160,681 research outputs found
Ka-to-W Band EM Wave Propagation: Tropospheric Effects and Countermeasures
No full textNear future satellite and terrestrial telecommunication (TLC) systems are expected to benefit from the use of operational frequencies spanning the Ka, Q, V and W bands, the main advantages being the availability of larger bandwidths and the smaller antenna size for a given gain. Moreover, the possibility of using on-board antennas with enhanced directivity is attractive for satellite systems whose coverage area is subdivided into spot beams for frequency reallocation or regional services. For example, the W band is attractive for fixed satellite services (FSS), especially for geostationary high-throughput systems (HTSs), in which the use of such frequencies for the feeder link (i.e. large available bandwidth) could reduce significantly the number of gateways with respect to Ka and Q/V bands. As for deep space missions, the main driver for the interest in using frequencies in the Ka to W bands is the possible increase in the on-board antenna gain with respect to the values at X band considered for current or planned missions. The drawback of using electromagnetic waves at frequencies in Ka, Q, V and W bands is the definite impact of the impairments caused by the troposphere. As a consequence, the design of TLC systems at such frequencies, and in particular satellite-based ones, cannot rely on the classical approach of simply assigning an extra power margin to counteract atmospheric fades. The extensive use of fade mitigation techniques (FMTs), such as link power control (LPC), site diversity or on-board adaptive power allocation, from the propagation side, adaptive coding and modulation (ACM) and data rate adaptation (DRA), from the telecommunication side, is mandatory. A reduction of the quality of service (QoS) should also be considered. This chapter deals with all these aspects characterizing the propagation of electromagnetic waves in the Ka, Q, V and W bands, spanning from the main impairments induced by the troposphere (and how they change as the frequency increases), to how extreme atmospheric conditions can be handled making use of suitable FMTs
Tropospheric Attenuation: A Challenge for Future Earth-Space Communications Systems
No full textIn approximately 60 years, Earth-space communications have evolved from early broadcasting systems to the modern complex interactive ones able to deliver worldwide broadband coverage. This was made possible by the gradual transition of carrier frequencies from the S band (2-4 GHz) to the Ka band (26.5-40 GHz), which is still partially taking place. Unfortunately, the increase in the carrier frequency is also accompanied by the growing impact of the troposphere, which induces several negative effects, attenuation being the most detrimental one. If the troposphere already poses clear limitation to modern Earth-space communications, even more it will to future systems, which are foreseen to operate at even higher carrier frequencies. This contribution discusses such challenges, specifically targeting next generation Earth-space communication systems operating at V band (40-75 GHz), W band (75-110 GHz) and, possibly, even up to the sub-THz band
Effects of the age-related immune depression induced by MTV on the in vivo growth of a mammary carcinoma
No full textEfficient calculation of cloud attenuation for earth-space applications
No full textThis letter presents a simple and accurate approach to calculate cloud attenuation for Earth-space communication systems operating in the 20-200-GHz frequency range. The methodology relies on the use of the mass absorption coefficient for liquid water aW, which is assumed to be independent of the site of interest. This finding, inferred from an extensive set of radiosonde observations collected in 14 locations throughout Europe, allows to devise a simple expression for aW as function only of frequency and, consequently, to efficiently calculate cloud attenuation. This indeed represents the main advantage of the approach, which, as a result, can take full advantage of global datasets of integrated liquid water content W made available, for example, by Earth Observation sensors
Predicting cloud attenuation on Earth-space EHF links
No full textThis contribution presents a new approach to the prediction of cloud attenuation A on Earth-space links operating in the EHF (Extremely High Frequency) range. The methodology relies on SMOC (Stochastic MOdel of Clouds), which synthesizes high-resolution three-dimensional distributions of the liquid water content w (extent: 200 km×200 km horizontal, 10 km vertical), starting from coarse integral information typically provided by global gridded Numerical Weather Prediction products. Cloud attenuation statistics are calculated by coupling synthetic cloud fields with a simplified yet accurate approach to estimate cloud attenuation based on the concept of mass absorption coefficient. Tests performed against reference attenuation data inferred from an extensive set of radiosonde observations show a very satisfactory accuracy of the proposed methodology in estimating A and, on the other hand, a marked tendency to overestimation of the model currently adopted in recommendation ITU-R P.840-6
Prof. Th. W. Adorno and the author Hans Erich Nossack.
No full textProf. Th. W. Adorno and the author Hans Erich Nossack at a reception of Insel Verlag, Buchmesse Frankfurt 1966LB
The challenge of using the W band in satellite communication
No full textThis contribution outlines the scenario of the expected atmospheric impairments, which affect a satellite radio link
operating in the W band, as derived by the present theoretical and experimental knowledge. The paper discusses
the contributions to signal fade due to gases, clouds, scintillation and rain (with emphasis also on the impact of the
hydrometeor size distribution), as well as to the depolarization of the electromagnetic waves. The main objective is
to assess the constraints to face in the design of a satellite telecommunication system operating in the W band
Nowe spojrzenie na planowanie architektury mieszkaniowej w afryce subsaharyjskiej
No full textThe author shares his reflections on state of art in housing and urban planning, deficiencies, expectations and possibilities in the Sahel region of Africa. He notices, that the housing problem in Africa is one of the challenges, which should be solved in order to recover life dignity of African people and secure their rights to traditional family life in acceptable conditions. The paper describes the studies on the typical dispersed urban structures and the need to foster this type of settlement structure and proposals of introduction of new on light steel frame housing system in the area of Sahel, combining the traditional way of building houses with modern technology. The particularly analysed case, is the housing problem in the Republic of Chad. The author presents the basic discussion on this topic and his architectural proposals. Unfortunately, the gap between the needs and the financial feasibility of housing construction in this area, makes this project already at the starting point extremely difficult to be realized without external subventions.Problem mieszkaniowy w Afryce jest jednym z wyzwań, które należy rozwiązać, aby Afrykanie mogli odzyskać godność życiową i zabezpieczyć swoje prawa do tradycyjnego życia rodzinnego w akceptowalnych warunkach. W artykule opisano badania nad typowymi rozproszonymi strukturami miejskimi i potrzebą wspierania tego typu struktur osadniczych oraz propozycji wprowadzenia nowego systemu konstrukcji domów, opartym na lekkim szkielecie stalowym, łączącym tradycyjny sposób budowania domów z nowoczesną technologią. Przypadkiem szczególnie analizowanym jest problem mieszkaniowy w Republice Czadu. Autor przedstawia podstawową dyskusję na ten temat i swoje propozycje architektoniczne. Niestety luka między potrzebami mieszkaniowymi w Czadzie a finansową wykonalnością budownictwa mieszkaniowego w tym obszarze sprawia, że projekt ten, już w punkcie wyjścia, jest niezwykle trudny do realizacji bez uzyskania zewnętrznych dotacji
W-band Atmospheric Radiowave Propagation - A Challenge for Satellite TLC Systems
No full textThis contribution is aimed at presenting the scenario of the expected atmospheric impairments suffered by a radio link operating in the W band, as derived by the present theoretical and experimental knowledge. The contributions to signal fade due to gases, clouds, scintillation and rain (with emphasis also on the impact of the hydrometeor size distribution), as well as the melting layer characteristics and the depolarization of the electromagnetic waves are discussed. The main objective is to assess the constraints to face in the design of a satellite TLC system operating in the W band
Seeing the world anew : the radical vision of Martin Waldseemüller's 1507 & 1516 world maps /
No full text9781929154470 (ISBN). 192915447X (ISBN). First edition 2012. Accompanied by 2 foldeds map in front and back pockets: 1507 map -- 1516 map.; Includes bibliographical references: pages 98-107.; Maps from pockets also available online http://nla.gov.au/nla.map-vn6254227; Original version of the 1507 map: Universalis cosmographiae secundum Ptholomaei traditionem et Americi Vespucii alioru que lustrationes. [St. Dié, France? : s.n., 1507]; Original version of the 1516 map: Carta marina, navigatoria Portugallen, navigationes atque tocius cogniti orbis terre marisque formam naturamq[u]e situs et terminos nostris temporibus recognitos et ab antiquorum traditione differentes eciam quor[um] vetusti non meminerunt auctores hec generaliter indicat / consumatum est in oppido S. Deodati compositione et digestione Martini Waldseemuller Ilacomili. [St. Dié, France? : s.n., 1516]. Prologue: In a Renaissance Vision, a Glimpse of the Modern / John W. Hessler -- "An island surrounded on all sides by sea" : The World Map, 1507 / John W. Hessler -- "Land of Cuba, part of Asia" : The Carta marina, 1516 / Chet Van Duzer -- Epilogue: A Renaissance That Resonates Still / John W. Hessler -- Notes -- Afterword / Ralph E. Ehrenberg -- About the authors -- Acknowledgments -- The Maps: The 1507 World Map, 12 sheets, with commentary -- Composite: front pocket -- The 1516 Carta marina, 13 sheets, with commentary -- Composite: back pocket
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