Earth resources technology satellite spacecraft system design studies. Volume 1 - Systems studies Final report

Earth Resources Technology Satellite System design studie

AAS/GSFC 13th International Symposium on Space Flight Dynamics

This conference proceedings preprint includes papers and abstracts presented at the 13th International Symposium on Space Flight Dynamics. Cosponsored by American Astronautical Society and the Guidance, Navigation and Control Center of the Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination, and control; attitude sensor calibration; attitude dynamics; and mission design

Algoritmos en transmisión y recepción para OFDM en entornos multi-usuario

Desde su incursión en la vida de los ciudadanos de forma cotidiana, las comunicaciones móviles han ido adquiriendo cada vez más protagonismo. Lo que hace unos años era un elemento de lujo o causa de envidias, hoy es algo tan habitual como coger el autobús. Este auge en las comunicaciones móviles ha llevado consigo un aumento del número de usuarios de estos servicios, así como una mayor exigencia por parte de éstos en cuanto a velocidad de transmisión, seguridad, servicios, calidad ... Por este motivo, se han ido introduciendo nuevas redes, así como mejoras en las ya existentes. Actualmente estamos asistiendo al inicio de la implantación de las redes denominadas de tercera generación (3G). No obstante, estas redes 3G fueron de nidas a mediados de los años 90. En la actualidad nos encontramos en la de nición de lo que será la cuarta generación móvil (4G) a la que probablemente preceda una intermedia, tal vez Super 3G. Muchas son las tecnologías candidatas para esta Super 3G o para la 4G, pero es OFDM (Multiplexación por División en Frecuencias Ortogonales - Orthogonal Frequency Division Multiplexing) una de las más prometedoras para terminar siendo la tecnología elegida, debido principalmente a la robustez que ofrece frente al multi-trayecto, la flexibilidad que proporciona por el hecho de dividir el ancho de banda en sub-portadoras que pueden ser moduladas independientemente para adaptarse a las condiciones específicas de los canales móviles y al aprovechamiento de la diversidad multi-usuario cuando se combina en OFDMA (Acceso múltiple por división en frecuencias ortogonales - Orthogonal Frequency Division Multiple Access). Sin embargo, para que estos sistemas OFDMA sean una realidad en redes futuras como la Super 3G o la 4G, es preciso reducir la complejidad que ellos conllevan, en aspectos como la sincronización multi-usuario o la implementación de la modulación adaptativa. Esta Tesis está enfocada a reducir la complejidad de implementación para que la tecnología OFDMA pueda ser un hecho en las futuras redes inalámbricas. La sincronización en sistemas OFDMA, principalmente en escenarios ad-hoc plantea un reto importante a la hora de implementarla en este tipo de redes. Dado que existe una literatura extensa dedicada a resolver el problema de la sincronización en entornos OFDM mono-usuario, en esta Tesis se propone un procedimiento para reducir el problema de la sincronización multiusuario al caso mono-usuario, lo que permite la re-utilización de todas las técnicas propuestas en la literatura. Además de las buenas prestaciones incluso en situaciones de saturación de la red, permite un ahorro de la energía necesaria para la realización de las tareas de sincronización. Asimismo, a la vez que se resuelve la sincronización multi-usuario, también en esta Tesis se aporta un algoritmo para realizar el seguimiento de la desviación de frecuencia en sistemas tanto OFDM como OFDMA, de una forma sencilla y eficiente. Este algoritmo utiliza las sub-portadoras piloto de los símbolos, y ofrece unas prestaciones razonables, incluso cuando el número de estas sub-portadoras piloto es reducido. La modulación adaptativa u otras técnicas avanzadas de comunicaciones como MIMO (Multiple Input Multiple Output) o el conformado de haz (beamforming), que se hacen más atractivas cuando se combinan con OFDM u OFDMA, requieren de cierta realimentación hacia el transmisor por parte del receptor, además de un conocimiento del canal bastante preciso. En esta Tesis se aportan algoritmos para la compresión de esta información (que puede ser muy elevada dependiendo de la granularidad de la adaptación y la variabilidad del canal), lo que permite un mejor aprovechamiento de los recursos radio, y simpli ca la implementación de este tipo de sistemas. Se consiguen reducciones superiores a cuatro veces la tasa original, lo que implica grandes ventajas en todos los sentidos. Además, se realiza un estudio teórico sobre cómo afectan los errores en la estimación de canal en la capacidad del sistema, obteniéndose dos cotas numéricas para ésta. Gracias a estas cotas se puede concluir que las técnicas actuales de estimación de canal son su cientemente buenas como para que las pérdidas producidas por los errores en esta estimación no sean muy significativas; No obstante, estas pérdidas aumentan a medida que se incrementa la relación señal a ruido, y, por tanto, es conveniente seguir mejorando la estimación de canal si se pretende que estos sistemas trabajen a altas relaciones señal a ruido. Por último, destacar que las simulaciones llevadas a cabo para examinar las prestaciones de los algoritmos desarrollados han proporcionado datos prácticos que ayudarán al diseño e implementación de futuras redes móviles 4G.Nowadays mobile communications are common in our society. In less than two decades they have changed the way people understand personal communications. This interest is still growing and makes users (every day larger in number) ask for more and more services, speed, security and quality, at least comparable to the wired technologies. For this reason, new networks have been introduced in the scene, as well as improvements in the already existing ones. At the moment we are witnessing the beginning of the deployment of the so-called third generation networks (3G). However, these 3G networks were defined in the middle of years 90. At the present time we are in the definition of what will be the fourth mobile generation, which is called the 4G and probably an intermediate stage as Super 3G could be defined first. Many different technologies are in consideration, but OFDM (Orthogonal Frequency Multiplexing Division) is one of most promising candidates to end up becoming the technology to be used, due mainly to the robustness that it others to the multi-path channel, the flexibility that it provides by the fact that it divides the bandwidth into sub-carriers which can be modulated independently to adapt the signal to the specific channel conditions and to the advantage of the multi-user diversity when it is used to multiplex several users in the form of OFDMA (Orthogonal Frequency Division Multiple Access). Nevertheless, in order for these OFDMA systems to be a reality in future networks as Super 3G or 4G, the reduction in complexity has to be considered, in aspects such as the multi-user synchronization or the implementation of the Adaptive Modulation. This doctoral Thesis is focused on reducing the implementation complexity in both multi-user synchronization and Adaptive Modulation so that OFDMA technology can be a fact in the near future radio networks. The synchronization in OFDMA systems, specially in ad-hoc scenarios, raises an important challenge at the time of implementing this technology. Since an extensive literature is devoted to solve the problem of the synchronization in single-user OFDM systems, in this Thesis we have designed and proposed a procedure to reduce the multi-user synchronization problem to the single-user case, and therefore it allows the reuse of all the already proposed techniques in the literature. The procedure exhibits a good performance even in network saturation situations, and in addition it does not incur in a high power consumption when performing the synchronization tasks. Besides, solving the multi-user synchronization problem, the Thesis also proposes an algorithm for frequency offset tracking in an efficient and simple way, for both OFDM and OFDMA systems. This algorithm uses the pilot sub-carriers scattered in each OFDM symbol, and o ers reasonable performance, even when the number of these pilot sub-carriers is small. Adaptive Modulation and other advanced techniques as MIMO (Multiple Input Multiple Output) or beamforming become more attractive when they are combined with OFDM or OFDMA. However they require certain feedback information from receiver to the transmitter, and in addition, a quite precise knowledge about channel conditions. In this Thesis several algorithms for compressing the feedback information have been developed. This feedback information can be very highly demanding (depending on the granularity of the adaptation and the variability of the channel), and therefore this compression allows a better use of the resources, and simplifies the implementation of this kind of systems. Reductions of more than four times the original flow are obtained, which implies great advantages. In addition, a theoretical study is made on how errors in channel estimation affect the channel capacity, and several upper-bounds (one of them very tight) for this effect are obtained. One of the conclusions is that the actual state of the art in channel estimation techniques is good enough to be used without too much loss; However, the loss increases as the signal to noise ratio increases, and therefore, it is suggested to continue improving channel estimation algorithms for improving performance in high signal to noise ratio scenarios. Finally, thanks to simulations and designs carried out in order to examine the performance of the developed algorithms, some practical data are provided that will help in the future design of new mobile networks as 4G

The Frankfurt School : the crisis of subjectivity and the problem of social change

The crisis of subjectivity and the problem of social change is the underground history of the European Revolution of 1917-23. Its final signal in the inter-war years came with the defeat of the Republican forces in the Spanish Civil War in the years preceding the Second World War. The defeats of progressive social forces in the inter-war years, leading to the catastrophe of the Second World War and the Holocaust brought the original Western Marxists into a socio-political terrain involving new developments and unexpected setbacks in the struggle for a rational society (socialism). Stalinism and Fascism blocked the route to socialist democracy on an international scale.In the dialectic of hope and despair the Second World War can be understood as representing the great terminus of accumulated defeats of the working class internationally in the inter-war period. For the Frankfurt School the Second World War was not only the lowest point humanity had reached at the height of technical progress, the sheer technological efficiency of the destructiveness it unleashed seemed to foreclose any impetus for optimism. Hope and despair, progress and reaction, became increasingly intertwined and at times impossible to distinguish in the succession of events. For Horkheimer and Adorno this was the dialectic of Enlightenment, the apotheosis of Western rationality dominating and consuming its own progress in an orgy of regression leading to barbarism. Midnight in the twentieth century became, for Horkheimer and Adorno at least, the eclipse of reason itself.The Frankfurt School, it has been argued here, expresses a tendency of Western Marxism and has to be analysed in this context. The notion that Western Marxism and thus the Frankfurt School were a simple product of defeat has been shown to be mistaken and ultimately dismissive of the complex interplay between theory, politics, and history. For the events in the inter-war years did not 'give rise to' the Frankfurt School as if thought were merely a reflection of historical events. The critique of orthodox Marxism must be applied to the sociology of the Frankfurt School: in other words, thought is not an 'affect' propelled by historical laws. The examination of the role of philosophy in the restoration of the subjective factor in ideology critique and the analysis of social change - and hence the reconstruction of the Marxian project - has shown that the Frankfurt School's major contribution to such a reconstruction was in restoring the dynamic concept of subjectivity as pioneered by Marx and Engels in The German Ideology [1845/46].This study has attempted to show the continued relevance of this School of Western Marxism in terms of its contribution to solving the crisis of subjectivity and the problem of social change, and as an important guide in the struggle for a humanist renaissance of Marxian socialism which, it has been argued, forms the essential dimension of this solution

\u3ci\u3eKabul Times\u3c/i\u3e, May 1974

Kabul Times, May 1974 *This is a large file and may take a couple of minutes to download

The Muslim intelligentsia of Indonesia : a genealogy of its emergence in the 20th century

This thesis examines 'the genealogy of Muslim intelligentsia (and power) in twentieth century Indonesia'. The main concern of the thesis is with the genealogy of the collective entity of Muslim 'intelligentsia'. Even so, attention will also be given to the role of individual 'intellectuals' as fomulators and articulators of the Muslim intelligentsia's collective identities and ideologies. Although the Indonesian intelligentsia has been the ruling stratum of Indonesian society, there has been no single systematic study under the rubric of Indonesian (Muslim) 'intelligentsia'. The very few available studies related to this issue have used the term Indonesian (Muslim) 'intellectuals' but have examined the ideas of individual intellectuals rather than provide an analysis of the structural position and collective representation of the Indonesian people of ideas. To a certain degree, Indonesian intelligentsia has been studied under the rubric of the Indonesian 'elite'. The mainstream analysts of the Indonesian elite tended to restrict the notion of power struggle to the purely political and bureaucratic fields, while power struggle in the realm of knowledge and meaning was not taken into serious consideration. Based on the assumption that Indonesian Muslims had frequently failed to win elections and control parliament, many analysts came to the conclusion that Muslim politics had been defeated. Moreover, most of these studies focused too much attention on individual time, without considering the time of the 'longue durée'. In considering intellectual performance and politics as an end product rather than as a process, as a synchronic state rather than as a diachronic development, these studies underestimated the regenerative capacity of Muslim intelligentsia. Such a conclusion is problematic in the context of the current preponderance of Muslim intelligentsia in the political and bureaucratic elite. This thesis is a dynamic, interactive and intertextual approach to the study of Indonesian Muslim intelligentsia and its relations to power. The dynamic approach of this thesis attempts to situate synchronic states within a diachronic context. This approach reveals that throughout the 20th century there have been diachronic Muslim intellectual networks across generations that made possible the continuity of Muslim intellectual political traditions. At the same time, there have been continuous synchronic changes in the formulation of Muslim intelligentsia's identities and ideologies across generations. The interactive approach of this study attempts to see the development of Muslim intelligentsia and power as the result of a dynamic interplay between past and present, between and within various intellectual-political traditions, and between various arenas of power relations. This approach reveals that ideological formulation and power strategies of a particular generation of Muslim intelligentsia cannot be isolated from the influence of the previous generation, the presence of significant others and the interplay of various arenas of power relations. The intertextual approach of this study attempts to mobilise interdisciplinary studies and to sec the interconnectedness of texts and discourse. This approach reveals the interdependence of inter-generaticnal texts of Muslim intelligentsia and the relationality of diverse texts as well as of discursive and non-discursive formations