SAR imaging of buried objects from MoM modelled scattered field

Synthetic aperture radar (SAR) images of resonant buried objects are modelled in the presence of ground surface clutter. The method of moments (MoM) is used to model scattered fields from a resonant buried conductor and clutter is modelled as a bivariant Gaussian distribution. A diffraction stack SAR imaging technique is applied to the ultra-wideband waveforms to give a bipolar signal image. A number of examples have been computed to illustrate the combined effects of SAR processing with resonant targets and clutter. SAR images of different targets show differences which may facilitate target identification. To maximise the peak signal-to-clutter ratio, an image correlation technique is applied and the results are shown.

Microstructural evolution of the Serido Belt, NE-Brazil: the effect of two tectonic events on development of c-axis preferred orientation in quartz

The polyphase evolution of the Serido Belt (NE-Brazil) includes D, crust formation at 2.3-2.1 Ga, D-2 thrust tectonics at 1.9 Ga and crustal reworking by D-3 strike-slip shear zones at 600 Ma. Microstructural investigations within mylonites associated with D-2 and D-3 events were used to constrain the tectono-thermal evolution of the belt. D-2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions (600-650 degreesC) through grain boundary migration, subgrain rotation and operation of quartz Q-prism slip. Continued shearing and exhumation of the terrain forced the re-equilibration of high-T fabrics and the switching of slip systems from (c)-prism to positive and negative (a)-rhombs. During D-3, enhancement of ductility by dissipation of heat that came from syn-D-3 granites developed wide belts of amphibolite facies mylonites. Continued shearing, uplift and cooling of the region induced D-3 shear zones to act in ductile-brittle regimes, marked by fracturing and development of thinner belts of greenschist facies mylonites. During this event, switching from (a)-prism to a basal slip indicates a thermal path from 600 to 350 degreesC. Therefore, microstructures and quartz c-axis fabrics in polydeformed rocks from the Serido Belt preserve the record of two major events, which includes contrasting deformation mechanisms and thermal paths. (C) 2003 Elsevier Ltd. All rights reserved.

Distribuição de sinais rádio e vídeo sobre fibra

As comunicações ópticas e as comunicações sem fios têm sofrido uma grande evolução ao longo das últimas décadas. Com o objectivo de juntar as vantagens de cada um dos sistemas surgiu o que se designa por rádio sobre fibra. Este sistema permite centralizar todo o processamento necessário num só local, na estação central, simplificando assim a estação base. Esta simplificação permite reduzir os custos de implementação e torna o sistema menos complexo. Esta dissertação de mestrado tem como objectivo principal estudar e simular um sistema que permite o envio de sinais vídeo e rádio pela fibra óptica para posterior difusão, utilizando o conceito de rádio sobre fibra. Os sinais enviados foram o LTE (Long Term Evolution), o UWB (Ultra WideBand) e o WiMAX (Worldwide Interoperability for Microwave Access). O primeiro disponibiliza o serviço de voz, o segundo disponibiliza o serviço de televisão e o último dá suporte à internet. Estes sinais foram modulados em OFDM (Orthogonal Frequency Division Multiplex), porque, posteriormente, estes sinais vão ser difundidos num ambiente sem fios e este tipo de modulação minimiza o efeito de multipercurso e da interferência intersimbólica. Com este estudo pretende-se verificar qual a viabilidade de um sistema que permite o envio de três sinais distintos simultaneamente (serviço Triple Play). Ao analisar os resultados deste sistema concluiu-se que a sua aplicabilidade pode apresentar algumas limitações, dependendo do tipo de modulação e do tipo de modulador que se utilize. Os moduladores ópticos utilizados foram o MZ (Mach-Zehnder) e o EA (Electro-Absorption). A qualidade do sinal recebido foi analisada com base no valor de EVM (Error Vector Magnitude). O primeiro modulador foi aquele que apresentou mais limitações, pois o desempenho do sistema é comprometido para distâncias superiores a 40 km e para potências de entrada inferiores a 0 dBm. Este tipo de sistema apresenta um EVM mais baixo quando a potência de entrada utilizada está entre 0 e 6 dBm. Se o modulador utilizado for o EA, o sistema apresenta um EVM mais baixo quando se utiliza um índice de modulação entre 20% e 30%, para uma potência de entrada entre 0 e 2 dBm.

Análise do impacto da utilização de femto-células em LTE

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia de Electrónica e Telecomunicações

Interference detection in GNSS signals using Gaussianity criterion

We assess the performance of Gaussianity tests, namely the Anscombe-Glynn, Lilliefors, Cramér-von Mises, and Giannakis-Tsatsanis (G-T), with the purpose of detecting narrowband and wideband interference in GNSS signals. Simulations have shown that the G-T test outperforms the others being suitable as a benchmark for comparison with different types of interference detection algorithms. © 2014 EURASIP.

Sistema de transmissão rádio UWB para amplificação digital de áudio com modulação sigma-delta

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Electrotécnica e de Computadores

Low power low voltage quadrature RC oscillators for modern RF receivers

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Electrotécnica e de Computadores

Characterisation of noisy speech channels in 2G and 3G mobile networks

As the wireless cellular market reaches competitive levels never seen before, network operators need to focus on maintaining Quality of Service (QoS) a main priority if they wish to attract new subscribers while keeping existing customers satisfied. Speech Quality as perceived by the end user is one major example of a characteristic in constant need of maintenance and improvement. It is in this topic that this Master Thesis project fits in. Making use of an intrusive method of speech quality evaluation, as a means to further study and characterize the performance of speech codecs in second-generation (2G) and third-generation (3G) technologies. Trying to find further correlation between codecs with similar bit rates, along with the exploration of certain transmission parameters which may aid in the assessment of speech quality. Due to some limitations concerning the audio analyzer equipment that was to be employed, a different system for recording the test samples was sought out. Although the new designed system is not standard, after extensive testing and optimization of the system's parameters, final results were found reliable and satisfactory. Tests include a set of high and low bit rate codecs for both 2G and 3G, where values were compared and analysed, leading to the outcome that 3G speech codecs perform better, under the approximately same conditions, when compared with 2G. Reinforcing the idea that 3G is, with no doubt, the best choice if the costumer looks for the best possible listening speech quality. Regarding the transmission parameters chosen for the experiment, the Receiver Quality (RxQual) and Received Energy per Chip to the Power Density Ratio (Ec/N0), these were subject to speech quality correlation tests. Final results of RxQual were compared to those of prior studies from different researchers and, are considered to be of important relevance. Leading to the confirmation of RxQual as a reliable indicator of speech quality. As for Ec/N0, it is not possible to state it as a speech quality indicator however, it shows clear thresholds for which the MOS values decrease significantly. The studied transmission parameters show that they can be used not only for network management purposes but, at the same time, give an expected idea to the communications engineer (or technician) of the end-to-end speech quality consequences. With the conclusion of the work new ideas for future studies come to mind. Considering that the fourth-generation (4G) cellular technologies are now beginning to take an important place in the global market, as the first all-IP network structure, it seems of great relevance that 4G speech quality should be subject of evaluation. Comparing it to 3G, not only in narrowband but also adding wideband scenarios with the most recent standard objective method of speech quality assessment, POLQA. Also, new data found on Ec/N0 tests, justifies further research studies with the intention of validating the assumptions made in this work.

CANDi: context-aware node discovery for short-range cooperation

Multi-standard mobile devices are allowing users to enjoy higher data rates with ubiquitous connectivity. However, the benefits gained from multiple interfaces come at an expense—that being higher energy consumption in an era where mobile devices need to be energy compliant. One promising solution is the usage of short-range cooperative communication as an overlay for infrastructure-based networks taking advantage of its context information. However, the node discovery mechanism, which is pivotal to the bearer establishment process, still represents a major burden in terms of the total energy budget. In this paper, we propose a technology agnostic approach towards enhancing the MAC energy ratings by presenting a context-aware node discovery (CANDi) algorithm, which provides a priori knowledge towards the node discovery mechanism by allowing it to search nodes in the near vicinity at the ‘right time and at the right place’. We describe the different beacons required for establishing the cooperation, as well as the context information required, including battery level, modes, location and so on. CANDi uses the long-range network (WiMAX and WiFi) to distribute the context information about cooperative clusters (Ultra-wideband-based) in the vicinity. The searching nodes can use this context in locating the cooperative clusters/nodes, which facilitates the establishing of short-range connections. Analytical and simulation results are obtained, and the energy saving gains are further demonstrated in the laboratory using a customised testbed. CANDi saves up to 50% energy during the node discovery process, while the demonstrative testbed shows up to 75% savings in the total energy budget, thus validating the algorithm, as well as providing viable evidence to support the usage of short-range cooperative communications for energy savings.

SIR performance evaluation of MB-OFDM UWB system with residual timing offset

Signal-to-interference ratio (SIR) performance of a multiband orthogonal frequency division multiplexing ultra-wideband system with residual timing offset is investigated. To do so, an exact mathematical derivation of the SIR of this system is derived. It becomes obvious that, unlike a cyclic prefixing based system, a zero padding based system is sensitive to residual timing offset.

Distributed Linear Precoding and User Selection in Coordinated Multicell Systems

In this manuscript we tackle the problem of semidistributed user selection with distributed linear precoding for sum rate maximization in multiuser multicell systems. A set of adjacent base stations (BS) form a cluster in order to perform coordinated transmission to cell-edge users, and coordination is carried out through a central processing unit (CU). However, the message exchange between BSs and the CU is limited to scheduling control signaling and no user data or channel state information (CSI) exchange is allowed. In the considered multicell coordinated approach, each BS has its own set of cell-edge users and transmits only to one intended user while interference to non-intended users at other BSs is suppressed by signal steering (precoding). We use two distributed linear precoding schemes, Distributed Zero Forcing (DZF) and Distributed Virtual Signalto-Interference-plus-Noise Ratio (DVSINR). Considering multiple users per cell and the backhaul limitations, the BSs rely on local CSI to solve the user selection problem. First we investigate how the signal-to-noise-ratio (SNR) regime and the number of antennas at the BSs impact the effective channel gain (the magnitude of the channels after precoding) and its relationship with multiuser diversity. Considering that user selection must be based on the type of implemented precoding, we develop metrics of compatibility (estimations of the effective channel gains) that can be computed from local CSI at each BS and reported to the CU for scheduling decisions. Based on such metrics, we design user selection algorithms that can find a set of users that potentially maximizes the sum rate. Numerical results show the effectiveness of the proposed metrics and algorithms for different configurations of users and antennas at the base stations.

Microwave imaging of the axilla to aid breast cancer diagnosis

Breast cancer is the most common type of cancer among women all over the world. An important issue that is not commonly addressed in breast cancer imaging literature is the importance of imaging the underarm region—where up to 80% of breast cancer cells can metastasise to. The first axillary lymph nodes to receive drainage from the primary tumour in the breast are called Sentinel Node. If cancer cells are found in the Sentinel Node, there is an increased risk of metastatic breast cancer which makes this evaluation crucial to decide what follow-up exams and therapy to follow. However, non-invasive detection of cancer cells in the lymph nodes is often inconclusive, leading to the surgical removal of too many nodes which causes adverse side-effects for patients. Microwave Imaging is one of the most promising non-invasive imaging modalities for breast cancer early screening and monitoring. This novel study tests the feasibility of imaging the axilla region by means of the simulation of an Ultra-Wideband Microwave Imaging system. Simulations of such system are completed in several 2D underarm models that mimic the axilla. Initial imaging results are obtained by means of processing the simulated backscattered signals by eliminating artefacts caused by the skin and beamforming the processed signals in order to time-align all the signals recorded at each antenna. In this dissertation several image formation algorithms are implemented and compared by visual inspection of the resulting images and through a range of performance metrics, such as Signal-to-Clutter Ratio and FullWidth Half Maximum calculations. The results in this study showed that Microwave Imaging is a promising technique that might allow to identify the presence and location of metastasised cancer cells in axillary lymph nodes, enabling the non-invasive evaluation of breast cancer staging.

Design of a low-voltage CMOS RF receiver for energy harvesting sensor node

In this thesis a CMOS low-power and low-voltage RF receiver front-end is presented. The main objective is to design this RF receiver so that it can be powered by a piezoelectric energy harvesting power source, included in a Wireless Sensor Node application. For this type of applications the major requirements are: the low-power and low-voltage operation, the reduced area and cost and the simplicity of the architecture. The system key blocks are the LNA and the mixer, which are studied and optimized with greater detail, achieving a good linearity, a wideband operation and a reduced introduction of noise. A wideband balun LNA with noise and distortion cancelling is designed to work at a 0.6 V supply voltage, in conjunction with a double-balanced passive mixer and subsequent TIA block. The passive mixer operates in current mode, allowing a minimal introduction of voltage noise and a good linearity. The receiver analog front-end has a total voltage conversion gain of 31.5 dB, a 0.1 - 4.3 GHz bandwidth, an IIP3 value of -1.35 dBm, and a noise figure lower than 9 dB. The total power consumption is 1.9 mW and the die area is 305x134.5 m2, using a standard 130 nm CMOS technology.

Non-gyrator type active inductors

Modern CMOS radio frequency (RF) Receivers have enabled efficient and increasing applications. The main requirement is to have system in a single chip, in order to minimize area and cost. For the purpose it is required the development of inductorless circuits for the key blocks of an RF receiver. Examples of this key blocks are RC oscillators, RF band pass filters, and Low Noise Amplifiers. The present dissertation presents an inductorless wideband MOSFET-only RF Non-Gyrator Type of Active Inductors with low area, low cost, and very low power, capable of covering the whole WMTS, and ISM, band and intended for biomedical applications. The proposed circuit is based on a floating capacitor connected between two controlled current sources. The first current source, which is controlled by the circuit input voltage, has two objectives: supply current to the capacitor (

8-Phase Ring oscillator for modern receivers

The evolution of receiver architectures, built in modern CMOS technologies, allows the design of high efficient receivers. A key block in modern receivers is the oscillator. The main objective of this thesis is to design a very low power and low area 8-Phase Ring Oscillator for biomedical applications (ISM and WMTS bands). Oscillators with multiphase outputs and variable duty cycles are required. In this thesis we are focused in 12.5% and 50% duty-cycles approaches. The proposed circuit uses eight inverters in a ring structure, in order to generate the output duty cycle of 50%. The duty cycle of 1/8 is achieved through the combination of the longer duty cycle signals in pairs, using, for this purpose, NAND gates. Since the general application are not only the wireless communications context, as well as industrial, scientific and medical plans, the 8-Phase Oscillator is simulated to be wideband between 100 MHz and 1 GHz, and be able to operate in the ISM bands (447 MHz-930 MHz) and WMTS (600 MHz). The circuit prototype is designed in UMC 130 nm CMOS technology. The maximum value of current drawn from a DC power source of 1.2 V, at a maximum frequency of 930 MHz achieved, is 17.54 mA. After completion of the oscillator layout studied (occupied area is 165 μm x 83 μm). Measurement results confirm the expected operating range from the simulations, and therefore, that the oscillator fulfil effectively the goals initially proposed in order to be used as Local Oscillator in RF Modern Receivers.