913 resultados para 100508 Satellite Communications


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This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz. This is realized with the aid of the $\kappa-\mu$ / gamma composite fading model which assumes that the transmitted signal undergoes $\kappa-\mu$ fading which is subject to \emph{multiplicative} shadowing. Based on this, the total power of the multipath components, including both the dominant and scattered components, is subject to non-negligible variations that follow the gamma distribution. For this model, we present an integral form of the probability density function (PDF) as well as important analytic expressions for the PDF, cumulative distribution function, moments and moment generating function. In the case of indoor off-body communications, the corresponding measurements were carried out in the context of four explicit individual scenarios namely: line of sight (LOS) and non-LOS (NLOS) walking, rotational and random movements. The measurements were repeated within three different indoor environments and considered three different hypothetical body worn node locations. With the aid of these results, the parameters for the $\kappa-\mu$ / gamma composite fading model were estimated and analyzed extensively. Interestingly, for the majority of the indoor environments and movement scenarios, the parameter estimates suggested that dominant signal components existed even when the direct signal path was obscured by the test subject's body. Additionally, it is shown that the $\kappa-\mu$ / gamma composite fading model provides an adequate fit to the fading effects involved in off-body communications channels. Using the Kullback-Leibler divergence, we have also compared our results with another recently proposed shadowed fading model, namely the $\kappa-\mu$ / lognormal LOS shadowed fading model. It was found that the $\kappa-\mu$ / gamma composite fading model provided a better fit for the majority of the scenarios considered in this study.

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This paper investigates the potential improvement in signal reliability for indoor off-body communications channels operating at 5.8 GHz using switched diversity techniques. In particular we investigate the performance of switch-and-stay combining (SSC), switch-and-examine combining (SEC) and switch-and-examine combining with post-examining selection (SECps) schemes which utilize multiple spatially separated antennas at the base station. During the measurements a test subject, wearing an antenna on his chest, performed a number of walking movements towards and then away from a uniform linear array. It was found that all of the considered diversity schemes provided a worthwhile signal improvement. However, the performance of the diversity systems varied according to the switching threshold that was adopted. To model the fading envelope observed at the output of each of the combiners, we have applied diversity specific equations developed under the assumption of Nakagami-$m$ fading. As a measure of the goodness-of-fit, the Kullback-Leibler divergence between the empirical and theoretical probability density functions (PDFs) was calculated and found to be close to 0. To assist with the interpretation of the goodness-of-fit achieved in this study, the standard deviation, $\sigma$, of a zero-mean, $\sigma^2$ variance Gaussian PDF used to approximate a zero-mean, unit variance Gaussian PDF is also presented. These were generally quite close to 1 indicating that the theoretical models provided an adequate fit to the measured data.

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The pinewood nematode (PWN), Bursaphelenchus xylophilus , is a major pathogen of conifers, which impacts on forest health, natural ecosystem stability and international trade. As a consequence, it has been listed as a quarantine organism in Europe. A real-time PCR approach based on TaqMan chemistry was developed to detect this organism. Specific probe and primers were designed based on the sequence of the Msp I satellite DNA family previously characterized in the genome of the nematode. The method proved to be specific in tests with target DNA from PWN isolates from worldwide origin. From a practical point of view, detection limit was 1 pg of target DNA or one individual nematode. In addition, PWN genomic DNA or single individuals were positively detected in mixed samples in which B. xylophilius was associated with the closely related non-pathogenic species B. mucronatus , up to the limit of 0.01% or 1% of the mixture, respectively. The real-time PCR assay was also used in conjunction with a simple DNA extraction method to detect PWN directly in artificially infested wood samples. These results demonstrate the potential of this assay to provide rapid, accurate and sensitive molecular identification of the PWN in relation to pest risk assessment in the field and quarantine regulation.

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Esta tese apresenta um estudo sobre alguns dos protocolos de cooperação MAC para redes sem fios utilizando o sistema IEEE 802.11 multi-débito. É proposto um novo modelo de arquitetura para a categorização e análise da cooperação em redes sem fios, tendo este modelo sido aplicado a protocolos cooperativos existentes para camada MAC. É investigado como as características do meio físico, assim como os requisitos de níveis superiores podem ser aplicados ao processo de cooperação, com vista a melhorar as características de funcionamento da rede de comunicações. Para este propósito são exploradas as métricas mais relevantes para o processo de cooperação. São igualmente estudados os limites impostos pelos protocolos da camada MAC e as limitações práticas impostas por protocolos da família de normas que compõem o IEEE 802.11. Neste trabalho foi criada uma métrica multicamada, que permite considerar os requisitos aplicacionais de performance e o tipo de tráfego, assim como a mobilidade dos dispositivos, no funcionamento dos mecanismos de cooperação. Como forma de validação, e para corretamente avaliar o impacto da métrica, um novo protocolo de cooperação foi desenvolvido e implementado. O seu funcionamento é descrito de forma analítica assim como validado através de a um ambiente de simulação. Os resultados obtidos mostram que a utilização de uma métrica multicamada é uma técnica robusta, fornecendo melhorias consistentes no contexto de redes IEEE 802.11. São igualmente demonstradas várias outras características de funcionamento com impacto para as comunicações. Estes dados fornecem uma visão real e encorajadora para a realização de mais pesquisas para a melhoria da performance dos protocolos cooperativos, assim como a sua utilização num variado número de aplicações futuras. No final do documento são apresentados alguns desafios para a continuação da investigação deste tópico.

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Wireless communication technologies have become widely adopted, appearing in heterogeneous applications ranging from tracking victims, responders and equipments in disaster scenarios to machine health monitoring in networked manufacturing systems. Very often, applications demand a strictly bounded timing response, which, in distributed systems, is generally highly dependent on the performance of the underlying communication technology. These systems are said to have real-time timeliness requirements since data communication must be conducted within predefined temporal bounds, whose unfulfillment may compromise the correct behavior of the system and cause economic losses or endanger human lives. The potential adoption of wireless technologies for an increasingly broad range of application scenarios has made the operational requirements more complex and heterogeneous than before for wired technologies. On par with this trend, there is an increasing demand for the provision of cost-effective distributed systems with improved deployment, maintenance and adaptation features. These systems tend to require operational flexibility, which can only be ensured if the underlying communication technology provides both time and event triggered data transmission services while supporting on-line, on-the-fly parameter modification. Generally, wireless enabled applications have deployment requirements that can only be addressed through the use of batteries and/or energy harvesting mechanisms for power supply. These applications usually have stringent autonomy requirements and demand a small form factor, which hinders the use of large batteries. As the communication support may represent a significant part of the energy requirements of a station, the use of power-hungry technologies is not adequate. Hence, in such applications, low-range technologies have been widely adopted. In fact, although low range technologies provide smaller data rates, they spend just a fraction of the energy of their higher-power counterparts. The timeliness requirements of data communications, in general, can be met by ensuring the availability of the medium for any station initiating a transmission. In controlled (close) environments this can be guaranteed, as there is a strict regulation of which stations are installed in the area and for which purpose. Nevertheless, in open environments, this is hard to control because no a priori abstract knowledge is available of which stations and technologies may contend for the medium at any given instant. Hence, the support of wireless real-time communications in unmanaged scenarios is a highly challenging task. Wireless low-power technologies have been the focus of a large research effort, for example, in the Wireless Sensor Network domain. Although bringing extended autonomy to battery powered stations, such technologies are known to be negatively influenced by similar technologies contending for the medium and, especially, by technologies using higher power transmissions over the same frequency bands. A frequency band that is becoming increasingly crowded with competing technologies is the 2.4 GHz Industrial, Scientific and Medical band, encompassing, for example, Bluetooth and ZigBee, two lowpower communication standards which are the base of several real-time protocols. Although these technologies employ mechanisms to improve their coexistence, they are still vulnerable to transmissions from uncoordinated stations with similar technologies or to higher power technologies such as Wi- Fi, which hinders the support of wireless dependable real-time communications in open environments. The Wireless Flexible Time-Triggered Protocol (WFTT) is a master/multi-slave protocol that builds on the flexibility and timeliness provided by the FTT paradigm and on the deterministic medium capture and maintenance provided by the bandjacking technique. This dissertation presents the WFTT protocol and argues that it allows supporting wireless real-time communication services with high dependability requirements in open environments where multiple contention-based technologies may dispute the medium access. Besides, it claims that it is feasible to provide flexible and timely wireless communications at the same time in open environments. The WFTT protocol was inspired on the FTT paradigm, from which higher layer services such as, for example, admission control has been ported. After realizing that bandjacking was an effective technique to ensure the medium access and maintenance in open environments crowded with contention-based communication technologies, it was recognized that the mechanism could be used to devise a wireless medium access protocol that could bring the features offered by the FTT paradigm to the wireless domain. The performance of the WFTT protocol is reported in this dissertation with a description of the implemented devices, the test-bed and a discussion of the obtained results.

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D1.S3.4(4). BASES Conference 2015 (Burton-on-Trent), 1-2 December. British Association of Sport and Exercise Sciences

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This paper is concerned with the implementation of a Mobile Broadband System, currently under research in Europe. We present a low-complexity, adaptive transceiver/antenna approach where simple, linear, phased arrays are adjusted under a transmission quality measurement provided by a decision-feedback equalizer. Several simulation results are presented and discussed.

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During the interwar period (1919-1939) protagonists of the early New Zealand Olympic Committee [NZOC] worked to renegotiate and improve the country’s international sporting participation and involvement in the International Olympic Committee [IOC]. To this end, NZOC effectively used its locally based administrators and well-placed expatriates in Britain to variously assert the organisation’s nascent autonomy, independence and political power, progress Antipodean athlete’s causes, and, counter any potential doubt about the nation’s peripheral position in imperial sporting dialogues. Adding to the corpus of scholarship on New Zealand’s ties and tribulations with imperial Britain (in and beyond sport) (e.g. Beilharz and Cox 2007; Belich 2001, 2007; Coombes 2006; MacLean 2010; Phillips 1984, 1987; Ryan 2004, 2005, 2007), in this paper I examine how the political actions and strategic location of three key NZOC agents (specifically, administrator Harry Amos and expatriates Arthur Porritt and Jack Lovelock) worked in their own particular ways to assert the position of the organisation within the global Olympic fraternity. I argue that the efforts of Amos, Porritt and Lovelock also concomitantly served to remind Commonwealth sporting colleagues (namely Britain and Australia) that New Zealand could not be characterised as, or relegated to being, a distal, subdued, or subservient colonial sporting partner. Subsequently I contend that NZOC’s development during the interwar period, and particularly the utility of expatriate agents, can be contextualised against historiographical shifts that encourage us to rethink, reimagine, and rework narratives of empire, colonisation, national identity, commonwealth and belonging.

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Senior thesis written for Oceanography 445

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During the interwar period (1919–1939), protagonists of the early New Zealand Olympic Committee (NZOC) worked to renegotiate and improve the country's international sporting participation and involvement in the International Olympic Committee. To this end, NZOC effectively used its locally based administrators and well-placed expatriates in Britain to variously assert the organization's nascent autonomy, independence and political power, progress Antipodean athlete's causes and counter any potential doubt about the nation's peripheral position in imperial sporting dialogues. Adding to the corpus of scholarship on New Zealand's ties and tribulations with imperial Britain, both in and beyond sport (e.g. Beilharz and Cox, 2007, “Settler Capitalism Revisited,” Thesis Eleven 88: 112–124; Belich, 2001, Paradise Reforged: A History of the New Zealanders from the 1880s to the Year 2000, Auckland: Allen Lane; Belich, 2007, Making Peoples: A History of the New Zealanders from Polynesian Settlement to the End of the Nineteenth Century, Auckland: The Penguin Group; Coombes, 2006, Rethinking Settler Colonialism: History and Memory in Australia, Canada, Aotearoa New Zealand and South Africa, Manchester: Manchester University Press; MacLean, 2010, “New Zealand (Aotearoa),” In Routledge Companion to Sports History, edited by Steve W. Pope and John Nauright, 510–525, London: Routledge; Phillips, 1984, “Rugby, War and the Mythology of the New Zealand Male,” The New Zealand Journal of History 18 (1): 83–103; Phillips, 1987, A Man's Country: The Image of the Pakeha Male, Auckland: Penguin Books; Ryan, 2004, The Making of New Zealand Cricket, 1832–1914, London: Frank Cass; Ryan, 2005, Tackling Rugby Myths: Rugby and New Zealand Society 1854–2004, Dunedin: University of Otago Press; Ryan, 2007, “Sport in 19th-Century Aotearoa/New Zealand: Opportunities and Constraints,” In Sport in Aotearoa/New Zealand Society, edited by Chris Collins and Steve Jackson, 96–111, Auckland: Thomson), I will examine how the political actions and strategic location of three key NZOC agents (specifically, administrator Harry Amos and expatriates Arthur Porritt and Jack Lovelock) worked in their own particular ways to assert the position of the organization within the global Olympic fraternity. I argue that the efforts of Amos, Porritt and Lovelock also concomitantly served to remind Commonwealth sporting colleagues (namely Britain and Australia) that New Zealand could not be characterized as, or relegated to being, a distal, subdued or subservient colonial sporting partner. Subsequently, I contend that NZOC's development during the interwar period, and particularly the utility of expatriate agents, can be contextualized against historiographical shifts that encourage us to rethink, reimagine and rework narratives of empire, colonization, national identity, commonwealth and belonging.

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Data registration refers to a series of techniques for matching or bringing similar objects or datasets together into alignment. These techniques enjoy widespread use in a diverse variety of applications, such as video coding, tracking, object and face detection and recognition, surveillance and satellite imaging, medical image analysis and structure from motion. Registration methods are as numerous as their manifold uses, from pixel level and block or feature based methods to Fourier domain methods. This book is focused on providing algorithms and image and video techniques for registration and quality performance metrics. The authors provide various assessment metrics for measuring registration quality alongside analyses of registration techniques, introducing and explaining both familiar and state–of–the–art registration methodologies used in a variety of targeted applications.