliographical references (p. 159-165).Humanity now exists in the midst of the fast-moving Information Age, a period of history characterized by fast travel and even faster information transfer. As data becomes seemingly more valuable than physical possessions, the introduction of exciting applications for communications services becomes ever more critical for the success - and in some cases, survival - of businesses and even nations. While the majority of these innovations have occurred over cable and fiber, a number of the most socially significant have occurred due to the introduction of satellites. Terrestrial fiber and cable systems have a number of advantages, but the extent of their reach and the cost of installation - in terms of both capital and time - favor industrialized nations over more remote and underdeveloped communities. Even as satellites offer the only real chance for ultimate communications ubiquity and true global unity, there remains a significant cost-benefit barrier. Few commercial satellite systems have succeeded economically without first falling victim to bankruptcy. The upfront capital required to implement a satellite communications system is staggering, and historically satellite companies have failed to adequately match capacity and service options to the current and actual future demand. The design process itself is an inherent limiting factor to the achievable cost and performance of a system.(cont.) Traditionally, the first step toward designing satellite communication systems - as well as terrestrial, sensor web, and ad hoc networks - has been to specify the system topology (e.g., the orbits of the satellites and the locations of the ground stations) based on the desired market and then to design the network protocols to make the most of the available resources. Such a sequential process assumes that the design of the network architecture (e.g., protocols, packet structure, etc) does not drive the design of the system architecture (e.g., constellation topology, spacecraft design, etc). This thesis will show that in the case of Ka-band distributed satellite communication systems this fundamental assumption is not valid, and can have a significant impact on the success (cost, capacity, customer satisfaction) of the resulting satellite communication system. Furthermore, this thesis will show that how a designer values performance during the design and decision process can have a substantial impact on the quality of the design path taken through the trade space of possible joint architectures.by Jennifer E. Underwood.S.M
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