MOVLAB - Artigos de Revistas Internacionais com Arbitragem Científica

URI permanente para esta coleção:

http://hdl.handle.net/10437/11005

Navegar

A mostrar 1 - 20 de 24

Bayesian methodology for target tracking using combined RSS and AoA measurements
(Elsevier B.V., 2017) Tomic, Slavisa; Beko, Marko; Dinis, Rui; Tuba, Milan; Bacanin, Nebojsa; ECATI - School of Communication, Architecture, Arts and Information Technologies
This work addresses the target tracking problem based on received signal strength (RSS) and angle of arrival (AoA) measurements. The Bayesian methodology, which integrates the information given by observations with prior knowledge extracted from target motion model in order to enhance the estimation accuracy was employed. First, by converting the considered highly non-linear measurement model into a linear one, i.e., a novel linearization technique of the measurement model is proposed. The derived model is then merged with the prior knowledge, and a novel maximum a posteriori (MAP) estimator whose solution is given in closed-form is proposed. It is also shown that the Kalman filter (KF) can be directly applied on top of the linearized observation model, which results in a proposal of a novel KF algorithm. Furthermore, to the best of authors’ knowledge, this paper premierly presents the application of the extended KF (EKF) and the unscented KF (UKF) to the considered tracking problem, by applying first-order linearization technique to the original non-linear model, and by applying the unscented transformation to carefully selected sample points, respectively. Finally, importance weights are computed for a large number of randomly selected sample points to render a well-known particle filter (PF) solution. Simulation results show that the proposed algorithms perform better than a naive one which uses only information from observations. They also confirm the effectiveness of the proposed linearization technique in comparison with the existing one, reducing the estimation error for about 25%.
Target Tracking with Sensor Navigation Using Coupled RSS and AoA Measurements
(MDPI, 2017) Tomic, Slavisa; Beko, Marko; Dinis, Rui; Gomes, João Pedro; ECATI - School of Communication, Architecture, Arts and Information Technologies
This work addresses the problem of tracking a signal-emitting mobile target in wireless sensor networks (WSNs) with navigated mobile sensors. The sensors are properly equipped to acquire received signal strength (RSS) and angle of arrival (AoA) measurements from the received signal, while the target transmit power is assumed not known. We start by showing how to linearize the highly non-linear measurement model. Then, by employing a Bayesian approach, we combine the linearized observation model with prior knowledge extracted from the state transition model. Based on the maximum a posteriori (MAP) principle and the Kalman filtering (KF) framework, we propose new MAP and KF algorithms, respectively. We also propose a simple and efficient mobile sensor navigation procedure, which allows us to further enhance the estimation accuracy of our algorithms with a reduced number of sensors. Model flaws, which result in imperfect knowledge about the path loss exponent (PLE) and the true mobile sensors’ locations, are taken into consideration. We have carried out an extensive simulation study, and our results confirm the superiority of the proposed algorithms, as well as the effectiveness of the proposed navigation routine.
Global Female Jihadism: Far from the Paradise
(Global Journals, 2018) Pinto, José Filipe; ECATI - School of Communication, Architecture, Arts and Information Technologies
Terrorism, global terrorism, and global religious terrorism represent three different levels of the phenomenon. Despite the word «terrorism» being associated with a period of the French Revolution of 1789, terrorism is much older. However, global terrorism only dates back to almost 150 years, as it began with the anarchist wave (Rapoport, 2001) in the last decades of the 19th century, and global religious terrorism is the most recent wave as it started with the Islamic Revolution in Iran. In this evolution, the role of women in terrorism has changed over time, and when religion made its appearance in the phenomenon, it reached a crucial position, even in the communities where women are not regarded as man's equals. This paper provides a snapshot of global female jihadism. It points out the reasons for female attraction to terrorism. It also shows the roles that women play in terrorist groups. The argument of this paper is that, instead of paradise, female jihadists, mostly those who left west countries, discover hell on earth. Besides, the paper proves article suggests that they represent a challenge and a threat after following the breakdown of the ISIS caliphate.
Integrating innovation and technology : a case study
(Society of Sytematic Innovation, 2018) Marques, Pedro C.; Silva, Arlindo; Henriques, Elsa; FE - Faculty of Engineering
This paper explores a successful case of a product-service system (PSS). To meet the requirements of the client's needs and the existence of many technologies, business models and innovations involved in its conception and development, a conceptual framework of the ideation process is purposed to explain how the company met the requirements of such technical complexity, adding value to customers, stakeholders, and the company itself. Cases found in the development and implementation phase of the PSS displays the correspondence between the proposed framework and the case study. Furthermore, a relationship between creativity and systems' architecture is explored.
Exact Robust Solution to TW-ToA-Based Target Localization Problem With Clock Imperfections
(Institute of Electrical and Electronics Engineers Inc., 2018) Tomic, Slavisa; Beko, Marko; ECATI - School of Communication, Architecture, Arts and Information Technologies
This letter addresses the problem of target localization based on two-way time of arrival (TW-ToA) measurements with clock imperfections. In addition to the target location, the turn-around times and clock skews are considered unknown. Since an optimal estimator for this problem cannot be tackled directly, we approximate it by a suboptimal, robust one, formulated as a generalized trust region subproblem. Even though nonconvex in general, exact solution of the derived estimator can be obtained by just a bisection procedure. Simulation results validate the effectiveness of the proposed technique, matching the performance of the state of the art with significantly lower computational complexity.
Elephant Herding Optimization for Energy-Based Localization
(MDPI, 2018) Correia, Sérgio; Beko, Marko; Cruz, Luís Alberto da Silva; Tomic, Slavisa; COPELABS - Cognitive and People-centric Computing
This work addresses the energy-based source localization problem in wireless sensors networks. Instead of circumventing the maximum likelihood (ML) problem by applying convex relaxations and approximations, we approach it directly by the use of metaheuristics. To the best of our knowledge, this is the first time that metaheuristics are applied to this type of problem. More specifically, an elephant herding optimization (EHO) algorithm is applied. Through extensive simulations, the key parameters of the EHO algorithm are optimized such that they match the energy decay model between two sensor nodes. A detailed analysis of the computational complexity is presented, as well as a performance comparison between the proposed algorithm and existing non-metaheuristic ones. Simulation results show that the new approach significantly outperforms existing solutions in noisy environments, encouraging further improvement and testing of metaheuristic methods.
A bisection-based approach for exact target localization in NLOS environments
(Elsevier B.V., 2018-02) Tomic, Slavisa; Beko, Marko; CICANT - Centre for Research in Applied Communication, Culture, and New Technologies
This work addresses the range-based target localization problem in adverse non-line-of-sight (NLOS) environments. We start by deriving the maximum likelihood (ML) estimator from the measurement model, since it is asymptotically efficient. However, this estimator is highly non-convex and difficult to solve directly. Hence, we convert the localization problem into a generalized trust region sub-problem (GTRS) framework. Although still non-convex in general, the derived estimator is strictly decreasing over a readily obtained interval, and thus, can be solved exactly by a bisection procedure. In huge contrast to existing algorithms, which either require the knowledge about the magnitude of the NLOS bias or to a priori distinguish between line-of-sight (LOS) and NLOS links, the new one does not require such prerequisites. Also, the computational complexity of the proposed algorithm is linear in the number of reference nodes, unlike the majority of existing ones. Our simulation results show that the new algorithm possesses a steady NLOS bias mitigation capacity and that it represents an excellent alternative in the sense of the trade off between accuracy and complexity. To be more specific, it not only matches the performance of existing methods (majority of which significantly more computationally complex) but outperforms them in general. Moreover, the performance of the proposed algorithm is validated through real-indoor experimental data.
On Target Localization Using Combined RSS and AoA Measurements
(MDPI, 2018-04-19) Tomic, Slavisa; Beko, Marko; Dinis, Rui; Bernardo, Luís; COPELABS - Cognitive and People-centric Computing
This work revises existing solutions for a problem of target localization in wireless sensor networks (WSNs), utilizing integrated measurements, namely received signal strength (RSS) and angle of arrival (AoA). The problem of RSS/AoA-based target localization became very popular in the research community recently, owing to its great applicability potential and relatively low implementation cost. Therefore, here, a comprehensive study of the state-of-the-art (SoA) solutions and their detailed analysis is presented. The beginning of this work starts by considering the SoA approaches based on convex relaxation techniques (more computationally complex in general), and it goes through other (less computationally complex) approaches, as well, such as the ones based on the generalized trust region sub-problems framework and linear least squares. Furthermore, a detailed analysis of the computational complexity of each solution is reviewed. Furthermore, an extensive set of simulation results is presented. Finally, the main conclusions are summarized, and a set of future aspects and trends that might be interesting for future research in this area is identified.
Target localization in NLOS environments using RSS and TOA measurements
(IEEE Communications Society, 2018-12) Tomic, Slavisa; Beko, Marko; Tuba, Milan; Correia, Victor M.Franco; COPELABS - Cognitive and People-centric Computing
This letter addresses the problem of target localization in adverse non-line-of-sight environments. By utilizing integrated received signal strength and time of arrival measurements, a novel alternating algorithm is proposed. The new algorithm is derived by converting the original nonconvex problem into a generalized trust region sub-problem framework, which can be solved exactly by just a bisection procedure. Therefore, the proposed algorithm is very light in terms of computational cost, and its excellent estimation accuracy is validated through computer simulations.
Algorithms for estimating the location of remote nodes using Smartphones
(Institute of Electrical and Electronics Engineers Inc., 2019) Pedro, Dario; Tomic, Slavisa; Bernardo, Luís; Beko, Marko; Oliveira, Rodolfo; Dinis, Rui; Pinto, Paulo; Amaral, Pedro; COPELABS - Cognitive and People-centric Computing
Locating the position of a remote node on a wireless network is becoming more relevant, as we move forward in the Internet of things and in autonomous vehicles. This paper proposes a new system to implement the location of remote nodes. A new prototype Android application has been developed to collect real measurements and to study the performance of several smartphone's sensors and location algorithms, including an innovative one, based on the second order cone programming (SOCP) relaxation. The application collects theWiFi access points information and the terminal location. An internal odometry module developed for the prototype is used when Android's service is unavailable. This paper compares the performance of existing location estimators given in closed form, an existing SOCP one, and the new SOCP location estimator proposed, which has reduced complexity. An algorithm to merge measurements from non-identical terminals is also proposed. Cooperative and terminal stand-alone operations are compared, showing a higher performance for SOCP-based ones, that are capable of estimating the path loss exponent and the transmission power. The heterogeneous terminals were also used in the tests. Our results show that the accurate positioning of static remote entities can be achieved using a single smartphone. On the other hand, the accurate real-time positioning of the mobile terminal is provided when three or more scattered terminal nodes cooperate sharing the samples taken synchronously.
Target localization via integrated and segregated ranging based on RSS and TOA measurements
(MDPI, 2019) Tomic, Slavisa; Beko, Marko; COPELABS - Cognitive and People-centric Computing
This work addresses the problem of target localization in adverse non-line-of-sight (NLOS) environments by using received signal strength (RSS) and time of arrival (TOA) measurements. It is inspired by a recently published work in which authors discuss about a critical distance below and above which employing combined RSS-TOA measurements is inferior to employing RSS-only and TOA-only measurements, respectively. Here, we revise state-of-the-art estimators for the considered target localization problem and study their performance against their counterparts that employ each individual measurement exclusively. It is shown that the hybrid approach is not the best one by default. Thus, we propose a simple heuristic approach to choose the best measurement for each link, and we show that it can enhance the performance of an estimator. The new approach implicitly relies on the concept of the critical distance, but does not assume certain link parameters as given. Our simulations corroborate with findings available in the literature for line-of-sight (LOS) to a certain extent, but they indicate that more work is required for NLOS environments. Moreover, they show that the heuristic approach works well, matching or even improving the performance of the best fixed choice in all considered scenarios.
Dissimilar metals laserwelding between DP1000 steel and aluminum alloy 1050
(Multidisciplinary Digital Publishing Institute (MDPI), 2019) Pereira, António B.; Cabrinha, Ana; Rocha, Fábio; Marques, Pedro; Fernandes, Fábio A.O.; Alves de Sousa, Ricardo J.; FE - Faculty of Engineering; RCM2+ - Research Centre in Asset Management and System Engineering
The welding of dissimilar metals was carried out using a pulsed Nd: YAG laser to join DP1000 steel and an aluminum alloy 1050 H111. Two sheets of each metal, with 30 14 1 mm3, were lap welded, since butt welding proved to be nearly impossible due to the huge thermal conductivity differences and melting temperature differences of these materials. The aim of this research was to find the optimal laser welding parameters based on the mechanical and microstructure investigations. Thus, the welded samples were then subjected to tensile testing to evaluate the quality of the joining operation. The best set of welding parameters was replicated, and the welding joint obtained using these proper parameters was carefully analyzed using optical and scanning electron microscopes. Despite the predicted difficulties of welding two distinct metals, good quality welded joints were achieved. Additionally, some samples performed satisfactorily well in the mechanical tests, reaching tensile strengths close to the original 1050 aluminum alloy.
A survey on sustainable product development
(Elsevier B.V., 2019) Marques, Pedro Carmona; Charmier, Maria Adília Januário; Santos, José Oliveira; FE - Faculty of Engineering
The emergent field of sustainable product development has been rapidly evolving in several academic publications. Furthermore, sustainable product development is the basis for innovative products (and services). The analysis begins by identifying published studies within the last five years. A systematic mapping of the field evolution overtime is performed by identifying areas of current research interests and potential directions for future research. The findings will provide a roadmap for further investigations in this field.
Computational programming as a tool in the teaching of electromagnetism in engineering courses : Improving the notion of field
(Multidisciplinary Digital Publishing Institute (MDPI), 2019) Nogueira, João; Alves, Ricardo Gaio; Marques, Pedro Carmona; FE - Faculty of Engineering; CeiED - Interdisciplinary Research Centre for Education and Development
In this study we have attempted, firstly, to describe programming protocols developed for the teaching of an Electromagnetism course in the university degrees of Electrical Engineering and Energy Engineering, and secondly, to evaluate students’ satisfaction with the simulation practices through MATLAB®programming. The main objective of the protocols is to allow students to model and visualize the electric field and magnetic field (both static) and understand the approximation that is made when considering certain distributions of electric charges and electric currents. To evaluate the usefulness of this computational methodology, eighteen students from the two engineering degrees answered a questionnaire with seven questions related to the Electromagnetism course and to the benefits of using computer programming. Their answers are measured by a Likert scale. From the analysis of the results, we can conclude, in a general way, that the use of this methodology has positive effects in the learning of Electromagnetism in these two degrees.
Estimating directional data from Network Topology for improving tracking performance
(Multidisciplinary Digital Publishing Institute (MDPI), 2019) Tomic, Slavisa; Beko, Marko; Dinis, Rui; Montezuma, Paulo; COPELABS - Cognitive and People-centric Computing
This work proposes a novel approach for tracking a moving target in non-line-of-sight (NLOS) environments based on range estimates extracted from received signal strength (RSS) and time of arrival (TOA) measurements. By exploiting the known architecture of reference points to act as an improper antenna array and the range estimates, angle of arrival (AOA) of the signal emitted by the target is first estimated at each reference point. We then show how to take advantage of these angle estimates to convert the problem into a more convenient, polar space, where a linearization of the measurement models is easily achieved. The derived linear model serves as the main building block on top of which prior knowledge acquired during the movement of the target is incorporated by adapting a Kalman filter (KF). The performance of the proposed approach was assessed through computer simulations, which confirmed its effectiveness in combating the negative effect of NLOS bias and superiority in comparison with its naive counterpart, which does not take prior knowledge into consideration.
A robust NLOS bias mitigation technique for RSS-TOA-based target localization
(Institute of Electrical and Electronics Engineers Inc., 2019-01) Tomic, Slavisa; Beko, Marko; COPELABS - Cognitive and People-centric Computing
This letter proposes a novel robust mitigation technique to address the problem of target localization in adverse non-line-of-sight (NLOS) environments. The proposed scheme is based on combined received signal strength and time of arrival measurements. Influence of NLOS biases is mitigated by treating them as nuisance parameters through a robust approach. Due to a high degree of difficulty of the considered problem, it is converted into a generalized trust region sub-problem by applying certain approximations, and solved efficiently by merely a bisection procedure. Numerical results corroborate the effectiveness of the proposed approach, rendering it the most accurate one in all considered scenarios.
A linear estimator for network localization using integrated RSS and AOA measurements
(Institute of Electrical and Electronics Engineers Inc., 2019-03) Tomic, Slavisa; Beko, Marko; Tuba, Milan; COPELABS - Cognitive and People-centric Computing
This letter addresses the problem of simultaneous localization of multiple targets in three-dimensional cooperative wireless sensor networks. To this end, integrated received signal strength and angle of arrival measurements are employed. By exploiting the convenient nature of spherical representation of the considered problem, the measurement models are linearized and a sub-optimal estimator is formulated. Unlike the maximum likelihood estimator, which is highly non-convex and difficult to tackle directly, the derived estimator is quadratic and has a closed-form solution. Its computational complexity is linear in the number of connections and its accuracy surpasses the accuracy of existing ones in all considered scenarios.
The siren song of populism
(Global Journals, 2019-03) Pinto, José Filipe; ECATI - School of Communication, Architecture, Arts and Information Technologies
Populism is not a fad or an epiphenomenon. As the election results prove, populism is increasing almost all over the world, and populists rule the four most crowed democracies. Populist parties are gaining ground in the majority of the EU countries and in the two latest American presidential elections two populists – Donald Trump and Bolsonaro – achieved the power stage of the USA and Brazil. In the European Union, after a long period, while populist parties assumed an anti-system position, most of the populists changed their strategy trying to reach the power, and they are already the third political force. This increase has been constant. However, the economic recession and the large flow of refugees and immigrants were at the roof of the most recent rise. The essay analyses the populist parties’ strategic change and the reaction of the mainstream parties. It also explains that right-wing populism is using the nationalist rhetoric and some policies of social democracy into the service of nationalism, and it is increasing faster than the left-wing one. Moreover, the essay shows that populist governments stay in power longer than non-populists do. Finally, it proves that the populist discourse works as a new siren song because populist leaders say what the citizens are keen to hear
Special issue : localization in wireless sensor networks
(Multidisciplinary Digital Publishing Institute (MDPI), 2020) Tomic, Slavisa; Beko, Marko; COPELABS - Cognitive and People-centric Computing
Exploiting orientation information to improve range-based localization accuracy
(Institute of Electrical and Electronics Engineers Inc., 2020) Tomic, Slavisa; Beko, Marko; Tuba, Milan; COPELABS - Cognitive and People-centric Computing
This work addresses target localization problem in precarious surroundings where possibly no links are line of sight. It exploits the known architecture of available reference points to act as an irregular antenna array in order to estimate the azimuth angle between a reference point and a target, based on distance estimates withdrawn from integrated received signal strength (RSS) and time of arrival (TOA) observations. These fictitious azimuth angle observations are then used to linearize the measurement models, which triggers effortless derivation of a new estimator in a closed-form. It is shown here that, by using fixed network geometry in which target orientation with respect to a line formed by a pair of anchors can be correctly estimated, the localization performance can be significantly enhanced. The new approach is validated through computer simulations, which corroborate our intuition of profiting from inherent information within a network.

Navegar

Percorrer MOVLAB - Artigos de Revistas Internacionais com Arbitragem Científica por data de Publicação

Resultados por página

Opções de ordenação