4 research outputs found

    Underwater Wireless Communications for Cooperative Robotics with UWSim-NET

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    The increasing number of autonomous underwater vehicles (AUVs) cooperating in underwater operations has motivated the use of wireless communications. Their modeling can minimize the impact of their limited performance in real-time robotic interventions. However, robotic frameworks hardly ever consider the communications, and network simulators are not suitable for HIL experiments. In this work, the UWSim-NET is presented, an open source tool to simulate the impact of communications in underwater robotics. It gathers the benefits of NS3 in modeling communication networks with those of the underwater robot simulator (UWSim) and the robot operating system (ROS) in modeling robotic systems. This article also shows the results of three experiments that demonstrate the capabilities of UWSim-NET in modeling radio frequency (RF) and acoustic links in underwater scenarios. It also permits evaluating several MAC protocols such as additive links online Hawaii area (ALOHA), slotted floor acquisition multiple access (S-FAMA) and user defined protocols. A third experiment demonstrated the excellent capabilities of UWSim-NET in conducting hardware in the loop (HIL) experiments

    Planificaciones TDMA óptimas en redes submarinas de comunicación

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    Fecha de Lectura de Tesis: 27 de junio de 2018.La necesidad de monitorización de parámetros medioambientales como el nivel de ozono en la atmósfera o la polución en las grandes ciudades entre otros casos, es un hecho probado. La pronta disponibilidad de tales medidas permite poner en marcha acciones correctivas que eviten de otro modo consecuencias irreversibles. La vía principal de obtención de estas mediciones, reside en la aplicación de la tecnología (mediciones in situ, globos sonda, imágenes satélite, etc). Esta situación es trasladable al medio marino, donde hay un interés creciente en estudiar cuál es el efecto global de alteraciones en su estado. Un caso conocido es la variación de las corrientes oceánicas, que tiene un gran impacto en el clima (inundaciones, sequías, etc). En otros casos, esta medición permite responder a emergencias ante desastres naturales, como la detección de tsunamis en un maremoto mediante una red de boyas de flotación. En aguas costeras, también son muchas las aplicaciones que pueden beneficiarse de una medición automatizada de parámetros del agua, entre otros el control de vertidos contaminantes o la monitorización de sedimentos aportados en los estuarios de los ríos, en ambos casos con efectos sobre el equilibrio del ecosistema marino. Una solución cada vez más extendida para obtener medidas continuas en el medio marino, es establecer una red de nodos submarina, donde cada nodo contiene diferentes sensores además de un módem para transmitir y recibir datos. Para recoger los datos medidos, se establece un patrón de comunicaciones entre nodos que haga llegar la información de todos ellos a un nodo especial recolector, para su posterior recogida y procesamiento. La principal dificultad radica en la comunicación inalámbrica entre los nodos, pues el medio marino es muy agresivo e impone serias limitaciones a la propagación de las señales no guiadas, atenuando la onda (más cuanto mayor sea la frecuencia) e imponiendo una baja velocidad de propagación

    Self-organizing Fast Routing Protocols for Underwater Acoustic Communications Networks

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    To address this problem, in this thesis we propose a cross-layer proactive routing initialization mechanism that does not require additional measurements and, at the same time, is energy efficient. Two routing protocols are proposed: Self-Organized Fast Routing Protocol for Radial Underwater Networks (SOFRP) for radial topology and Self-organized Proactive Routing Protocol for Non-uniformly Deployed Underwater Networks (SPRINT) for a randomly deployed network. SOFRP is based on the algorithm to recreate a radial topology with a gateway node, such that packets always use the shortest possible path from source to sink, thus minimizing consumed energy. Collisions are avoided as much as possible during the path initialization. The algorithm is suitable for 2D or 3D areas, and automatically adapts to a varying number of nodes. In SPRINT the routing path to the gateway is formed on the basis of the distance, measured by the signal strength received. The data sending node prefers to choose the neighbor node which is closest to it. It is designed to achieve high data throughput and low energy consumption of the nodes. There is a tradeoff between the throughput and the energy consumption: more distance needs more transmission energy, and more relay nodes (hops) to the destination node affects the throughput. Each hop increases the packet delay and decreases the throughput. Hence, energy consumption requires nearest nodes to be chosen as forwarding node whereas the throughput requires farthest node to be selected to minimize the number of hops. Fecha de lectura de Tesis Doctoral: 11 mayo 2020Underwater Wireless Sensor Networks (UWSNs) constitute an emerging technology for marine surveillance, natural disaster alert and environmental monitoring. Unlike terrestrial Wireless Sensor Networks (WSNs), electromagnetic waves cannot propagate more than few meters in water (high absorption rate). However, acoustic waves can travel long distances in underwater. Therefore, acoustic waves are preferred for underwater communications, but they travel very slow compare to EM waves (typical speed in water is 1500 m/s against 2x10^8 m/s for EM waves). This physical effect makes a high propagation delay and cannot be avoided, but the end-to-end packet delay it can be reduced. Routing delay is one of the major factors in end-to-end packet delay. In reactive routing protocols, when a packet arrives to a node, the node takes some time to select the node to which the data packet would be forwarded. We may reduce the routing delay for time-critical applications by using proactive routing protocols. Other two critical issues in UWSNs are determining the position of the nodes and time synchronization. Wireless sensor nodes need to determine the position of the surrounding nodes to select the next node in the path to reach the sink node. A Global Navigation Satellite System (GNSS) cannot be used because of the very short underwater range of the GNSS signal. Timestamping to estimate the distance is possible but the limited mobility of the UWSN nodes and variation in the propagation speed of the acoustic waves make the time synchronization a challenging task. For these reasons, terrestrial WSN protocols cannot be readily used for underwater acoustic networks

    Modelling, Simulation and Data Analysis in Acoustical Problems

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    Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years
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