174 research outputs found
Spectrum avaílability assessment tool for TV white space
The growth of wireless communication relies on the availability of radio frequency for new services. More efficient spectrum allocations are required to serve the increasing data per user. The major regulatory bodies are formulating new spectrum management techniques to forge the growing spectrum scarcity. Exclusive use of spectrum is proved to be inefficient in many spectrum occupancy measurement campaigns. As a result, spectrum sharing methods are being considered.
TV broadcasting is not using the allocated frequency in some geographic areas, creating coverage holes known as TV white spaces. Both the industry and the regulators are investigating the capability of TVWS, as a potential source of spectrum for emerging wireless services. The FCC, in the US, has already released the requirements for opportunistic access to the TV whites paces. In a similar fashion, ECC, the pan-European regulator is finalizing the work on the technical and operational requirements for the possible use of cognitive radio in this spectrum.
In this thesis work, an integrated web-based spectrum availability assessment tool is developed for Finland. The tool is a front-end visualization of a time intensive computational process to answer key technical questions related to TVWS - what secondary data rate can be supported in the available white space spectrum? The assessment involves estimation of the available TVWS and its capacity for cellular-type secondary systems. The relative effects of the secondary system parameters on the TV system are compared using appropriate signal to noise and interference ratio plots. The tool uses dynamic web technologies for a seamless and user-friendly visualization of the assessment
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The development of the terrestrial broadcasting networks of the United Kingdom in the twentieth century
This thesis describes an investigation into the evolution of terrestrial broadcasting -a vital new medium that has had an enormous social impact. The approach has been to concentrate upon the research and development needed to plan the intricate radio and television transmitter networks. These processes required national and international agreement on the use of the radio frequency spectrum, and the specification of many hundreds of transmitting stations. They provided the link between the broadcasters and the public, and this work presents a unique illustration of a project which dealt with many novel technical problems whilst accommodating the demands of all those concerned with the exploitation of the medium.
The UK became prominent in the field of broadcasting technology, particularly in areas concerned with propagation and service planning. The geographical position of this country between large land and sea masses, the nature of its terrain, meteorology and its population distribution, presented a wide range of distinctive problems. Research in the UK provided valuable evidence for the subsequent planning of services throughout the world, although during the rapid development of broadcasting it was impossible to examine fully all the experimental results which were produced. With resources not previously available, the author - engaged on planning work since the middle of the century - has researched evidence much of which was archived many years ago. It is not simply a work of historical interest, because new information concerning radio propagation has emerged. Its timing is also appropriate, because the beginning of the twenty-first century is witnessing revolutionary changes in broadcasting
Satellite Communications
This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking
Cyber Security
This open access book constitutes the refereed proceedings of the 16th International Annual Conference on Cyber Security, CNCERT 2020, held in Beijing, China, in August 2020. The 17 papers presented were carefully reviewed and selected from 58 submissions. The papers are organized according to the following topical sections: access control; cryptography; denial-of-service attacks; hardware security implementation; intrusion/anomaly detection and malware mitigation; social network security and privacy; systems security
Towards a new cloud-based planning and optimization methodology for mobile communication networks
The great concern of telecommunication operators to offer high-quality services
to their customers requires a constant care with the state of the networks. These
networks can present some problems that imply that the experience offered to customers is unsatisfactory. In order to monitor these situations, operators collect, on
a fairly regular basis, data, like drive tests, that allow them to monitor and correct
minor issues. This thesis takes advantage of the data collected and uses it in network planning in order to precisely obtain the coverage estimation of a network. In
order to automate failure correction mechanisms, a totally automatic propagation
model is presented, which precisely describes the state of the network, allowing it
to be used for network planning and optimisation. After its implementation, the
model was compared to a second model, generated through Artificial Intelligence,
which is completely agnostic to all telecommunications knowledge. These models,
for the considered scenarios, reached average absolute errors between estimated
and actual values of 6.1 dB with a standard deviation of 4 dB.
The existence of several real telecommunication network measures and their
evolution to Multiple Input, Multiple Output (MIMO) systems motivated not only
the investigation on the coverage impact with the change from a Single Input, Single Output (SISO) to a MIMO system, but also the investigation on the reduction
of complexity of the receivers used in MIMO systems. The closer the Bit Error
Rate performance of the receiver is to the Matched Filter Bound, the smaller will
be the reduction in the coverage area with the transition from a SISO system to
a MIMO system.A grande preocupação dos operadores de telecomunicações em oferecerem serviços de alta qualidade aos seus clientes leva a um constante cuidado com o estado das redes. Estas redes podem apresentar alguns problemas que implicam que a
experiência oferecida aos clientes seja desagradável. De forma a monitorizar estas situações, os operadores recolhem, com bastante regularidade, dados, como "drive tests", que lhes permitem avaliar e corrigir pequenos problemas. Esta tese aproveita
os dados recolhidos e utiliza-os no planeamento da rede de forma a obter fielmente a estimativa de cobertura de uma rede. De forma a automatizar mecanismos de correção de falhas, é apresentado um modelo de propagação completamente automático, que descreve de forma precisa o estado da rede permitindo que seja aplicado em algoritmos de planeamento e otimização da rede. Após a sua implementação, este modelo foi comparado com um segundo modelo, gerado através de inteligência artificial, que é completamente agnóstico a todo o conhecimento de telecomunicações. Estes modelos, para os cenários estudados, atingiram erros absolutos médios entre os valores estimados e os valores reais de 6.1 dB com um desvio padrão de 4 dB.
A existência de diversos dados reais das redes de telecomunicações e a evolução para os sistemas "Multiple Input", "Multiple Output" (MIMO) motivou não só a investigação no impacto da cobertura com a mudança de um sistema "Single Input",
"Single Output" (SISO) para um sistema MIMO, mas também a investigação na redução de complexidade dos recetores utilizados em sistemas MIMO. Quanto mais próxima a "Bit Error Rate performance" do recetor estiver do "Matched Filter Bound",
menor será a redução na área de cobertura com a transição de um sistema SISO para um sistema MIMO
Contribution to quality of user experience provision over wireless networks
The widespread expansion of wireless networks has brought new attractive possibilities to end users. In addition to the mobility capabilities provided by unwired devices, it is worth remarking the easy configuration process that a user has to follow to gain connectivity through a wireless network. Furthermore, the increasing bandwidth provided by the IEEE 802.11 family has made possible accessing to high-demanding services such as multimedia communications. Multimedia traffic has unique characteristics that make it greatly vulnerable against network impairments, such as packet losses, delay, or jitter. Voice over IP (VoIP) communications, video-conference, video-streaming, etc., are examples of these high-demanding services that need to meet very strict requirements in order to be served with acceptable levels of quality. Accomplishing these tough requirements will become extremely important during the next years, taking into account that consumer video traffic will be the predominant traffic in the Internet during the next years. In wired systems, these requirements are achieved by using Quality of Service (QoS) techniques, such as Differentiated Services (DiffServ), traffic engineering, etc. However, employing these methodologies in wireless networks is not that simple as many other factors impact on the quality of the provided service, e.g., fading, interferences, etc. Focusing on the IEEE 802.11g standard, which is the most extended technology for Wireless Local Area Networks (WLANs), it defines two different architecture schemes. On one hand, the infrastructure mode consists of a central point, which manages the network, assuming network controlling tasks such as IP assignment, routing, accessing security, etc. The rest of the nodes composing the network act as hosts, i.e., they send and receive traffic through the central point. On the other hand, the IEEE 802.11 ad-hoc configuration mode is less extended than the infrastructure one. Under this scheme, there is not a central point in the network, but all the nodes composing the network assume both host and router roles, which permits the quick deployment of a network without a pre-existent infrastructure. This type of networks, so called Mobile Ad-hoc NETworks (MANETs), presents interesting characteristics for situations when the fast deployment of a communication system is needed, e.g., tactics networks, disaster events, or temporary networks. The benefits provided by MANETs are varied, including high mobility possibilities provided to the nodes, network coverage extension, or network reliability avoiding single points of failure. The dynamic nature of these networks makes the nodes to react to topology changes as fast as possible. Moreover, as aforementioned, the transmission of multimedia traffic entails real-time constraints, necessary to provide these services with acceptable levels of quality. For those reasons, efficient routing protocols are needed, capable of providing enough reliability to the network and with the minimum impact to the quality of the service flowing through the nodes. Regarding quality measurements, the current trend is estimating what the end user actually perceives when consuming the service. This paradigm is called Quality of user Experience (QoE) and differs from the traditional Quality of Service (QoS) approach in the human perspective given to quality estimations. In order to measure the subjective opinion that a user has about a given service, different approaches can be taken. The most accurate methodology is performing subjective tests in which a panel of human testers rates the quality of the service under evaluation. This approach returns a quality score, so-called Mean Opinion Score (MOS), for the considered service in a scale 1 - 5. This methodology presents several drawbacks such as its high expenses and the impossibility of performing tests at real time. For those reasons, several mathematical models have been presented in order to provide an estimation of the QoE (MOS) reached by different multimedia services In this thesis, the focus is on evaluating and understanding the multimedia-content transmission-process in wireless networks from a QoE perspective. To this end, firstly, the QoE paradigm is explored aiming at understanding how to evaluate the quality of a given multimedia service. Then, the influence of the impairments introduced by the wireless transmission channel on the multimedia communications is analyzed. Besides, the functioning of different WLAN schemes in order to test their suitability to support highly demanding traffic such as the multimedia transmission is evaluated. Finally, as the main contribution of this thesis, new mechanisms or strategies to improve the quality of multimedia services distributed over IEEE 802.11 networks are presented. Concretely, the distribution of multimedia services over ad-hoc networks is deeply studied. Thus, a novel opportunistic routing protocol, so-called JOKER (auto-adJustable Opportunistic acK/timEr-based Routing) is presented. This proposal permits better support to multimedia services while reducing the energy consumption in comparison with the standard ad-hoc routing protocols.Universidad Politécnica de CartagenaPrograma Oficial de Doctorado en Tecnologías de la Información y Comunicacione
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