ISEL - Eng. Elect. Tel. Comp. - Artigos
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- A new methodology for evaluating the neighbor discovery time in schedule-based asynchronous duty-cycling wireless sensor networksPublication . Passos, Diego; Trabbold, Beatriz; Carrano, Ricardo C.; Sousa, Cledson deDuty cycling is a fundamental mechanism for battery-operated wireless networks, such as wireless sensor networks. Due to its importance, it is an integral part of several Medium Access Protocols and related wireless technologies. In Schedule-based Asynchronous Duty Cycle, nodes activate and deactivate their radio interfaces according to a pre-designed schedule of slots, which guarantees overlapping uptime between two neighbors, independent of the offset between their internal clocks, making communication between them possible. This paper presents a new methodology for evaluating the Neighbor Discovery Time (NDT) of Schedule-based Asynchronous Duty Cycle. Differently from previous methodologies, it accounts for the possibility of the slots in the schedules of the two neighbors not being perfectly border-aligned - an unrealistic assumption in practice. By means of simulation, we show that not taking this under consideration can lead to an overestimate of the NDT by a factor of 2 depending on the particular scenario, thus justifying the importance of our work. center dot We propose a new subslot-based methodology for computing the NDT of a wakeup schedule used for asynchronous duty cycling. center dot It replaces the traditional slot-based methodology, by dividing slots into subslots, allowing for the analysis of non-integer clock offsets between nodes, and further allowing mathematical models to consider the more realistic continuous-time case. center dot Our validation data shows that the slot-based methodology may overestimate NDT by a factor of up to 2, making the proposed subslot-based methodology much more precise.
- An autonomic parallel strategy for exhaustive search tree algorithms on shared or heterogeneous systemsPublication . Gonçalves de Oliveira Passos, Fernanda; Rebello, Vinod E. F.Backtracking branch-and-prune (BP) algorithms and their variants are exhaustive search tree techniques widely employed to solve optimization problems in many scientific areas. However, they characteristically often demand significant amounts of computing power for problem sizes representative of real-world scenarios. Given that their search domains can often be partitioned, these algorithms are frequently designed to execute in parallel by harnessing distributed computing systems. However, to achieve efficient parallel execution times, an effective strategy is required to balance the nonuniform partition workloads across the available resources. Furthermore, with the increasing integration of servers with heterogeneous resources and the adoption of resource sharing, balancing workloads is becoming complex. This paper proposes a strategy to execute parallel BP algorithms more efficiently on even shared or heterogeneous distributed systems. The approach integrates a self-adjusting dynamic partitioning method in the BP algorithm with a dynamic scheduler, provided by an application middleware, which manages the parallel execution while addressing any issues of imbalance. Empirical results indicate better scalability with efficiencies above 90% for instances of an application case study for the discretizable molecular distance geometry problem (DMDGP). Improvements of up to 38% were obtained in execution speed-ups compared to a more traditional parallel BP implementation for DMDGP.
- Intelligent sports weightsPublication . Duarte, Olga dos Santos; Jacinto, Gustavo; Véstias, Mário; Véstias, Mário; Duarte, Rui Policarpo; Duarte, RuiWeightlifting is a common fitness activity and can be practiced individually without supervision. However, performing regular weightlifting exercises without any form of feedback can lead to serious injuries. To counter this, this work proposes a different approach to automatic weightlifting supervision off-the-person. The proposed embedded system is coupled to the weights and evaluates if they follow the correct trajectory in real time. The system is based on a low-power embedded System-on-a-Chip to perform the classification of the correctness of physical exercises using a Convolutional Neural Network with data from the embedded IMU. It is a low-cost solution and can be adapted to the characteristics of specific exercises to fine-tune the performance of the athlete. Experimental results show real-time monitoring capability with an average accuracy close to 95%. To favor its use, the prototypes have been enclosed on a custom 3D case and validated in an operational environment. All research outputs, developments, and engineering models are publicly available.
- Integration of visible light communication, artificial intelligence, and rerouting strategies for enhanced urban traffic managementPublication . Vieira, Manuela; Galvão, Gonçalo; Vieira, Manuel Augusto; Véstias, Mário; Vieira, Pedro; Louro, PaulaThis study combines Visible Light Communication (VLC) and Artificial Intelligence (AI) to enhance traffic signal control, reduce congestion, and improve safety, through real-time monitoring and dynamic traffic management. Leveraging VLC technology, the system uses existing road infrastructure to transmit live data on vehicle and pedestrian positions, speeds, and queues. AI agents, employing Deep Reinforcement Learning (DRL), process this data to manage traffic flows dynamically, applying anti-bottleneck and rerouting techniques to balance pedestrian and vehicle waiting times. A centralized global agent coordinates the local agents controlling each intersection,enabling indirect communication and data sharing to train a unified DRL model. This model makes real-time adjustments to traffic light phases, utilizing a queue/request/response system for adaptive intersection management. Tested using simulations and real-world trials involving standard and rerouting scenarios, the approach demonstrates significantly better performance in regard to the rerouting configuration, reducing congestion and enhancing traffic flow and pedestrian safety.Scalable and adaptable to various intersection types, including four-way, T-intersections, and roundabouts, the system’s efficacy is validated using the SUMO urban mobility simulator, resulting in notable reductions to travel and waiting times for both vehicles and pedestrians.
- Preparing students for the software industry new demandsPublication . Metrôlho, José Carlos; Ribeiro, Fernando; Batista, Rodrigo; Graça, Paula; Pacheco, DiogoA solid preparation in terms of soft skills and state-of-the-art technical skills in Software Engineering (SE) is a goal for the academy. It also contributes to reducing the gap between Software Engineering education and the software industry's new demands. Generally, in computer science or computer engineering courses, there are separate subjects to teach requirements engineering, analysis, design, coding, or validation. However, integrating all these subjects usually requires experience in developing a complete project. This article describes aspects of an active and collaborative learning approach involving academia and industry actors. The approach presented in this article involved staff from a software company in collaboration with staff from an academic institution. It resulted in a student being involved in an entire software development project. The student was involved in an agile team of faculty and Information Technology (IT) professionals. The Scrum agile framework was followed, and the product was developed using a Low-code development platform. This article presents the approach, details of the project design and implementation, results achieved, lessons learned, and guidelines for the future. The results show that this agile, full-stack approach allows students to develop cutting edge technical and non-technical skills.
- On the Use of Spatial Graphs for Performance Degradation Root-Cause Analysis Toward Self-Healing Mobile NetworksPublication . Mata, Luís; Sousa, Marco; Vieira, Pedro; Queluz, Maria Paula; Rodrigues, AntónioOn the road to the sixth generation of cellular networks (6G), the need to ensure a sustainable usage of natural resources, amid increased competition and cost pressures, has driven the adoption of text Self-Healing Mobile Networks to enhance operational efficiency of current and future wireless networks. This paradigm shift relies on Artificial Intelligence (AI) to increase automation of network functions, notably by applying predictive fault detection and automatic root-cause analysis. In this context, this paper proposes a Deep Learning (DL) model for text self-healing operations based on a Spatial Graph Convolutional Neural Network (SGCN), which is applied to evaluate the performance degradation of Base Stations (BSs) and uncover the underlying root-causes. The advantages of the proposed DL model are threefold. Firstly, it is especially suited for wireless network applications, leveraging the SGCN to account for spatial dependencies among BSs and their physical characteristics. Secondly, the proposed model offers the flexibility to process diverse types of predictive features, including Performance Management (PM), Fault Management (FM), or other data types. Thirdly, it incorporates an explainability module that pinpoints the input features, such as PM counters, with the most significant influence on BS performance, thereby shedding light on its root-cause factors. The proposed model was evaluated on a live 4G network dataset and the results confirmed its effectiveness in identifying BS performance degradation. An F1-score of 89.6% was achieved in the classification of performance failures, which includes a 27% reduction in false negatives compared to prior research outcomes. In a live network environment, this reduction translates into substantial improvements in Quality of Experience (QoE) for the end users and cost savings for the Mobile Network Operators (MNOs).
- Coverage and Data Rate Analysis for a Novel Cell-Sweeping-Based RAN DeploymentPublication . Borralho, Rúben; Quddus, Atta Ul; Mohamed, Abdelrahim; Vieira, Pedro; Tafazolli, RahimAdequate and uniform network coverage provision is one of the main objectives of cellular service providers. Additionally, the densification of cells exacerbates coverage and service provision challenges, particularly at the cell-edges. In this paper, we present a new approach of cell-sweeping-based Base Stations (BSs) deployments in cellular Radio Access Networks (RANs) where the coverage is improved by enhancing the cell-edge performance. In essence, the concept of cell-sweeping rotates/sweeps the sectors of a site in azimuth continuously/discretely resulting in near-uniform distribution of the signal-to-interference-plus-noise ratio (SINR) around the sweeping site. This paper investigates the proposed concept analytically by deriving expressions for the PDF/CDF of SINR and achievable rate; and with the help of system-level simulations, it shows that the proposed concept can provide throughput gains of up to 125% at the cell-edge. Then, using a link-budget analysis, it is shown that the maximum allowable path loss (MAPL) increases by 2.1 dB to 4.1 dB corresponding to the gains in wideband SINR and post-equalized SINR, respectively. This increase in MAPL can be translated to cell-radius/area with the help of the Okumura-Hata propagation model and results in cell-coverage area enhancement by 30% to 66% in a Typical Urban cell deployment scenario.
- Computing RF Tree Distance over Succinct RepresentationsPublication . Branco, António Pedro; Vaz, Cátia; Francisco, Alexandre P.There are several tools available to infer phylogenetic trees, which depict the evolutionary relationships among biological entities such as viral and bacterial strains in infectious outbreaks or cancerous cells in tumor progression trees. These tools rely on several inference methods available to produce phylogenetic trees, with resulting trees not being unique. Thus, methods for comparing phylogenies that are capable of revealing where two phylogenetic trees agree or differ are required. An approach is then proposed to compute a similarity or dissimilarity measure between trees, with the Robinson–Foulds distance being one of the most used, and which can be computed in linear time and space. Nevertheless, given the large and increasing volume of phylogenetic data, phylogenetic trees are becoming very large with hundreds of thousands of leaves. In this context, space requirements become an issue both while computing tree distances and while storing trees. We propose then an efficient implementation of the Robinson–Foulds distance over tree succinct representations. Our implementation also generalizes the Robinson–Foulds distances to labelled phylogenetic trees, i.e., trees containing labels on all nodes, instead of only on leaves. Experimental results show that we are able to still achieve linear time while requiring less space. Our implementation in C++ is available as an open-source tool.
- Grating coupler design for low-cost fabrication in amorphous silicon photonic integrated circuitsPublication . Almeida, Daniel; Lourenço, Paulo; Fantoni, Alessandro; Costa, João; Vieira, ManuelaPhotonic circuits find applications in biomedicine, manufacturing, quantum computing and communications. Photonic waveguides are crucial components, typically having cross-section orders of magnitude inferior when compared with other photonic components (e.g., optical fibers, light sources and photodetectors). Several light-coupling methods exist, consisting of either on-plane (e.g., adiabatic and end-fire coupling) or off-plane methods (e.g., grating and vertical couplers). The grating coupler is a versatile light-transference technique which can be tested at wafer level, not requiring specific fiber terminations or additional optical components, like lenses, polarizers or prisms. This study focuses on fully-etched grating couplers without a bottom reflector, made from hydrogenated amorphous silicon (a-Si:H), deposited over a silica substrate. Different coupler designs were tested, and of these we highlight two: the superimposition of two lithographic masks with different periods and an offset between them to create a random distribution and a technique based on the quadratic refractive-index variation along the device’s length. Results were obtained by 2D-FDTD simulation. The designed grating couplers achieve coupling efficiencies for the TE-like mode over −8 dB (mask overlap) and −3 dB (quadratic variation), at a wavelength of 1550 nm. The coupling scheme considers a 220 nm a-Si:H waveguide and an SMF-28 optical fiber.
- Analog flat-level circuit synthesis with genetic algorithmsPublication . Gomes, Miguel; Tavares, Rui; Goes, JoãoThis paper proposes new techniques for automatic simulation-based analog circuit synthesis using genetic algorithms. This is intended to contribute to the set of electronic design automation tools that use genetic algorithms in circuit synthesis, especially those that use the simulator-in-the-loop paradigm. In this study, a genetic algorithm was employed as the generation engine for analog circuits, and variable-length chromosomes were used to describe circuit topology. The entire process is carried out on a flat level (device level), i.e. using the transistor and other elementary devices (e.g. resistors) as the basic elementary blocks. Circuit synthesis is accomplished without any knowledge of previously defined topologies (or analog block cells). Three techniques are presented for analog circuit synthesis that are incorporated in the genetic algorithm, which contribute to its robustness, leading to better and faster results. These techniques can be summarized as follows: 1) adaptive probability of chromosome acceptance, 2) removal of redundant or useless components, and 3) segmented evolution. The automatic process starts with the circuit input and output specifications and proceeds with the evolution of both circuit topology and component sizing. The results shown in this paper include a 40 dB DC gain amplifier, which, when evaluated with SPECTRE/CADENCE 6.0, using a standard 130 nm technology, with a load capacitor of 10 pF, has a gain of 102 V/V, a GBW product of 70 MHz, and a figure of merit of 1436 MHz.pF/mW.