Algorithms for propagation-aware underwater ranging and localization

Mención Internacional en el título de doctorWhile oceans occupy most of our planet, their exploration and conservation are one of the crucial research problems of modern time. Underwater localization stands among the key issues on the way to the proper inspection and monitoring of this significant part of our world. In this thesis, we investigate and tackle different challenges related to underwater ranging and localization. In particular, we focus on algorithms that consider underwater acoustic channel properties. This group of algorithms utilizes additional information about the environment and its impact on acoustic signal propagation, in order to improve the accuracy of location estimates, or to achieve a reduced complexity, or a reduced amount of resources (e.g., anchor nodes) compared to traditional algorithms. First, we tackle the problem of passive range estimation using the differences in the times of arrival of multipath replicas of a transmitted acoustic signal. This is a costand energy- effective algorithm that can be used for the localization of autonomous underwater vehicles (AUVs), and utilizes information about signal propagation. We study the accuracy of this method in the simplified case of constant sound speed profile (SSP) and compare it to a more realistic case with various non-constant SSP. We also propose an auxiliary quantity called effective sound speed. This quantity, when modeling acoustic propagation via ray models, takes into account the difference between rectilinear and non-rectilinear sound ray paths. According to our evaluation, this offers improved range estimation results with respect to standard algorithms that consider the actual value of the speed of sound. We then propose an algorithm suitable for the non-invasive tracking of AUVs or vocalizing marine animals, using only a single receiver. This algorithm evaluates the underwater acoustic channel impulse response differences induced by a diverse sea bottom profile, and proposes a computationally- and energy-efficient solution for passive localization. Finally, we propose another algorithm to solve the issue of 3D acoustic localization and tracking of marine fauna. To reach the expected degree of accuracy, more sensors are often required than are available in typical commercial off-the-shelf (COTS) phased arrays found, e.g., in ultra short baseline (USBL) systems. Direct combination of multiple COTS arrays may be constrained by array body elements, and lead to breaking the optimal array element spacing, or the desired array layout. Thus, the application of state-of-the-art direction of arrival (DoA) estimation algorithms may not be possible. We propose a solution for passive 3D localization and tracking using a wideband acoustic array of arbitrary shape, and validate the algorithm in multiple experiments, involving both active and passive targets.Part of the research in this thesis has been supported by the EU H2020 program under project SYMBIOSIS (G.A. no. 773753).This work has been supported by IMDEA Networks InstitutePrograma de Doctorado en Ingeniería Telemática por la Universidad Carlos III de MadridPresidente: Paul Daniel Mitchell.- Secretario: Antonio Fernández Anta.- Vocal: Santiago Zazo Bell

Design of an Optimal Testbed for Tracking of Tagged Marine Megafauna

Underwater acoustic technologies are a key component for exploring the behavior of marine megafauna such as sea turtles, sharks, and seals. The animals are marked with acoustic devices (tags) that periodically emit signals encoding the device's ID along with sensor data such as depth, temperature, or the dominant acceleration axis - data that is collected by a network of deployed receivers. In this work, we aim to optimize the locations of receivers for best tracking of acoustically tagged marine megafauna. The outcomes of such tracking allows the evaluation of the animals' motion patterns, their hours of activity, and their social interactions. In particular, we focus on how to determine the receivers' deployment positions to maximize the coverage area in which the tagged animals can be tracked. For example, an overly-condensed deployment may not allow accurate tracking, whereas a sparse one, may lead to a small coverage area due to too few detections. We formalize the question of where to best deploy the receivers as a non-convex constraint optimization problem that takes into account the local environment and the specifications of the tags, and offer a sub-optimal, low-complexity solution that can be applied to large testbeds. Numerical investigation for three stimulated sea environments shows that our proposed method is able to increase the localization coverage area by 30%, and results from a test case experiment demonstrate similar performance in a real sea environment. We share the implementation of our work to help researchers set up their own acoustic observatory.Comment: Submitted for publication in Frontiers in Marine Science, special topic on Tracking Marine Megafauna for Conservation and Marine Spatial Plannin

Wireless Sensor Networks for Underwater Localization: A Survey

Autonomous Underwater Vehicles (AUVs) have widely deployed in marine investigation and ocean exploration in recent years. As the fundamental information, their position information is not only for data validity but also for many real-world applications. Therefore, it is critical for the AUV to have the underwater localization capability. This report is mainly devoted to outline the recent advance- ment of Wireless Sensor Networks (WSN) based underwater localization. Several classic architectures designed for Underwater Acoustic Sensor Network (UASN) are brie y introduced. Acoustic propa- gation and channel models are described and several ranging techniques are then explained. Many state-of-the-art underwater localization algorithms are introduced, followed by the outline of some existing underwater localization systems

A high-performance electromagnetic vibration energy harvester based on ring magnets with Halbach configuration: design, optimization, and applications

Electromagnetic vibration energy harvesting is a relatively modern technology that has received relevant attention in the last decade from the research community and industry as a potential complement or alternative to the inconvenient employment of batteries for powering ultra-low-power devices, microelectromechanical systems, and wireless sensor networks. However, there are still many flaws in this technology that require to be addressed to develop truly practical, reliable, and cost-effective electromagnetic generators, without which industries can still not avoid relying primarily on batteries for powering wireless devices. This dissertation is mainly concerned with developing a high-power, compact, and yet simplified electromagnetic vibration energy harvester capable of reaching high power density levels without the necessity of a complex design, which is generally accompanied by an increment in fabrication costs. For this purpose, a ring-shaped magnet structure consisting of three ring magnets in a linear Halbach configuration is proposed in the present thesis. This particular structure is also compared, in terms of their output performance, with several ring magnet arrangements that include single magnets, double magnet arrays, and an alternative Halbach configuration to determine the actual benefits of the employed Halbach array within the proposed architecture. Also, the coil-magnet parameters of the selected transducer have been further optimized, mainly as a function of the inner radius, the height, and the wire diameter of the coil, to maximize its power generation. Besides, a harvester prototype based on the proposed configuration has been fabricated to validate the modeling strategy used and to certify the reliability of the proposed design regarding its power generation capabilities. The results of the power density normalized to the square of the excitation amplitude obtained for the optimized device and the fabricated prototype are found to be significantly higher than the ones associated with devices described in the literature for similar applications. Furthermore, the proposed electromagnetic generator has been tested and simulated in the framework of two industrial applications to determine its feasibility and output performance: a railway tunnel and a water distribution system. In both cases, the most relevant characteristics of the site under evaluation and the field test setup employed for data acquisition are thoroughly described. The field test measurements and overall results are presented and discussed together with the performance simulations obtained for various scenarios, including different significant natural frequencies of the harvester and several locations of particular interest. Results demonstrate that the applicability of the proposed electromagnetic harvester in the context of underground railway systems is feasible, even for non-usual locations subjected to low vibration amplitudes. Also, for the case of water distribution systems, in which the vibration levels are extremely low, the output performance results of the proposed generator are found promising.La recolección de energía de vibración mediante transductores electromagnéticos es una tecnología relativamente moderna que ha recibido especial atención en la última década por parte de la comunidad científica e industrial como una potencial alternativa al uso de baterías para alimentar dispositivos de ultra baja potencia, sistemas microelectromecánicos y redes de sensores inalámbricos. Sin embargo, existen aún muchas problemáticas en esta tecnología que requieren ser atendidas para poder desarrollar generadores electromagnéticos realmente prácticos, confiables y económicos, necesarios para proveer a la industria de una solución confiable que permita no depender primordialmente de las baterías para alimentar dispositivos inalámbricos. Esta tesis doctoral se enfoca fundamentalmente en el desarrollo de un recolector de energía de vibración mediante transducción electromagnética, de alta potencia, compacto y simplificado, capaz de alcanzar altos niveles de densidad de potencia generada sin la necesidad de un diseño complejo, el cual, generalmente, viene acompañado de un incremento de los costes de fabricación. Para este propósito, esta tesis propone una estructura magnética formada por tres imanes anulares en configuración Halbach lineal. Para determinar los beneficios reales de la configuración Halbach empleada dentro de la arquitectura propuesta, esta estructura en particular se compara, en términos de rendimiento de salida, con varias configuraciones de imanes anulares: un único imán, dos imanes y una configuración Halbach alternativa. Además, los parámetros del sistema bobina-imán del transductor seleccionado han sido optimizados, principalmente en función del radio interno, la altura y el diámetro del cable de la bobina, para maximizar su generación de potencia. Adicionalmente, se ha fabricado un prototipo de recolector de energía basado en la configuración propuesta para validar la estrategia de modelado utilizada y certificar la fiabilidad del diseño propuesto con respecto a su capacidad de generación de energía. Los resultados en términos de densidad de potencia normalizada por cuadrado de la amplitud de excitación, obtenidos para el dispositivo optimizado y el prototipo fabricado, son significativamente más altos que los asociados con dispositivos descritos en la literatura para aplicaciones similares. Finalmente, el generador electromagnético propuesto ha sido probado y simulado en el marco de dos aplicaciones industriales para determinar su aplicabilidad y eficiencia en situaciones reales. Concretamente, la aplicaciones escogidas han sido un túnel ferroviario y un sistema de distribución de agua. En ambos casos, las características más relevantes del emplazamiento de estudio y la configuración de los ensayos de campo desarrollados para la adquisición de datos son descritas minuciosamente. Las medidas de campo y los resultados generales se presentan y discuten junto con las simulaciones de rendimiento de salida obtenidas para distintos escenarios, incluyendo diferentes frecuencias naturales significativas del dispositivo y varias locaciones de particular interés. Los resultados demuestran que la aplicabilidad del recolector de energía de vibración mediante transducción elec-tromagnética propuesto en el contexto de los sistemas ferroviarios subterráneos es factible, incluso para lugares no habituales sujetos a bajas amplitudes de vibración. Para el caso de los sistemas de distribución de agua, aunque los niveles de vibración obtenidos experimetales son extremadamente bajos, los resultados de rendimiento de salida del generador propuesto son prometedores.Postprint (published version

Position estimation in indoor localization with trilateration

Triangulateration uses geometric distance to estimate the location of user by employing techniques like received signal strength (RSS), time-of-arrival (TOA), time-difference-of-arrival (TDOA) and image processing. Radio frequency (RF) signal positioning using TOA or TDOA techniques generally requires timing synchronization of the anchors and/or the anchors and targets. If the desired position accuracy is high and coverage area is large, timing synchronization will be an extremely challenging issue. The first part of this dissertation focuses on improving the performance or deployability of indoor localization systems. Specifically, we propose a synchronization-free positioning network architecture that eliminates the need of timing synchronization. Another problem that remains unsolved in RF based localization is the non-line-of-sight (NLOS) problem, which greatly degrades the positioning performance. We propose a semidefinite programing (SDP) with a soft-minimal method and an NLOS link identification method with bias deduction to mitigate the NLOS error TOA systems. For TDOA systems, NLOS mitigation is more difficult since a reference should be fixed first. To overcome this problem, we propose a method to transform the TDOA architecture into a TOA one, and then form a SDP problem with new constraints. To avoid the special problems and difficulties in RF signal positioning, such as the synchronization and NLOS problems, in the second part of the dissertation, we propose an image-tag based localization using image processing and convolutional neural network (CNN). In the proposed method, after the segmentation of the tag from the image, information such as the tag ID, the distance, and the angle with reference to the camera are retrieved through CNNs. The camera position is finally reliably and accurately estimated from such retrieved information. The proposed method simplifies the system and provide good accuracy compare to RF based system. In addition, the proposed method effectively resolve those issues that exist in the traditional image-based localization, like the high cost, blind spot problems and unreliable and not scalable for in changing environments.Keywords: Convolutional neural network (CNN), Wi-Fi, Image, UWB, Algorithm, Localizatio