Physical and MAC layer techniques for next generation satellite communications

In this thesis, we consider four different scenarios of interest in modern satellite communications. For each scenario, we will propose the use of advanced solutions aimed at increasing the spectral efficiency of the communication links. First, we will investigate the optimization of the current standard for digital video broadcasting. We will increase the symbol rate of the signal and determine the optimal signal bandwidth. We will apply the time packing technique and propose a specifically design constellation. We will then compare some receiver architectures with different performance and complexity. The second scenario still addresses broadcast transmissions, but in a network composed of two satellites. We will compare three alternative transceiver strategies, namely, signals completely overlapped in frequency, frequency division multiplexing, and the Alamouti space-time block code, and, for each technique, we will derive theoretical results on the achievable rates. We will also evaluate the performance of said techniques in three different channel models. The third scenario deals with the application of multiuser detection in multibeam satellite systems. We will analyze a case in which the users are near the edge of the coverage area and, hence, they experience a high level of interference from adjacent cells. Also in this case, three different approaches will be compared. A classical approach in which each beam carries information for a user, a cooperative solution based on time division multiplexing, and the Alamouti scheme. The information theoretical analysis will be followed by the study of practical coded schemes. We will show that the theoretical bounds can be approached by a properly designed code or bit mapping. Finally, we will consider an Earth observation scenario, in which data is generated on the satellite and then transmitted to the ground. We will study two channel models, taking into account one or two transmit antennas, and apply techniques such as time and frequency packing, signal predistortion, multiuser detection and the Alamouti scheme.

A VERDADE É A CONVERSA: Aproximações inesperadas entre o neo-pragmatismo de Richard Rorty e a Teologia da Libertação em Juan Luis Segundo

Este estudo é uma tentativa de promover uma partilha de perspectivas entre o neo-pragmatismo do filósofo Richard Rorty, mormente a partir das obras Filosofia e o espelho da natureza e Contingência, Ironia e Solidariedade e a Teologia da Libertação, em seu mais proeminente representante, Juan Luis Segundo, com o foco principal nas obras Libertação da teologia e O dogma que liberta. Desenvolve-se aqui uma aproximação de olhares para a verdade e a revelação, concebendo-as como processos pedagógicos. A verdade, como conceito não apenas religioso, do que se busca para dar sentido ao mundo e a vida humana e a revelação, como uma experiência marcada pela linguagem e expectativas religiosas de significado existencial são experiências similares e constituem-se não como o resultado de um processo de aprendizagem, mas como o processo em si mesmo, aberto e em constante renovação. A verdade, assim, não seria aonde se chega, mas os caminhos pelos quais se vai. Encontrar os pontos de contato e as possíveis mútuas contribuições do pensamento do filósofo Richard Rorty, e sua filosofia edificante, e do teólogo Juan Luis Segundo, e sua ideia de revelação como processo pedagógico, será meu esforço de aproximação entre suas proposições e a construção de uma proposta que não fuja à linguagem e condição humanas. O humano, que marcado pela liberdade, tem na contingência de suas construções um limite para as suas conquistas e um espaço para a sua libertação de qualquer processo desumanizador.

Is the generation of neo-antigenic determinants by free radicals central to the development of autoimmune rheumatoid disease?

Biomolecules are susceptible to many different post-translational modifications that have important effects on their function and stability, including glycosylation, glycation, phosphorylation and oxidation chemistries. Specific conversion of aspartic acid to its isoaspartyl derivative or arginine to citrulline leads to autoantibody production in models of rheumatoid disease, and ensuing autoantibodies cross-react with native antigens. Autoimmune conditions associate with increased activation of immune effector cells and production of free radical species via NADPH oxidases and nitric oxide synthases. Generation of neo-antigenic determinants by reactive oxygen and nitrogen species ROS and RNS) may contribute to epitope spreading in autoimmunity. The oxidation of amino acids by peroxynitrite, hypochlorous acid and other reactive oxygen species (ROS) increases the antigenicity of DNA, LDL and IgG, generating ligands for which autoantibodies show higher avidity. This review focuses on the evidence for ROS and RNS in promoting the autoimmune responses observed in diseases rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). It considers the evidence for ROS/RNS-induced antigenicity arising as a consequence of failure to remove or repair ROS/RNS damaged biomolecules and suggests that an associated defect, probably in T cell signal processing or/or antigen presentation, is required for the development of disease.

Whither critical pedagogy in the neo-liberal university today? Two UK practitioners' reflections on constraints and possibilities

This paper, based on the reflections of two academic social scientists, offers a starting point for dialogue about the importance of critical pedagogy within the university today, and about the potentially transformative possibilities of higher education more generally. We first explain how the current context of HE, framed through neoliberal restructuring, is reshaping opportunities for alternative forms of education and knowledge production to emerge. We then consider how insights from both critical pedagogy and popular education inform our work in this climate. Against this backdrop, we consider the effects of our efforts to realise the ideals of critical pedagogy in our teaching to date and ask how we might build more productive links between classroom and activist practices. Finally, we suggest that doing so can help facilitate a more fully articulated reconsideration of the meanings, purposes and practices of HE in contemporary society. This paper also includes responses from two educational developers, Janet Strivens and Ranald Macdonald, with the aim of creating a dialogue on the role of critical pedagogy in higher education.

Neo-Nazism in West Germany

The oharaoter of right-wing extremism in the Federal Republic has undergone extensive transformations in the seventies. As electoral support for the extreme Right declined, a whole range of new groupings emerged pursuing a militant extra-parliamentary strategy. Essential charaoteristics are an increasing tendency to use violence and a close ideological affinity to the NSDAP. They attract a growing number of young people. The increasing susceptibility of young people to rightist ideologies coincides with an economic recession of which young people especially are the victims. Widespread ignorance about Nazism and the prevalence of anti-democratic political attitudes constitute important contributary factors and point to a considerable potential for right-extremism in the Federal Republic., This potential can be attributed. to the negative effects of much of the material dealing with the NS past, to serious deficiencies in the area of historical-political education in schools and, above all, to the absence of any :real process of "coming to terms with the past" in the postwar period. Neo-Nazism is not completely isolated from other trends in West German society. Rightist elements within the established party system and broad sections of the population hold similar views and attitudes. This similarity, linked with an over-exaggerated concern with a perceived threat from the extreme Left may explain the absence of any concerted effort to deal with nee-Nazi tendencies. The response of the courts exemplifies a widespread tendency to under-estimate the significance of the extreme Right. Opposition to the Right is restricted primarily to those circles which suffered most under the Nazi regime. The analysis suggests that one must reject the simplistic view that at the present time the Right does not constitute a serious threat to West German democracy. The study evaluates the wide range of views to be found in secondary sources on the subject of neo-Nazism and is :intended, to contribute to the ongoing discussion conceming the potential for right-extremism in West Germany.

A Kuhnian crisis in neo-Darwinism

Policy issues which receive large inputs of scientific and technical information are frequently marred by acrimonious controversies between contributing experts. There are few if any examples of a public policy decision being based on a firm consensus of scientific and technical experts. Such a consensus is taken for granted by the `Rational' model of decision making and its derivatives. Comparing the dynamics of conflict in policy-relevant issues with those of conflict in `pure' science, one is struck by their great similarity. In both cases we witness examples of rhetorical statements about incompetence, conflicting interpretations of data, and interdisciplinary communication problems. Noting this similarity, this thesis attempts to answer the question, `Is there a similarity of cause: do the same causes lie at the roots of conflict in policy-relevant and policy-irrelevant science?' In answering this question this thesis examines recent controversies in a generally policy-irrelevant science - evolutionary biology. Three episodes of conflict are studied: the `Neutral Allele Theory', `Punctuated Equilibrium', and `Structuralist versus Functionalist approaches to evolution'. These controversies are analysed in terms of both Kuhn's account of scientific `crises' and Collingridge and Reeve's (1986) `Overcritical Model'. Comparing its findings with those of Collingridge and Reeve, this thesis concludes that, (a) there is a Kuhnian crisis in contemporary evolution theory and, (b) that common causes do lie at the roots of conflict in policy-relevant and policy-irrelevant science. Science has an inherent tendency to degenerate into acrimonious conflict but at the same time has mechanisms which eventually resolve such conflicts. Unfortunately, when science is incorporated into the policy arena these mechanisms are prevented from operating. This thesis reinforces Collingridge and Reeve's conclusion that science is of little use to policy.

Performance investigation of IEEE 802.11 MAC in multihop wireless networks

Medium access control (MAC) protocols have a large impact on the achievable system performance for wireless ad hoc networks. Because of the limitations of existing analytical models for ad hoc networks, many researchers have opted to study the impact of MAC protocols via discreteevent simulations. However, as the network scenarios, traffic patterns and physical layer techniques may change significantly, simulation alone is not efficient to get insights into the impacts of MAC protocols on system performance. In this paper, we analyze the performance of IEEE 802.11 distributed coordination function (DCF) in multihop network scenario. We are particularly interested in understanding how physical layer techniques may affect the MAC protocol performance. For this purpose, the features of interference range is studied and taken into account of the analytical model. Simulations with OPNET show the effectiveness of the proposed analytical approach. Copyright 2005 ACM.

The French fifth Republic as an opportunity structure:a neo-institutional and cultural approach to the study of leadership politics

The Gaullist settlement of 1958 reconfigured the political institutions of France, introducing into the republican mainstream a new form of leadership politics. Adapting the literature on political opportunity structure (POS) theory, and using the French left as a case study, can help us understand how political parties, ideology and leadership adapt to political institutions and norms. It also illuminates what the consequences are of such adaptation in the contemporary period, particularly as regards the institutionally bound roles of political 'character', protocol and discourse. The paper appraises the relevance and appropriateness of POS theory to leadership politics in France.

An adaptive IEEE 802.15.4 MAC layer transmission scheme for applications with heterogeneous traffic

IEEE 802.15.4 networks has the features of low data rate and low power consumption. It is a strong candidate technique for wireless sensor networks and can find many applications to smart grid. However, due to the low network and energy capacities it is critical to maximize the bandwidth and energy efficiencies of 802.15.4 networks. In this paper we propose an adaptive data transmission scheme with CSMA/CA access control, for applications which may have heavy traffic loads such as smart grids. The adaptive access control is simple to implement. Its compatibility with legacy 802.15.4 devices can be maintained. Simulation results demonstrate the effectiveness of the proposed scheme with largely improved bandwidth and power efficiency. © 2013 International Information Institute.

The Cascade Neo-Fuzzy Architecture and its Online Learning Algorithm

In the paper learning algorithm for adjusting weight coefficients of the Cascade Neo-Fuzzy Neural Network (CNFNN) in sequential mode is introduced. Concerned architecture has the similar structure with the Cascade-Correlation Learning Architecture proposed by S.E. Fahlman and C. Lebiere, but differs from it in type of artificial neurons. CNFNN consists of neo-fuzzy neurons, which can be adjusted using high-speed linear learning procedures. Proposed CNFNN is characterized by high learning rate, low size of learning sample and its operations can be described by fuzzy linguistic “if-then” rules providing “transparency” of received results, as compared with conventional neural networks. Using of online learning algorithm allows to process input data sequentially in real time mode.

Performance optimisation of the MAC protocol with multiple contention slots in MIMO ad hoc networks

The multiple-input multiple-output (MIMO) technique can be used to improve the performance of ad hoc networks. Various medium access control (MAC) protocols with multiple contention slots have been proposed to exploit spatial multiplexing for increasing the transport throughput of MIMO ad hoc networks. However, the existence of multiple request-to-send/clear-to-send (RTS/CTS) contention slots represents a severe overhead that limits the improvement on transport throughput achieved by spatial multiplexing. In addition, when the number of contention slots is fixed, the efficiency of RTS/CTS contention is affected by the transmitting power of network nodes. In this study, a joint optimisation scheme on both transmitting power and contention slots number for maximising the transport throughput is presented. This includes the establishment of an analytical model of a simplified MAC protocol with multiple contention slots, the derivation of transport throughput as a function of both transmitting power and the number of contention slots, and the optimisation process based on the transport throughput formula derived. The analytical results obtained, verified by simulation, show that much higher transport throughput can be achieved using the joint optimisation scheme proposed, compared with the non-optimised cases and the results previously reported.

Turkey and neo-Ottomanism: Domestic sources, dynamics and foreign policy

This study examined the relationship between the Turkish Islamic movements and the present government of the Justice and Development Party ( Adalet ve Kalkinma Partisi, AK Party). Since the AK Party came to power in 2002 it implemented unparalleled political reforms and pursued to improve Turkey’s relations with the EU. Opponents argued that because of the dominance of the secular military in Turkish politics, the AK Party is forced to secretly advance its Islamic agenda using the language and symbolism of democracy and human rights. This study argued that the ideas of the AK Party show similarities with the “Ottomanist” thought of the late Ottoman era. With special reference to the preservation of the Ottoman State, Ottomanism in an eclectic way was able to incorporate Islamic principles like freedom, justice and consultation into the political arena which was increasingly dominated by the secular European concepts. Literature on Islam and politics in Turkey, however, disregards the Ottoman roots of freedom and pluralism and tends to reduce the relationship between religion and state into exclusively confrontational struggles. This conceptualization of the political process relies on particular non-Turkish Muslim experiences which do not necessarily represent Islam’s venture in Turkey. Contrary to the prevailing scholarship, Islamic movements in Turkey, namely, Naqshbandi, National View and Nur, which are discussed in detail in this study, are not monolithic. They all uphold the same creedal tenets of Islam but they have sharp differences in terms of how they conceptualize the role of religious agency in politics. I argue that this diversity is a result of three distinct methodologies of Islamic religious life which are the Tariqah (Tarikat ), Shariah (Şeriat), and Haqiqah ( Hakikat). The differences between these three approaches represent a typological hierarchy in the formation of the Muslim/believer as an agent of Islamic identity. Through these different if not conflicting modes, the AK Party reconnected itself with Turkey’s Ottoman heritage in a post-Ottoman, secular setting and was able to develop an eclectic political identity of Neo-Ottomanism that is evident in the flexibility if not inconsistency of its domestic and foreign policy preferences.