ESTG - Comunicações em conferências e congressos internacionais
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- A 1.2V 900nW conductance converterPublication . Miranda, Nuno; Morais, RaulThis article describes a new electrical conductance converter method suitable for very low power applications, where energy constraints prevails over speed and measurement accuracy. Method idea gather voltage time integration and shopper stabilization techniques to process noisy low amplitude signals and to overcome severe limitations of weak inversion channel CMOS circuitry. Main features and tradeoffs are exploited. A 1.2V ASIC implementation on standard 0.35μm CMOS schematics is also presented. Post-layout simulations shows a total power consumption lower than 900nW including current source excitation inherent to the conductance measurement. Such low power consumption allows the measurement of several physical parameters on self-powered wireless networks.
- 802.21-MPA-IMS ArchitecturePublication . Rodrigues, Carlos Miguel de Jesus; Rabadão, Carlos; Pereira, AntónioMobility has become a keyword nowadays with the evolution of mobile devices market and proliferation of realtime services. IP Multimedia Subsystem (IMS) is a single, standardized service framework that supports voice, video, data and messaging services, but does not provide seamless mobility for packet based sessions. This paper purposes an IMS architecture with IEEE 802.21 and media-independent pre-authentication (MPA) integrated. IEEE 802.21 can enable this seamless mobility in IMS and, additionally, MPA provides a secure handover optimization scheme, reducing, as a consequence, handover latency. The main goal of this architecture is to provide seamless and secure handovers between different access technologies in an IMS-based environment.
- Acoustic Similarity Scores for Keyword SpottingPublication . Veiga, Arlindo; Lopes, Carla; Sá, Luís; Perdigão, FernandoThis paper presents a study on keyword spotting systems based on acoustic similarity between a filler model and keyword model. The ratio between the keyword model likelihood and the generic (filler) model likelihood is used by the classifier to detect relevant peaks values that indicate keyword occurrences. We have changed the standard scheme of keyword spotting system to allow keyword detection in a single forward step. We propose a new loglikelihood ratio normalization to minimize the effect of word length on the classifier performance. Tests show the effectiveness of our normalization method against two other methods. Experiments were performed on continuous speech utterances of the Portuguese TECNOVOZ database (read sentences) with keywords of several lengths.
- Ad-hoc changes in IoT-aware business processesPublication . Domingos, Dulce; Martins, Francisco; Martinho, Ricardo; Silva, MárioThe Internet of Things makes it possible to adapt the behaviour of business processes in response to real-time context updates. In addition, physical items can run and validate parts of the business processes and optimise their execution, while reducing message transmissions. State-of-the-art event-driven, service-oriented architecture approaches contribute to enabling inter-organisational collaboration and interoperability of heterogeneous hardware, but their applicability is limited to preplanned, well-structured processes. We take a step forward by supporting ad-hoc changes within business processes, considering changes in the state of the Things; likewise, whenever needed, the software controlling the behaviour of sensors may be dynamically reconfigured as a result of changes in the functional specifications of business processes.
- An adaptive strategy for improving the performance of genetic programming-based approaches to evolutionary testingPublication . Ribeiro, José; Zenha-Rela, Mário Alberto; Vega, Francisco Fernández deThis paper proposes an adaptive strategy for enhancing Genetic Programming-based approaches to automatic test case generation. The main contribution of this study is that of proposing an adaptive Evolutionary Testing methodology for promoting the introduction of relevant instructions into the generated test cases by means of mutation; the instructions from which the algorithm can choose are ranked, with their rankings being updated every generation in accordance to the feedback obtained from the individuals evaluated in the preceding generation. The experimental studies developed show that the adaptive strategy proposed improves the algorithm's efficiency considerably, while introducing a negligible computational overhead.
- Alternative Zigbee codes derived from orthogonal perfect DFT sequencesPublication . Pereira, João S.; Silva, Henrique J. A. daThe performance of a code-division multiple access (CDMA) system is directly related with the choice of adequate codes. The codes for use in CDMA communication systems should have a perfect aperiodic (or periodic) autocorrelation function and should be orthogonal to each other at all time shifts. A mathematical property that provides a way to find large sets of real perfect DFT (discrete Fourier transform) sequences is presented. These sequences can be transformed into real orthogonal perfect DFT sequences and also into bipolar codes that have better properties than the codes used in the Zigbee communication system. These new bipolar codes are approximately orthogonal and have nearly optimum periodic and aperiodic autocorrelation functions. We also evaluate our bipolar codes with an improved error probability model.
- Analysis of Radiowave Propagation in Forest Media Using the Parabolic EquationPublication . Ramos, Glaucio L.; Pereira, Paulo T.; Leonor, Nuno; Caldeirinha, Rafael F. S.This paper presents preliminary results about path loss prediction in vegetation using the parabolic equation technique. The trees were modelled in a flat and a triangular format and their effect in the path loss was analysed. A real measurement scenario with trees was also modelled and compared with the PE simulation. The use of the parabolic equation method to study the path loss attenuation in forest environments seems to be very promise.
- An Approach to Assess the Performance of Mobile Applications: A Case Study of Multiplatform Development FrameworksPublication . Mota, Dany; Martinho, RicardoComparative studies between software multiplatform development frameworks lack a proper approach that can be replicated in future performance assessments. Moreover, there is still a deficit in performance comparison tools. Also, performance comparisons realized between mobile applications developed under these multiplatform frameworks should be done with applications running in Release Mode, which ends up not happening in most studies. The objective of this paper is thus to create a whole comparative process as correct and stable as possible, so that we can use it to safely assess performance of mobile applications developed with these frameworks. As a case study, we compare the well-known Flutter and React Native frameworks, and present the obtained results under the proposed approach. With this work, developers can not only assess both these particular frameworks, but also use the approach for further comparisons.
- Architectural Challenges on the Integration of e-Commerce and ERP Systems: A Case StudyPublication . Santos, Fábio; Martinho, RicardoMany retail companies had to go online before their Enterprise Resource Planning (ERP)-type systems were ready to fulfill all business requirements. Their overall daily operation still heavily depends on these highly customized systems often mandatory because of legal obligations, which frequently come without e-commerce “off the shelf” integration. This paper identifies main challenges derived out of the architectural and integration requirements from a case study at an e-tailer company that operates via two sales channels: online store and third-party marketplaces. These challenges led to the definition of a system architecture and implementation considerations for this common integration scenario, which was validated through its implementation. Our proposed approach allows ERP-dependent organizations to start selling online with open-source technologies, avoiding extra ERP licensing and hidden maintenance costs.
- An Artificial Immune System for Temporal Anomaly Detection Using Cell Activation Thresholds and Clonal Size Regulation with HomeostasisPublication . Antunes, Mário; Correia, Manuel E.This paper presents an Artificial Immune System (AIS) based on Grossman's Tunable Activation Threshold (TAT) for anomaly detection. We describe the immunological metaphor and the algorithm adopted for T-cells, emphasizing two important features: the temporal dynamic adjustment of T-cells clonal size and its associated homeostasis mechanism. We present some promising results obtained with artificially generated data sets, aiming to test the appropriateness of using TAT in dynamic changing environments, to distinguish new unseen patterns as part of what should be detected as normal or as anomalous.