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[pt] Neste trabalho de dissertação são propostos algoritmos adaptativos que exploram a esparsidade em redes distribuídas de sensores para estimação de parâmetros e estimação espectral. São desenvolvidos algoritmos gradiente conjugado (CG) distribuído para os protocolos consenso e difusão em versão convencional e modificada (MCG). Esses algoritmos são desenvolvidos com exploração de esparsidade usando as funções penalidades l1 e log-sum. Os métodos propostos apresentam um melhor desempenho en termos de velocidade de convergência e desvio médio quadratico (MSD) que as já conhecidas variantes distribuídas do algoritmo least mean square (LMS) e muito próximo ao desempenho do algoritmo recursive least square (RLS). Além disso, propõe-se um algoritmo distribuído de optimização alternada de variáveis discretas e contínuas (DAMDC) baseado no LMS. O algoritmo DAMDC-LMS apresenta um desempenho muito próximo ao algoritmo oráculo e tem maior velocidade de convergência que os algoritmos estudados com exploração de esparsidade. Os resultados numéricos mostram que o algoritmo DAMDC-LMS pode ser aplicado em vários cenários. / [en] This dissertation proposes distributed adaptive algorithms exploiting sparsity for parameter and spectrum estimation over sensor networks. Conventional and modified conjugate gradient (CG and MCG) algorithms using consensus and diffusion strategies are presented. Sparsity-aware versions of CG an MCG algorithms using l1 and log-sum penalty functions are developed. The proposed sparsity-aware and non-sparse CG and MCG methods outperform the equivalent variants of the least-mean square (LMS) algorithms in terms of convergence rate and mean square deviation (MSD) at steady state, and have a close performance to the recursive least square (RLS) algorithm. The diffusion CG strategies have shown the best performance, specifically the adapt then combine (ATC) version. Furthermore a distributed alternating mixed discretecontinuous (DAMDC) algorithm to approach the oracle algorithm based on the diffusion strategy for parameter and spectrum estimation over sensor networks is proposed. An LMS type algorithm with the DAMDC proposed technique obtains the oracle matrix in an adaptive way and compare it with the existing sparsity-aware as well as the classical algorithms. The proposed algorithm has an improved performance in terms of MSD. Numerical results show that the DAMDC-LMS algorithm is reliable and can be applied in several scenarios.

Structural Health Monitoring (SHM) of automobile tires has been an active area of research in the last few years. Within this area, the monitoring of strain on tires using wireless devices and networks is gaining prominence because these techniques do not require any wired connections. Various tire manufacturers are looking into SHM of automobile tires due to the Transportation Recall Enhancement, Accountability and Documentation (TREAD) act which demands installation of tire pressure monitoring devices within the tire. Besides measuring tire pressures, tire manufactures are also examining ways to measure strain and temperature as well to enhance overall safety of an automobile. A sensor system that can measure the overall strain of a tire is known as a centralized strain sensing system. However, a centralized strain sensing system cannot find the location and severity of the damage on the tire, which is a basic requirement. Various sensors such as acceleration and optical sensors have also been proposed to be used together to get more local damage information on the tire. In this thesis we have developed a strain sensing system that performs local strain measurements on the tire and transmits them to a console inside the vehicle wirelessly. Our sensing system utilizes a new sensing material called Metal RubberTM which is shown to be conductive like metal, and flexible as rubber. Also, we have also developed a reliable and an energy efficient geographic routing protocol for transporting strain data wirelessly from a tire surface to the driver of the automobile. / Master of Science

Yes / A subsurface chamber transceiver system and associated propagation channel link budget considerations for an underground wireless sensor system (UWSS) are presented: the application was a sewerage system for a water utility company. The UWSS operates over the GSM850/900, GSM1800/1900 and UMTS bands in order to operate with the standard public mobile phone system. A novel antenna was developed to minimize path loss from the underground location: a folded loop type, which is small enough to fit conveniently inside a utility manhole access chamber while giving adequate signal strength to link to mobile base stations from such a challenging environment. The electromagnetic performance was simulated and measured in both free space and in a real manhole chamber. An experimental test bed was created to determine the return loss and received signal strength with different transceiver positions below the manhole chamber access cover. Both numerical and experimental results suggested an optimum position of the unit inside the manhole, combining easy access for maintenance with viable received signal strength. This confirmed that the characteristics were adequate for incorporation in a transceiver designed to communicate with mobile base stations from underground. A field trial confirmed the successful operation of the system under severe conditions. / This work was supported partially by Yorkshire Innovation Fund, IETG Ltd. Contract, Research Development Project (RDP) and the European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

2025 / Over the last decade, the application of Wireless Sensor Networks (WSNs) has surged in fields such as environmental monitoring, human health, and smart cities. With this wealth of technologies comes the challenge of how to extract volumes of data collected by such sensor nodes distributed over large, often remote, geographical regions. Data harvesting is the problem of extracting measurements from the remote nodes of WSNs using mobile agents such as ground vehicles or drones. The use of mobile agents can significantly reduce the energy consumption of sensor nodes relative to other modes of extracting the data, extending the lifetime and capabilities of the WSN. Moreover, in remote areas where GPS may not be feasible due to limited power resources on the sensor nodes, the need for accurate sensor node localization and signal broadcasting model estimation becomes critical. Therefore, designing the trajectory of mobile agents is crucial for rapid data collection and information gathering while adhering to vehicle constraints such as dynamics and energy usage. In this thesis, we focus on the application of optimal control methods to design trajectories for mobile agents in data harvesting. This thesis makes contributions in three areas: the creation of a parameterized optimal control policy, the application of a Deep Reinforcement Learning (DRL) based control, and the use of Fisher Information (FI) as a cost matrix in a Receding Horizon Control (RHC) method. Parameterized Optimal Control Policy: Our contributions in this area begin by considering a data harvesting problem in 1-D space. We use a Hamiltonian analysis to show that the optimal control can be described using a parameterized policy and then develop a gradient descent scheme using Infinitesimal Perturbation Analysis (IPA) to calculate the gradients of the cost function with respect to the control parameters. We also consider this problem in a multi-agent setting. To avoid collisions between agents, we apply a Control Barrier Function (CBF) technique to ensure the agents closely track the desired optimal trajectory to complete their mission while avoiding any collisions. Finally, we extend the problem to a mobile sensor scenario. In this more complicated setting we demonstrate that the optimization problem for the control policy parameters can be effectively solved using a heuristic approach. Deep-Reinforcement-Learning based Control: The parametric optimal control approach cannot be easily extended from the 1-D setting to 2-D space. For this reason, we turn to DRL techniques. We utilize Hamiltonian analysis again to get the necessary conditions for optimal control and then translate the problem to a Markov Decision Process (MDP) in discrete time. We apply reinforcement learning techniques, including double deep Q-learning and Proximal Policy Optimization (PPO), to find high-performing solutions across different scenarios. We demonstrate the effectiveness of these methods in 2-D simulations. Fisher-Information-based Receding Horizon Control: For the data harvesting problem in large scale unknown environments, estimating the parameters defining the broadcast model and the location of all the nodes in the environment is critical for efficient extraction of the data. To address that, we start with a Received Signal Strength (RSS) model that relies on a Line-of-Sight (LoS) path-loss model with measurements that are corrupted by Gaussian distributed noise. We first consider a single agent tasked with estimating these unknown parameters in discrete time, and then develop a Fisher Information Matrix (FIM) Receding Horizon (RH) controller for agent motion planning in real time. We also design a Neural Network (NN)-based controller to approximate the optimal solution to the Hamilton-Jacobi-Bellman (HJB) problem, maximizing information gain along a continuous time trajectory. Additionally, a two-stage formation-based RH controller is designed for multi-agent scenarios. The experiments demonstrate that the optimal control policy contribute to the high performance of data collection and the FI-based RHC methods enhance the estimation accuracy in various simulation environments.