Browsing by Author "Albuquerque, Daniel"
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- Accurate Spectral Estimation of Non-periodic Signals Based on Compressive SensingPublication . Duarte, Isabel M. P.; Vieira, José M. N.; Ferreira, Paulo J S G; Albuquerque, DanielIn this work we propose a method based on compressive sensing (CS) for estimating the spectrum of a signal written as a linear combination of a small number of sinusoids. In practice one deals with signals with finite-length and so the Fourier coefficients are not exactly sparse. Due to the leakage effect in the case where the frequency is not a multiple of the fundamental frequency of the DFT, the success of the traditional CS algorithms is limited. To overcome this problem our algorithm transform the DFT basis into a frame with a larger number of vectors, by inserting a small number of columns between some of the initial ones. The algorithm takes advantage of the compactness of the interpolation function that results from the ‘1 norm minimization of the Basis Pursuit (BP) and is based on the compressive sensing theory that allows us to acquire and represent sparse and compressible signals, using a much lower sampling rate than the Nyquist rate. Our method allow us to estimate the sinusoids amplitude, phase and frequency.
- Cityaction a smart-city platform architecturePublication . Martins, Pedro; Albuquerque, Daniel; Wanzeller, Cristina; Caldeira, Filipe; Tomé, P.; Sá, FilipeFast population growth in cities and surrounding regions force cities to become smarter to have a sustainable economy, social quality, and environmental well-being. Smart-Cities will be the ones using information and communication technologies to make cities services more efficient (in performance and cost), interactive, and aware of events. For a city to become smarter, it needs to make use of emerging technologies related with Internet-of-Things (IoT), not only to collect information and interact (actuate, command, control) but also to provide services for analytics and other applications. In this paper, is researched the concept of smart-city in the context of the project CityAction, tested on the city of Castelo Branco, Portugal. This project focuses on the relationship between IoT, monitoring, actuating and displaying data. Based on collected data from sensors spread across the city, the proposed project aims to make “smart” decisions to optimize resources, cost, well living, and environmental impact. Results introduce an architecture to integrate multiple heterogeneous sensors, develop a dashboard able of displaying data in a user-friendly way, and making this information available to population and users through a mobile app. This mechanism makes possible to infer better decisions on the city management/behavior and put in place the needed mechanisms to improve response time, safety and well living.
- Flexible Power Control of Photovoltaic Plants Connected to Distribution NetworksPublication . Ribeiro, Susana; Costa, Paulo Moisés; Gouveia, Eduardo; Sousa, Pedro; Albuquerque, DanielThis paper presents a system to control the power injected by a photovoltaic (PV) plant on the receiving network. This control is intended to mitigate some of the negative impacts that these units may produce on such networks, while increasing the installed power of the plant. The controlled parameters are the maximum allowed value of injected active power and the corresponding power factor, whose setpoints values may be fixed or dynamic. The developed system allows a local and a remote control. The injected power and the corresponding power factor may be set by following a predetermined profile or by real time adjustments to fulfill specific operation constraints on the receiving network. The system acts by adjusting the control parameters on the PV inverters. The main goal of the system is, in the end, to control the PV plant, ensuring the accomplishment of technical constraints and, at the same time, maximizing the installed power of the PV plant, which may be an important issue concerning the economic performance of such plants
- High Energy OFDM Pulse Design Algorithm for Acoustic ToF Ranging and LocalizationPublication . Albuquerque, Daniel; Vieira, José; Lopes, Sérgio; Aguilera, Teodoro; Álvarez, FernandoThis paper proposes an algorithm to design band-limited Orthogonal Frequency Division Multiplexing (OFDM) pulses for accurate time-of-flight ranging in acoustic-based localization systems. The proposed algorithm is capable to generate OFDM pulses with higher energy when compared with other common pulse design approaches with similar characteristics. The results attained have shown that it is possible to design OFDM pulses with 17% more energy than a chirp or a BPSK pulse with the same characteristics. The proposed algorithm uses an iterative approach to increase the pulse energy while keeping the same amplitude, bandwidth and duration in each iteration. Two different OFDM pulses are provided and compared with two common pulses, namely chirp and BPSK pulses, with the same characteristics.
- High Resolution Spectral Estimation using BP via Compressive SensingPublication . Duarte, Isabel; Vieira, José M. N.; Ferreira, Paulo J S G; Albuquerque, DanielIn this paper we propose a method based on compressed sensing (CS) for estimating the spectrum of a signal written as a linear combination of a small number of sinusoids. In the case of finite-length signals, the Fourier coefficients are not exactly sparse due to the leakage effect if the frequency is not a multiple of the fundamental frequency; To overcome this problem our algorithm transform the DFT basis into a frame with a larger number of vectors, by inserting columns between some of the initial ones. The algorithm applies Basis Pursuit (BP) to estimate the sinusoids amplitude, phase and frequency.
- Indoor Location Using UltrasoundsPublication . Albuquerque, Daniel; Vieira, José; Bastos, Carlos; Ferreira, PauloThis thesis presents a location system based exclusively on ultrasonic signals, without using any other technology. This location system was designed to operate in environments where the use of other technologies is not possible or the use of them is limited, such as underwater applications or hospital environments. The proposed location system uses a network of fixed beacons allowing the mobile stations to locate. Due to the necessity of data transmission and distance measurement an ultrasonic pulse robust to echoes was developed that allows to perform both tasks with success. The location system allows that mobiles locate themselves only listening to the information in the ultrasonic pulse sent by the beacons, for that an algorithm based on time difference of arrival is used. Therefore, the user privacy is guaranteed as well as the complete independence of the system number of users. To simplify the network implementation it is only necessary to manually define the position of some of the beacons, called anchor beacons. These will allow the remaining autonomous beacons to locate themselves by an iterative location algorithm based on a local cost function minimization. For this system to work properly the beacons must synchronize their clocks and measure the distance between them. Therefore, this thesis proposes a clock synchronization protocol which also allows to measure the distance between the beacons by exchanging only three ultrasonic messages. Additionally, the location system permits that damaged beacons may be replaced without compromising the network operability reducing the maintenance complexity. Additionally, a simplified ultrasonic simulator for indoor environments was developed, which has proved to be very accurate and a valuable tool to simulate the location system behavior under controlled conditions.
- Iterative Algorithm for High Resolution Frequency EstimationPublication . Duarte, Isabel M. P.; Vieira, José M. N.; Ferreira, Paulo J S G; Albuquerque, DanielCompressed sensing (CS) is a theory that allows us to recover sparse or compressible signals from a much smaller number of samples or measurements than with traditional methods. The problem of detection and estimation of the frequency of a signal is more difficult when the frequencies of the signal are not present on the DFT basis. The Fourier coefficients are not exactly sparse due to the leakage effect if the frequency is not a multiple of the fundamental frequency. In this work we present a high frequency resolution spectrum estimation algorithm that explores the CS, for this type of nonperiodic signal from finite number of samples. It takes advantage of the sparsity of the signal in the frequency domain. The algorithm transforms the DFT basis into a frame with a large number of vectors by inserting columns between some of the existing ones. The proposed algorithm can estimate the amplitudes and frequencies even when the frequencies are too close together, a particularly difficult situation which are not covered by most of the known algorithms. Simulation results show good convergence and a high resolution when compared with other algorithms
- LowCost system architecture for monitoring environmental parameters in circulating automotive roadsPublication . Costa, João; Wanzeller, Cristina; Albuquerque, Daniel; Caldeira, Filipe; Tomé, P.; Martins, PedroA qualidade de vida nas cidades é cada vez mais uma preocupação. A análise de parâmetros ambientais é nesta base uma preocupação ao nível das entidades responsáveis pela gestão das cidades. Neste artigo apresenta-se uma arquitetura de um sistema de baixo custo para monitorização de parâmetros ambientais em vias de circulação das cidades. Palavras Chave – Cidades Inteligentes, IoT, Arquitetura de Sistema. Abstract — The quality of life in cities is nowadays a concern. The city management authorities usually are concernd with the environmental parameters. This article presents an architecture of a low-cost system for monitoring environmental parameters in Automotive Roads.
- NoSQL Scalability Performance Evaluation over CassandraPublication . Abbasi, Maryam; Sá, Filipe; Albuquerque, Daniel; Wanzeller, Cristina; Caldeira, Filipe; Tomé, P.; Furtado, Pedro; Martins, PedroThe implementation of Smart-Cities is growing all over the world. From big cities to small villages, information able to provide a better and efficient urban management is collected from multiple sources (sensors). Such information has to be stored, queried, analyzed and displayed, aiming to contribute to a better quality of life for citizens and also a more sustainable environment. In this context it is important to choose the right database engine for this scenario. NoSQL databases are now generally accepted by the database community to support application niches. They are known for their scalability, simplicity, and key-indexed data storage, thus, allowing an easy data distribution and balancing over several nodes. In this paper a NoSQL engine is tested, Cassandra, which is one of the most scalable, amongst most NoSQL engines and therefore, a candidate for use in our application scenario. The paper focuses on horizontal scalability, which means that, by adding more nodes, it is possible to respond to more requests with the same or better performance, i.e., more nodes mean reduced execution time. Although, adding more computational resources, does not always result in better performance. This work assesses how each workload (e.g., data volume, simultaneous users) influence scalability performance. An overview of the Cassandra database engine is presented in the paper. Following, it will be tested and evaluated using the benchmark Yahoo Cloud Serving Benchmark (YCSB).
- TheremUS: the Ultrasonic ThereminPublication . Gomes, André; Albuquerque, Daniel; Campos, Guilherme; Vieira, JoséIn the Theremin, the performer’s hand movements, detected by two antennas, control the pitch and volume of the generated sound. The TheremUS builds on this concept by using ultrasonic sensing for hand position detection and processing all signals digitally, a distinct advantage in terms of versatility. Not only can different sound synthesis algorithms be programmed directly on the instrument but also it can be easily connected to other digital sound synthesis or multimedia devices; a MIDI interface was included for this purpose. The TheremUS also features translucent panels lit by controllable RGB LED devices. This makes it possible to specify sound-colour mappings in the spirit of the legendary Ocular Harpsichord by Castel.