Movlab – Laboratory of Technologies for Interactions and Interfaces

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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 (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
Distributed localization with complemented RSS and AOA measurements : Theory and methods
(Multidisciplinary Digital Publishing Institute (MDPI), 2020-01-01) Tomic, Slavisa; Beko, Marko; Matos, Luís M. Camarinha de; Oliveira, Luís Bica; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
Remarkable progress in radio frequency and micro-electro-mechanical systems integrated circuit design over the last two decades has enabled the use of wireless sensor networks with thousands of nodes. It is foreseen that the fifth generation of networks will provide significantly higher bandwidth and faster data rates with potential for interconnecting myriads of heterogeneous devices (sensors, agents, users, machines, and vehicles) into a single network (of nodes), under the notion of Internet of Things. The ability to accurately determine the physical location of each node (stationary or moving) will permit rapid development of new services and enhancement of the entire system. In outdoor environments, this could be achieved by employing global navigation satellite system (GNSS) which offers a worldwide service coverage with good accuracy. However, installing a GNSS receiver on each device in a network with thousands of nodes would be very expensive in addition to energy constraints. Besides, in indoor or obstructed environments (e.g., dense urban areas, forests, and canyons) the functionality of GNSS is limited to non-existing, and alternative methods have to be adopted. Many of the existing alternative solutions are centralized, meaning that there is a sink in the network that gathers all information and executes all required computations. This approach quickly becomes cumbersome as the number of nodes in the network grows, creating bottle-necks near the sink and high computational burden. Therefore, more effective approaches are needed. As such, this work presents a survey (from a signal processing perspective) of existing distributed solutions, amalgamating two radio measurements, received signal strength (RSS) and angle of arrival (AOA), which seem to have a promising partnership. The present article illustrates the theory and offers an overview of existing RSS-AOA distributed solutions, as well as their analysis from both localization accuracy and computational complexity points of view. Finally, the article identifies potential directions for future research.
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 (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
Exploiting orientation information to improve range-based localization accuracy
(Institute of Electrical and Electronics Engineers Inc., 2020) Tomic, Slavisa; Beko, Marko; Tuba, Milan; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
A geometric approach for distributed multi-hop target localization in cooperative networks
(Institute of Electrical and Electronics Engineers Inc., 2020-01) Tomic, Slavisa; Beko, Marko; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
This work addresses target localization problem in cooperative distributed sensor networks, in which all sensors are capable of measuring Received Signal Strength (RSS), but only some are appropriately equipped to measure Angle Of Arrival (AOA) of the received signal. A novel approach based on simple geometry and multi-hopping is proposed, which allows for natural conversion of the problem into a Generalized Trust Region Sub-Problem (GTRS). The proposed algorithm comprises three main steps, each of them with linear computational cost in the number of neighbors, making it suitable for real-time applications. Our simulation results validate the performance of the new algorithm, surpassing some significantly more complex ones, and almost achieving a lower bound set by an existing algorithm which uses some (unrealistic) assumptions in its favor.
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 (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
On Target Localization Using Combined RSS and AoA Measurements
(MDPI, 2018-04-19) Tomic, Slavisa; Beko, Marko; Dinis, Rui; Bernardo, Luís; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
PyXYZ : an educational 3D wireframe engine in Python
(Association for Computing Machinery, 2021-06-26) Fachada, Nuno; Andrade, Diogo Nuno Dias Mesquita Gomes de; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
In this paper we introduce PyXYZ, a 3D wireframe software rendering framework for educational purposes. The main goal of this framework is to provide a simple-to-understand tool that students can use to build a more sophisticated engine, while learning mathematics and acquiring a deeper knowledge of the complexity of a modern 3D engine. PyXYZ can be used as a teaching aid in course work and/or as a template for multi-goal project assignments, allowing students with diverse capabilities and interests to have different levels of commitment. The engine has been used with positive results in a mathematics course unit of a computer games BA and can be easily adapted to various teaching scenarios.
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 (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
Special issue : localization in wireless sensor networks
(Multidisciplinary Digital Publishing Institute (MDPI), 2020) Tomic, Slavisa; Beko, Marko; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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 (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
Target localization via integrated and segregated ranging based on RSS and TOA measurements
(MDPI, 2019) Tomic, Slavisa; Beko, Marko; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS)
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.
The uncanny valley, notes on the realism of “living” creatures in digital games and their relationships with the player : O vale da estranheza, notas sobre o realismo das criaturas "vivas" nos jogos digitais e a sua relação com o jogador
(Universidade Católica Portuguesa, 2008) Luz, Filipe Costa; Abrantes, João M. C. S.; Damásio, Manuel José; Gouveia, Patrícia; Escola de Comunicação, Arquitetura, Artes e Tecnologias da Informação; HEI-LAB (FCT) - Digital Laboratories for Environments and Human Interactions; COPELABS (FCT) - Centro de Investigação em Computação Centrada nas Pessoas e Cognição (CTS); Universidade Lusófona
Neste artigo argumenta-se que as simulações numéricas fomentam e exploram relações complexas entre o jogador e o sistema cibernético da máquina que com este se relaciona através da jogabilidade, ou seja, da real aplicação às regras de jogo de tácticas e estratégias usadas pelo participante durante o seu trajecto na aplicação lúdica. Considera-se que o espaço mágico imposto pelo tabuleiro de jogo é mais do que um espaço de confusão entre real e artificial mas antes se apresenta como uma cortina ou interface entre o corpo próprio do participante e a simulação digital inerente ao sistema computacional.

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