[pt] Em comunicações Via-Satélite, o regime de chuvas brasileiro se apresenta como fator limitante na análise da viabilidade de redes VSAT (Very Small Aperture Terminal) nas bandas Ka e Ku. O objetivo do trabalho é analisar a indisponibilidade por chuvas de redes VSAT com topologia em estrela usadas no Brasil para determinados serviços, tais como telefonia e transmissão de dados e TV, utilizando-se cenários hipotéticos em termos da localização das estações terminais, de satélites com transponders nas bandas Ka e Ku e das características reais dos equipamentos e sistemas. Um dos objetivos dentro deste tema foi a análise da influência do modelo de atenuação. Para tal foram utilizadas as duas últimas versões de modelo de atenuação por chuvas que tem sido recomendado pela UIT-R para aplicações em Engenharia. Complementando este objetivo, analisou-se também a influência de dados de taxas de precipitação para o Brasil utilizado nestes modelos, tendo sido utilizadas duas fontes: a Recomendação P.837 do UIT-R e medidas regionais realizadas pelo CETUC. Outro objetivo foi à comparação entre os valores estimados de indisponibilidade com limites máximos recomendados o que permite obter conclusões sobre a viabilidade destes sistemas no Brasil. Complementado o estudo acima descrito, um segundo caso foi analisado correspondendo a um sistema DVBS. O cenário é composto de outro satélite (PAS-9), porém com as mesmas configuração (rede VSAT e topologia em estrela) e estações terrenas com mesmas localizações. A diferença em relação ao primeiro caso reside principalmente na maior taxa de transmissão e por ter sido utilizado na análise da indisponibilidade um modelo de atenuação por chuvas regional, desenvolvido pelo CETUC com base em dados de medidas no Brasil. Uma análise similar foi feita considerando o modelo atual da UIT-R para fins comparativos. / [en] In satellite communication, the Brazilians rains distributions are presented like limited factor in the viability analyze of VSAT networks (Very Small Aperture Terminal) in the bands Ka and Ku. The aim of the work is analyze the unavailable caused by VSAT rains with star topology used in Brazil to some kinds of service, like telephone and data transmission and TV, using conjectural scenes on the satellite s terminal stations with transponders in the bands Ka and Ku and the real characteristics of the equipments and systems. One of the objectives is analyze the influence of the attenuation system. For it were used the last two versions models rainy attenuation that has been recommended by UIT-R for applications in engineering. Completing this objective, were also analyzed the influence precipitation taxes data for Brazil using this models, have been used two fonts: the recommendation P.837 from UIT-R and regional measured realized by CETUC. Other objective was the comparison between unavailable esteem values with maxim limits recommended what allows having conclusions about the viability of these systems in Brazil. Concluding the study, a second case was analyzed corresponding a system. The scene is composed by from other satellite (PAS-9), by the way, with the same localizations. The difference between both are: the first one has a bigger tax of transmission for being used analyze of the unavailable one model of attenuation for regional rains, made by CETUC based on measure data from Brazil. One similar analyze was made considering an actual model of UTI-R for final comparisons.

Alternative means of satisfying the high bandwidth and protected communications requirements for New Construction Naval Surface Ships in the midst of conflicting reduced radar cross section (RCS) requirements were investigated using the systems engineering process. <p>Various antenna, ranging from parabolic dish antennas to Luneberg lens antennas to phased array antennas, and feed and amplifier combinations were considered to provide a dual-band Super High Frequency (SHF) and Extremely High Frequency (EHF) Satellite Communications (SATCOM) Terminal (SEST). <p>Through the design of this hypothetical system, the various stages of the systems engineering process are considered-- definition of need, conceptual design, preliminary system design, production and installation, and utilization and support. Sample tasks are performed at each stage in the process (e.g., a system performance specification is prepared in the advanced system planning stage). <p>The set of technical solutions that remained in the preliminary design phase are compared based on life cycle costs. Two approaches are recommended -- one assuming lowest life cycle cost has highest priority and one assuming that the ability to communicate simultaneously on SHF and EHF has highest priority. / Master of Science

This thesis describes the approach to designing a Low Earth Orbit CubeSat constellation capable of nearly constant coverage. The software package Satellite Tool Kit is used to create simulated multi-satellite systems that maintain a communication link between Tenby, Pembrokeshire, Wales and tactically chosen locations in the United States of America. The research will attempt to find the constellation capable of maintaining a set of design parameters (such as signal to noise ratio and altitude), with the minimum possible number of CubeSats. The downlink location, antenna design and the orbital planes are the negotiable parameters in the system, with little to no set constraints, and thus will be altered until the most favorable system is successfully designed.

As the need for more bandwidth increases, satellite communication (SatCom) terminals are forced to climb higher in frequency. Higher frequency means greater propagation losses, and so antenna gain and sensitivity have to increase. The higher the gain, the more difficult it is to point the antenna. To make matters even more challenging, consumers are requesting satellite links in harsher environments and on moving vehicle and planes. In order to meet today's challenges and improve on dish feeds, research is ongoing to replace fixed-beam feedhorns with smaller, cheaper, and lighter PCB based antennas and to develop low-cost electronically steered array feeds (ESAF). ESAFs will not only improve the signal link, but they will also aid in pointing the antenna and then tracking the satellite independent of movement. Here is presented some of the first planar antenna dish feeds developed by the Brigham Young University's SatCom Group. Included are the simulation and test procedures to determine if they are viable for SatCom use. The results show that these antennas make significant advancements in efficiencies and prove a path forward to a feedhorn replacement. Several planar designs are presented, each with a unique solution to meet all the requirements for a dish feed. Also presented is the first low-cost ESAFs developed to give commercial SatCom an electronically steerable dish. None of the designed hardware requires a redesign of current modems and receiver boxes. The research looks at keeping costs low by minimizing the required electronics. This further led to researching the limits on how simple the electronics could be. The ESAF doubled the visible area of the dish and successfully acquired and tracked a satellite as the dish moved. The ESAF also demonstrates a path forward to increase the steerable range and improve pointing and tracking.

No / Noise amplitude distribution measurements relevant to%satellite-mobile radio systems are reported. The rationale for the%measurements is outlined and the choice of measurement parameters%justified. The measurement equipment and measurement methodology are%described in detail. Results characterizing the elevation angle%distribution of impulsive noise are presented for rural, suburban and%urban environments and also for an arterial road (U.K. motorway)%carrying high density, fast moving traffic. Measurements of the levels%of impulsive noise to be expected in each environment for high- and%low-elevation satellite scenarios using appropriate antenna%configurations are also presented

Yes / Satellite communications represents a specialised area of telecommunications. While the development of satellite technology is relatively slow in comparison to wireless networks evolution, due to the need for high reliability, the services that satellites are able to offer are evolving at much the same pace as their terrestrial counterparts. It is within this context that the satellite communications network of excellence (SatNEx) has evolved its initiative, the aim being to serve the engineering community with the latest technological trends, while also providing a solid grounding in the fundamentals for those new to the subject area. / European Commission Framework Programme 6

Approved for public release, distribution is unlimited / Converging voice and data networks has the potential to save money and is the main reason Voice over Internet Protocol (VoIP) is quickly becoming mainstream in corporate America. The potential VoIP offers to more efficiently utilize the limited connectivity available to ships at sea makes it an attractive option for the Navy. This thesis investigates the usefulness of VoIP for the communications needs of a unit level ship. This investigation begins with a review of what VoIP is and then examines the ship to shore connectivity for a typical unit level ship. An OMNeT++ model was developed and used to examine the issues that affect implementing VoIP over this type of link and the results are presented. / Lieutenant Commander, United States Navy

Radio astronomy is used to study stars, galaxies, black holes and gas clouds radiation at radio frequencies. Detecting extremely weak signals from deep space radio sources requires high sensitive feed system associated with large dish antennas. The key figure of merit is survey speed, or the time required to map a region of the sky to a given source flux density. Survey speed is proportional to the frequency bandwidth, the field of view or observable region of the sky, and the squared sensitivity, where sensitivity is related to reflector aperture efficiency and system noise temperature. Compared to the traditional single feed, phased array feeds with significantly expanded field of view are considered as the next generation feed for radio telescope. This dissertation outlines the design, analysis and measurement of high sensitivity L-band and mm-wave phased array feeds for the 100-meter Green Bank Telescope. Theoretical works for radio astronomy includes design guideline for high sensitivity phased array feed, fundamental frequency bandwidth limit, array antenna loss influenced by mutual coupling and beamformer coefficients and possibility of superdirectivity for radio telescopes and other antennas. These study are helpful to understand and guide the design of a phased array feed system. In the absence of dish antennas, sparse phased arrays with aperiodic structure have been developed for satellite communications. A compromise between the peak side lobe level, array element density, directivity and design complexity is studied. We have found that the array peak side lobe level can be reduced by enhancing the array element direction at the main lobe direction, increasing the array element density and enlarging the array size. A Poynting streamline approach develops to understand the properties of a receiving antenna and the mutual coupling effects between array elements. This method has been successfully used to generate effective area shape for many types of antennas and guide the design of a superdirective antenna. Motivated by this method, a superdirective antenna is experimental demonstrated.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This project targeted the development of a new tracking collar, trap telemetry system and supporting infrastructure, to aid researchers from the Cape Leopard Trust. Previously used collar products had all proven insu cient in some capacity and remote monitoring of trap sites was also required. Tracking collars are used to identify the movement patterns of the leopards and through the resulting research, assist in protecting this threatened species. In the development of the tracking collar and trap telemetry system, a high level system design was rst formulated, identifying major components that would be required. Alternative methods for implementation were then considered and the most optimal chosen. Two di erent modes of communication with the collar were envisioned and designed for. These would be used to transmit logged coordinates obtained from a GPS receiver back to researchers. A VHF terrestrial radio link was investigated, but an Iridium Satellite based solution was ultimately selected. An Iridium Satellite communications system was also used for transfer of trap state data. Ultimately, a working trap telemetry system was delivered for use by researchers. The tracking collar system had progressed to a working prototype, requiring miniaturisation and packaging before deployment. A possible packaging solution was also identi ed. The trap telemetry system, although displaying certain de ciencies, provided a capability previously unavailable to researchers. With further development, there is potential for the tracking collar to provide accurate satellite tracking and communications in a mass and price combination not previously available. / AFRIKAANSE OPSOMMING: Hierdie projek het as doel die ontwikkeling van 'n nuwe opsporingshalsband, 'n lokval telemetriese stelsel en die nodige ondersteunende infrastruktuur daarvoor. As hulpmiddels vir navorsers van Cape Leopard Trust. Geen van die halsband produkte wat tot nou toe gebruik is, het voldoen aan al die nodige behoeftes nie, en dit was ook nodig om die lokvalterreine van 'n afstand te kan monitor. Die opsporingshalsbande word gebruik om die bewegingspatrone van luiperds vas te stel en die navorsing wat daarop volg, help dat 'n bedreigde spesie bewaar word. Die ontwikkeling van die opsporingshalsband en lokval telemetriese stelsel het begin met die formulering van 'n ho evlak stelselontwerp waarin die hoofkomponente wat benodig sou wees ge denti seer is. Alternatiewe metodes van bewerkstelling is daarna oorweeg en die optimale hiervan is gekies. Twee verskillende metodes van kommunikasie met die halsband is voorgestel en ontwerp. Hierdie sou gebruik word om die vasgelegte koordinate wat van 'n GPS ontvanger verkry is, na navorsers terug te versend. 'n Terrestriale radioverbinding is ondersoek, maar 'n Iridium Satelliet-baseerde oplossing is uiteindelik verkies. 'n Iridium Satelliet kommunikasie stelsel is ook gebruik vir die oordrag van data aangaande die lokvaltoestand. Uitendelik is 'n werkende lokval telemetriese stelsel gelewer vir dir gebruik van navorsers. Die opsporingshalsband stelsel was nou 'n werkende prototipe, wat slegs verklein en toepaslik verpak moes word voor dit in gebruik geneem kon word. 'n Moontlike oplossing tot die verpakkingsprobleem is ook identi seer. Die lokval telemetriese stelsel, hoewel dit steeds tekorte toon, voorsien die navorsers van voorheen onbekombare inligting. Met verder ontwikkeling is daar potensiaal vir die opsporingshalsband om akkurate satellietopsporing en kommunikasie te voorsien in 'n kombinasie van laer massa, sowel as prys, soos nog nooit voorheen beskikbaar nie.

Satellite communication system designers are continuously struggling to improve the channel capacity. A critical challenge results from the limited power available aboard the satellite.Because of this constraint, the onboard power amplifier must work with a small power supply which limits its maximum output power. To ensure a sufficient Signal-to-Noise power Ratio (SNR) on the receiver side, the power amplifier must work close to its saturation point. This is power efficient but unfortunately adds non-linear distortions to the communication channel. The latters are very penalizing for high order modulations.In the literature, several equalization algorithms have been proposed to cope with the resulting non-linear communication channel. The most popular solution consists in using baseband Volterra series in order to build non-linear equalization filters. On the other hand, the Recurrent Neural Networks (RNNs), which come from the artificial neural network field, are also interesting candidates to generate such non-linear filters. But they are difficult to implement in practice due to the high complexity of their training. To simplify this task, the Echo State Network (ESN) paradigm has been proposed. It has the advantage of offering performances similar to classical RNNs but with a reduced complexity.The purpose of this work is, first, to compare this solution to the state-of-the-art baseband Volterra filters. We show that the classical ESN is able to reach the same performances, evaluated in terms of Bit Error Rate (BER), and has similar complexity. Secondly, we propose a new design for the ESN which achieves a strong reduction in complexity while conserving a similar BER.To compensate for the channel, the literature proposes to adapt the coefficients of these equalizers with the help of a training sequence in order to recover the transmitted constellation points. We show that, in such a case, the usual symbol detection criterion, based on Euclidean distances, is no longer optimal. For this reason, we first propose a new detection criterion which meets the Maximum Likelihood (ML) criterion. Secondly, we propose a modification of the equalizers training reference points in order to improve their performances and make the detection based on Euclidean distances optimal again. This last solution can offer a significant reduction of the BER without increasing the equalization and detection complexity. Only the new training reference points must be evaluated.In this work, we also explore the field of analog equalizers as different papers showed that the ESN is an interesting candidate for this purpose. It is a promising approach to reduce the equalizer complexity as the digital implementation is very challenging and power-hungry, in particular for high bandwidth communications. We numerically demonstrate that a dedicated analog optoelectronic implementation of the ESN can reach the state-of-the-art performance of digital equalizers. In addition, we show that it can reduce the required resolution of the Analog-to-Digital Converters (ADCs).Finally, a hardware demonstration of the digital solutions is proposed. For this purpose, we build a physical layer test bench which depicts a non-linear communication between two radios. We show that if we drive the transmitter power amplifier close to its saturation point, we can improve the communication range if the non-linear distortions are compensated for at the receiver. The transmitter and the receiver are implemented with Software Defined Radios (SDRs). / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished