Implementação de sistemas de telecomunicações utilizando dispositivos lógicos programáveis

Mestradom em Engenharia Electrónica e TelecomunicaçõesA utilização de dispositivos lógicos programáveis, especialmente FPGA’s e CPLD’s, é cada vez mais comum. Estes dispositivos podem mesmo vir a ter um impacto semelhante ao provocado pelo microprocessador. Os sistemas de telecomunicações são dos que mais têm a ganhar com a utilização de lógica programável. O tema principal desta dissertação consistiu em criar uma plataforma que facilite a simulação, desenvolvimento e teste de sistemas de rádio digital, tirando partido da versatilidade oferecida pelos dispositivos lógicos programáveis. Para tal foi montada uma placa com um destes dispositivos, desenvolvido software de comunicação entre a placa e um PC e implementados alguns dos algoritmos essenciais utilizando a linguagem VHDL. Após uma introdução aos conceitos básicos relacionados com os sistemas de rádio digital é apresentada uma descrição desta plataforma e do trabalho que foi realizado no âmbito desta dissertação.The use of programmable logic devices, especially FPGA’s and CPLD’s, is becoming very common. This devices can have in the future an impact as important as the microprocessor had in the past. Telecommunication systems can have great advantages by the use of programmable logic devices. The main subject of this thesis is the creation of a platform that allows the simulation, development, and testing of digital radio systems, taking advantage of the versatility of programmable logic devices. A board was built with a programmable device, software was written for the communication between the board and an PC, and some essencial algorithms were implemented using VHDL. After an introduction to the basic concepts of digital radio, we give a description of this platform and the work performed for this thesis

A soil classification for seismic hazard assessment and mitigation of the Algarve

The Algarve province of Portugal is located near the E-W Eurasia-Africa plate boundary. It is characterized by a moderate seismicity, with some important historical earthquakes causing important damage and economical losses. Not only has it suffered the effects of large plate boundary events but also the impact of local onshore moderate-sized earthquake sources. The seismic hazard evaluation and mitigation of the area is therefore of great importance to the local populations and the large number of tourists that frequent the region. This paper focuses the evaluation of the most interesting and useful geotechnical near-surface parameters and a soil classification. The classification based upon the European Code 8 for civil engineering and SPT bedrock data, was carried out for land use planning and design of critical facilities. P-wave and S-wave seismic velocities were obtained through the acquisition, processing and interpretation refraction profiles. Hundreds of SPT parameters from available boreholes drilled for engineering and water supply were used and subsoil classification based on geophysical and geotechnical parameters is presented. Other parameters, such as Vp/Vs ratios and the Poisson coefficient were estimated and were computed to provide information for future site effect studies. The experimental procedure tested here is relatively fast, economical and easy to perform and can be useful to estimate soil microzoning and seismic hazard mapping in the absence of local earthquake records

Characterization of an Intraplate Seismogenic Zone Using Geophysical and Borehole Data: The Vila Franca de Xira Fault, Portugal

The Vila Franca de Xira (VFX) fault is a regional fault zone located about 25 km northeastof Lisbon, affecting Neogene sediments. Recent shear-wave seismic studies show thatthis complex fault zone is buried beneath Holocene sediments and is deforming thealluvial cover, in agreement with a previous work that proposes the fault as the sourceof the 1531 Lower Tagus Valley earthquake. In this work, we corroborate these resultsusingS-wave,P-wave, geoelectric, ground-penetrating radar and borehole data, con-firming that the sediments deformed by several fault branches are of Upper Pleistoceneto Holocene. Accumulated fault vertical offsets of about 3 m are estimated from theintegrated interpretation of geophysical and borehole data, including 2D elastic seismicmodeling, with an estimated resolution of about 0.5 m. The deformations affecting theTagus alluvial sediments probably resulted from surface or near-surface rupture of theVFX fault during M∼7 earthquakes, reinforcing the fault as the seismogenic source ofregional historical events, as in 1531, and highlighting the need for preparedness for thenext even

Earthquake mitigation in the Lisbon and Lower Tagus Valley area, Portugal

Diapositivos apresentados durante o Thirteenth International Congress of the Brazilian Geophysical Society

High-resolution P- and S-wave reflection studies of an intraplate structure: The Azambuja fault, Portugal

The Azambuja fault is a NNE trending structure located 50 km north of Lisbon, the capital and most populous city of Portugal. The fault has been considered as a possible source for the historical, large earthquakes. Understanding this fault is a priority in seismic hazard evaluation of this region. The fault has a clear morphological signature. Miocene and Pliocene sediments are tilted eastward and cut by steeply dipping mesoscale fault segments, presenting reverse and normal offsets with a net downthrow to the east. Neotectonic studies indicate a Quaternary slip on the fault of 0.05–0.06 mm/year. However, no direct evidence of the Azambuja fault affecting the Pleistocene or Holocene sediments was found so far. Here, we present the findings from high-resolution seismic reflection studies using both P- and S-waves over the Holocene deposits. The detection of small-throw faulting in ductile sediments is a challenging task. We show that multiple signatures, like perturbations in the reflection hyperbolae visible in shot and CMP gathers, interruptions of reflectors in stacked sections, lateral seismic velocity variations obtained by horizon velocity analysis, all at coincident locations, strongly suggest that the activity of the Azambuja fault has affected the Holocene sediments in the study area. The lateral velocity variations are corroborated by wavepath eikonal traveltime tomography and velocity analysis supported by seismic modeling. By means of 2D viscoelastic modeling, we explain the absence of fault-related diffractions and negligible back-scattered energy from the fault. Using data from nearby boreholes, we find that the 15 ka old alluvium cover has indeed been disturbed by the presence of shallow fault strands. Considering the estimated vertical throws and the empirical relationships between fault length, co-seismic rupture and magnitude, a slip rate of 0.07 mm/y, slightly larger than previously thought, is expected for this fault.</p

Estudo Geofísico e Geológico da Falha de Vila Franca de Xira

A região de Lisboa e Vale Inferior do Tejo foi afetada por vários sismos destrutivos que provocaram grandes prejuízos materiais e perdas de vida. As fontes geradoras desses sismos históricos situam-se quer na zona de fronteira de placas Ibéria-África, localizada cerca de 300 km a sul, quer no interior da própria região. Neste artigo, estuda-se uma falha geológica local, a falha de Vila Franca de Xira, que se julga ter ocasionado o terramoto de Lisboa de 1531. Apesar da ausência de evidência geológica direta para a presença duma rotura superficial da falha, demonstra-se através da utilização de métodos geofísicos que se trata de uma zona de falha ativa, sendo possivelmente a fonte de geração daquele sismo