247 research outputs found
Probing the Interstellar Medium Toward Timing Array Millisecond Pulsars with the Murchison Widefield Array
Millisecond pulsars are highly sought-after targets for timing-array experiments that aim to detect ultra-low frequency gravitational waves. However, there are multiple challenges before this goal can be achieved. Interstellar medium effects on pulsar signals are amongst them. The magnitudes of these effects are much stronger at longer radio wavelengths, therefore low-frequency observations with the Murchison Widefield Array are especially promising for the related studies. This thesis presents such a study for two millisecond pulsars
A Multi-Frequency Investigation of Air-To-Ground Urban Propagation Using a GPU-based Ray Launching Algorithm
Unmanned Aerial Vehicles (UAV), also known as “drones”, are attracting increasing attention as enablers for many technical applications and services, and this trend is likely to continue in the next future. When compared to conventional terrestrial communications, those making use of UAVs as base- or relay-stations can definitely be more useful and flexible in reaction to specific events, like natural disasters and terrorist attacks. Among the many and different fields, UAV enabled communications emerge as one of the most promising solutions for next-generation mobile networks, with a special focus on the extension of coverage and capacity of mobile radio networks. Motivated by the air-to-ground (A2G) propagation conditions which are likely to be different than those experienced by traditional ground communication systems, this paper aims at investigating the narrowband properties of the air-to-ground channel for 5G communications and beyond by means of GPU accelerated ray launching simulations. Line of sight probability as well as path loss exponent and shadowing standard deviations are analysed for different UAV flight levels, frequencies and dense urban scenarios, and for different types of on board antennas. Thanks to the flexibility of the ray approach, the role played by the different electromagnetic interactions, namely reflection, diffraction and diffuse scattering, in the air-to-ground propagation process is also investigated. Computation time is reported as well to show that designing UAV communication networks and optimising their performances in a fast and reliable manner, might avoid exhausting – multiple - measurement campaigns
Modelling of radio wave propagation using Finite Element Analysis.
Fourth generation (4G) wireless communication systems are intended to support high data rates which requires careful and accurate modelling of the radio environment. In this thesis, for the first time finite clement based accurate and computationally efficient models of wave propagation in different outdoor and indoor environments has been developed. Three different environments were considered: the troposphere, vegetation and tunnels and wave propagation in these environments were modelled using finite element analysis. Use of finite elements in wave propagation modelling is a novel idea although many propagation models and approaches were used in past.
Coverage diagrams, path loss contours and power levels were calculated using developed models in the troposphere, vegetation and tunnels. Results obtained were compared with commercially available software Advanced Refractive Effects Prediction Software (AREPS) to validate the accuracy of the developed approach and it is shown that results were accurate with an accuracy of 3dB. The developed models were very flexible in handling complex geometries and similar analysis can be easily extended to other environments. A fully vectored finite element base propagation model was developed for straight and curved tunnels. An optimum range of values of different electrical parameters for tunnels of different shapes has been derived.
The thesis delivered a novel approach to modelling radio channels that provided a fast and accurate solution of radio wave propagation in realistic environments. The results of this thesis will have a great impact in modelling and characterisation of future wireless communication systems
Calibration Instrumentation for the Hydrogen Intensity and Real-Time Analysis eXperiment
The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a 21 cm neutral hydrogen intensity mapping experiment to be deployed in the Karoo Desert in South Africa. It aims to improve constraints on the dark energy equation of state through measurements of large-scale structure at high redshift, while doubling as a state-of-the-art fast radio burst (FRB) detector. This dissertation focuses on two aspects of the HIRAX instrument characterization: (1) optimizing the signal-to-noise of antennas, through the design and implementation of a custom test-bed for determining the noise temperature of radio antennas operating between 400-800MHz, and (2) mapping the HIRAX telescope beam pattern with a custom drone calibration system. The work described is critical to HIRAX\u27s development, both by informing final antenna design and providing the tools to generate beam maps that will factor into all cosmological analysis
Theoretical and experimental contributions for modeling wireless channels
Trabalho de Conclusão de Curso (graduação)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2017.Este trabalho de conclusão de curso visa agregar contribuições teóricas e experimentais
para a modelagem de redes sem fio à partir de quatro projetos realizados durante um
estágio supervisionado entre a Universidade de Brasília e a escola francesa de engenharia
ENSEIRB-MATMECA durante o ano de 2017. Todos os projetos desse trabalho giram
em torno do tema "desafios atuais nas comunicações sem fio" e tem como objetivo a
apresentação de tais desafios através de uma breve introdução teórica seguida da realização
de simulações, análises estatísticas ou medições em campo. O primeiro projeto propõem
um estudo teórico e a validação experimental da distribuição de desvanecimento α-μ/Γ
generalizada, usada nesse trabalho para caracterizar ambientes realistas que experimentam
desvanecimento composto. Ainda no escopo de análises estatísticas, o segundo projeto
propõe uma caracterização da qualidade do sinal celular à partir de dados de potência
medidos usando um aplicativo Android de analise de qualidade de redes móveis. As análises
estatísticas realizadas poderão auxiliar operadoras de telefonia móvel à parametrizar suas
redes e contribuir para o melhoramento da cobertura celular no pais. Em seguida, o
terceiro projeto desenvolvido nesse trabalho de conclusão de curso propõe estudos práticos
e teóricos de interferência entre os sistema LTE 700MHz e TV digital em Brasília na região
da Asa Norte, um tema recente de grande importância dada a desconexão da TV analógica
no Brasil até 2018. Por fim, o quarto projeto, realizado em parceria com a Agência
Nacional de Telecomunicações (ANATEL) propõe contribuições para o desenvolvimento
de um simulador de rede IMT para uso em estudos de compartilhamento e compatibilidade
proposto para ajudar na identificação de novas faixas de frequência para o IMT-2020. Os
projetos propostos nesse trabalho focam na caracterização e modelagem de canais sem fio à
partir do levantamento de estatísticas de primeira ordem, na análise de qualidade das redes
celulares no país com base nas informações sobre a cobertura celular experimentada pelos
usuários de telefonia móvel e na análise da interferência entre sistemas à partir de estudos
entre o LTE e a TV digital e da busca de novas possíveis frequências para o 5G. A realização
do estágio supervisionado e desse trabalho de conclusão de curso é um requerimento oficial
para a obtenção do título de "Engenheiro diplomado do Instituto politécnico de Bordeaux,
especialidade Engenharia eletrônica" pela ENSEIRB-MATMECA e para a obtenção do
titulo de "Engenheiro de redes de comunicação" pela Universidade de Brasília.This final course assignment aims to add theoretical and experimental contributions to the
modeling of wireless networks from four different projects carried out over an supervised
internship held between the University of Brasília and the french school of engineering
ENSEIRB-MATMECA during the year of 2017. All projects revolve around the central
theme "current challenges in wireless communications" and aims to present such challenges
through a brief theoretical introduction followed by simulations, statistical analyzes or
field measurements. The first project proposes a theoretical study and the experimental
investigation of the α-μ/Γ generalized fading distribution, used in this work to characterize
realistic environments that experience composite fading. A second project, also based on
statistical analysis, proposes a characterization of the mobile phone signal quality from
power data measured using an Android application of mobile network quality analysis.
Statistical analyzes can help mobile operators to parameterize their network and contribute
to the improvement of cellular coverage in the country. Next, the third project developed
in the internship proposes practical and theoretical studies of interference between the LTE
700MHz system and digital TV in Brasília in the region of Asa Norte, a recent topic of
great importance given the analogue TV disconnection in Brazil until 2018. Finally, the
fourth project, carried out in partnership with the National Telecommunications Agency
(ANATEL), proposes contributions for the development of an IMT network simulator for
use in sharing and compatibility studies to help in the identification of new frequency bands
for the IMT-2020. The projects proposed in this work focus on the characterization and
modeling of wireless channels from first order statistics, on the analysis of the quality of
cellular networks in the country based on the information collected from the App about
the network coverage experienced by final users and on the analysis of interference between
systems based on studies between LTE and digital TV and on the search for new possible
frequencies for 5G. The realization of the supervised internship was an official requirement to
obtain the title of "Licensed Engineer of the Polytechnic Institute of Bordeaux, specialized
in Electronic Engineering" by ENSEIRB-MATMECA and to obtain the title of "Network
Communications Engineer" by the University of Brasília
A Technical and Market study for WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is a broadband wireless technology based on IEEE 802.16-2004 and IEEE 802.16e-2005. This thesis is a study of WiMAX technology and market. The background of WiMAX development is introduced and opportunities and challenges for WiMAX are analyzed in the beginning. Then the thesis focuses on an overview of WiMAX technology, which addresses the physical layer, MAC layer and WiMAX network architecture. The deployment status is investigated in the fourth chapter. Both product development situation and market status are discussed in this section. In the last chapter, the future development trend of WiMAX is addressed
Accurate and efficient full-wave modelling for indoor radio wave propagation
The transition towards next-generation communication technologies has increased the need for accurate knowledge about the wireless channel. Knowledge of radio wave propagation is vital to the continued development of efficient wireless communications systems capable of providing a high data throughput and reliable connection. Thus, there is an increased need for accurate propagation models that can rapidly predict and describe the propagation channel. This is extremely challenging for indoor environments given the large variety of materials encountered and very complex and widely varying geometries.Currently, empirical or ray optical models are the most common for indoor propagation. Empirical models based on measurement campaigns provide limited accuracy, are very costly and time-consuming but provide rapid predictions. Deterministic models are applied to the geometrical representation of the environment and are based on Maxwell’s equations. They can produce more accurate predictions than empirical models. Ray tracing, an approximate model, is the most popular deterministic model for indoor propagation. The current trend of research is focused on improving its accuracy. Full-wave propagation models are based on the numerical solution of Maxwell’s equations. They are able to produce accurate predictions about the wireless channel. However, they are very computationally expensive. Thus, there has been limited attempts at developing indoor propagation models based on full-wave techniques. In this work, the Volume Electric Field Integral Equation (VEFIE) is used as the basis of a full-wave indoor propagation model. The 2D and 3D formulations of the VEFIE are applied to model the propagation of radio waves indoors. An enhancement to the 2D VEFIE, called 2D to 3D models, is developed to improve its accuracy and utilise its efficiency. It is primarily used for the prediction of time domain characteristics due to its high efficiency whereas the 3D VEFIE is shown to be suitable for frequency domain predictions
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