Swarm intelligence techniques for optimization and management tasks insensor networks

The main contributions of this thesis are located in the domain of wireless sensor netorks. More in detail, we introduce energyaware algorithms and protocols in the context of the following topics: self-synchronized duty-cycling in networks with energy harvesting capabilities, distributed graph coloring and minimum energy broadcasting with realistic antennas. In the following, we review the research conducted in each case. We propose a self-synchronized duty-cycling mechanism for sensor networks. This mechanism is based on the working and resting phases of natural ant colonies, which show self-synchronized activity phases. The main goal of duty-cycling methods is to save energy by efficiently alternating between different states. In the case at hand, we considered two different states: the sleep state, where communications are not possible and energy consumption is low; and the active state, where communication result in a higher energy consumption. In order to test the model, we conducted an extensive experimentation with synchronous simulations on mobile networks and static networks, and also considering asynchronous networks. Later, we extended this work by assuming a broader point of view and including a comprehensive study of the parameters. In addition, thanks to a collaboration with the Technical University of Braunschweig, we were able to test our algorithm in the real sensor network simulator Shawn (http://shawn.sf.net). The second part of this thesis is devoted to the desynchronization of wireless sensor nodes and its application to the distributed graph coloring problem. In particular, our research is inspired by the calling behavior of Japanese tree frogs, whose males use their calls to attract females. Interestingly, as female frogs are only able to correctly localize the male frogs when their calls are not too close in time, groups of males that are located nearby each other desynchronize their calls. Based on a model of this behavior from the literature, we propose a novel algorithm with applications to the field of sensor networks. More in detail, we analyzed the ability of the algorithm to desynchronize neighboring nodes. Furthermore, we considered extensions of the original model, hereby improving its desynchronization capabilities.To illustrate the potential benefits of desynchronized networks, we then focused on distributed graph coloring. Later, we analyzed the algorithm more extensively and show its performance on a larger set of benchmark instances. The classical minimum energy broadcast (MEB) problem in wireless ad hoc networks, which is well-studied in the scientific literature, considers an antenna model that allows the adjustment of the transmission power to any desired real value from zero up to the maximum transmission power level. However, when specifically considering sensor networks, a look at the currently available hardware shows that this antenna model is not very realistic. In this work we re-formulate the MEB problem for an antenna model that is realistic for sensor networks. In this antenna model transmission power levels are chosen from a finite set of possible ones. A further contribution concerns the adaptation of an ant colony optimization algorithm --currently being the state of the art for the classical MEB problem-- to the more realistic problem version, the so-called minimum energy broadcast problem with realistic antennas (MEBRA). The obtained results show that the advantage of ant colony optimization over classical heuristics even grows when the number of possible transmission power levels decreases. Finally we build a distributed version of the algorithm, which also compares quite favorably against centralized heuristics from the literature.Las principles contribuciones de esta tesis se encuentran en el domino de las redes de sensores inalámbricas. Más en detalle, introducimos algoritmos y protocolos que intentan minimizar el consumo energético para los siguientes problemas: gestión autosincronizada de encendido y apagado de sensores con capacidad para obtener energía del ambiente, coloreado de grafos distribuido y broadcasting de consumo mínimo en entornos con antenas reales. En primer lugar, proponemos un sistema capaz de autosincronizar los ciclos de encendido y apagado de los nodos de una red de sensores. El mecanismo está basado en las fases de trabajo y reposo de las colonias de hormigas tal y como estas pueden observarse en la naturaleza, es decir, con fases de actividad autosincronizadas. El principal objectivo de este tipo de técnicas es ahorrar energía gracias a alternar estados de forma eficiente. En este caso en concreto, consideramos dos estados diferentes: el estado dormido, en el que los nodos no pueden comunicarse y el consumo energético es bajo; y el estado activo, en el que las comunicaciones propician un consumo energético elevado. Con el objetivo de probar el modelo, se ha llevado a cabo una extensa experimentación que incluye tanto simulaciones síncronas en redes móviles y estáticas, como simulaciones en redes asíncronas. Además, este trabajo se extendió asumiendo un punto de vista más amplio e incluyendo un detallado estudio de los parámetros del algoritmo. Finalmente, gracias a la colaboración con la Technical University of Braunschweig, tuvimos la oportunidad de probar el mecanismo en el simulador realista de redes de sensores, Shawn (http://shawn.sf.net). La segunda parte de esta tesis está dedicada a la desincronización de nodos en redes de sensores y a su aplicación al problema del coloreado de grafos de forma distribuida. En particular, nuestra investigación está inspirada por el canto de las ranas de árbol japonesas, cuyos machos utilizan su canto para atraer a las hembras. Resulta interesante que debido a que las hembras solo son capaces de localizar las ranas macho cuando sus cantos no están demasiado cerca en el tiempo, los grupos de machos que se hallan en una misma región desincronizan sus cantos. Basado en un modelo de este comportamiento que se encuentra en la literatura, proponemos un nuevo algoritmo con aplicaciones al campo de las redes de sensores. Más en detalle, analizamos la habilidad del algoritmo para desincronizar nodos vecinos. Además, consideramos extensiones del modelo original, mejorando su capacidad de desincronización. Para ilustrar los potenciales beneficios de las redes desincronizadas, nos centramos en el problema del coloreado de grafos distribuido que tiene relación con diferentes tareas habituales en redes de sensores. El clásico problema del broadcasting de consumo mínimo en redes ad hoc ha sido bien estudiado en la literatura. El problema considera un modelo de antena que permite transmitir a cualquier potencia elegida (hasta un máximo establecido por el dispositivo). Sin embargo, cuando se trabaja de forma específica con redes de sensores, un vistazo al hardware actualmente disponible muestra que este modelo de antena no es demasiado realista. En este trabajo reformulamos el problema para el modelo de antena más habitual en redes de sensores. En este modelo, los niveles de potencia de transmisión se eligen de un conjunto finito de posibilidades. La siguiente contribución consiste en en la adaptación de un algoritmo de optimización por colonias de hormigas a la versión más realista del problema, también conocida como broadcasting de consumo mínimo con antenas realistas. Los resultados obtenidos muestran que la ventaja de este método sobre heurísticas clásicas incluso crece cuando el número de posibles potencias de transmisión decrece. Además, se ha presentado una versión distribuida del algoritmo, que también se compara de forma bastante favorable contra las heurísticas centralizadas conocidas

Tutorizando el aprendizaje proactivo de nuevas tecnologías: taller de programación Android

Mediante el Programa Google EMEA’s AndroidEDU, la UPC ha impartido un novedoso taller de programación para Android. Durante diez semanas se tratan diferentes temas sobre este sistema y una veintena de alumnos trabajan ejercicios en grupos reducidos. Los grupos colaboran para investigar y solucionar las dificultades técnicas que surgen. Posteriormente, cada grupo realiza y defiende un proyecto propio. El interés en Android ha permitido fomentar el aprendizaje proactivo, con muy buenos resultados. Como profesores esta experiencia nos ha permitido afrontar nuevos retos docentes, obligándonos a replantear nuestro rol, a crear material docente adecuado a los nuevos medios de difusión social (foro FIB, YouTube, etc.), y a suplir la falta de experiencia en el tema con una interesante colaboración profesoralumno.SUMMARY: Within the AndroidEDU Google EMEA Program, the UPC has organized a innovative programming workshop for Android. For ten weeks, twenty students (who are organized in small groups) deal with different topics about Android. Those groups work together to investigate and resolve technical difficulties that may arise. By the end of the course, each group works on and fends for its own project.The growing interest in Android has allowed us to apply proactive learning techniques with very good results. As teachers, this experience has allowed us to meet new challenges, since it has forced us to rethink our role, to create educational material accordant with the new communication media (forum FIB, YouTube, etc.), and to supply the lack of expertise with an interesting collaboration between teachers and students.Peer Reviewe

Self-synchronized duty-cycling for mobile sensor networks with energy harvesting capabilities: A swarm intelligence study

When asked if ants rest or if they work untiringly all day long, most people would probably respond that they had no idea. In fact, when watching the bustling life of an ant hill it is hard to imagine that ants take a rest from now and then. However, biologists discovered that ants rest quite a large fraction of their time. Surprisingly, not only single ants show alternate phases of resting and being active, but whole ant colonies exhibit synchronized activity phases that result from self-organization. Inspired by this self-synchronization behaviour of ant colonies, we develop a mechanism for self-synchronized duty-cycling in mobile sensor networks. In addition, we equip sensor nodes with energy harvesting capabilities such as, for example, solar cells. We show that the self-synchronization mechanism can be made adaptive depending on the available energy.Postprint (published version

Tutorizando el aprendizaje proactivo de nuevas tecnologías: taller de programación Android

Mediante el Programa Google EMEA’s AndroidEDU, la UPC ha impartido un novedoso taller de programación para Android. Durante diez semanas se tratan diferentes temas sobre este sistema y una veintena de alumnos trabajan ejercicios en grupos reducidos. Los grupos colaboran para investigar y solucionar las dificultades técnicas que surgen. Posteriormente, cada grupo realiza y defiende un proyecto propio. El interés en Android ha permitido fomentar el aprendizaje proactivo, con muy buenos resultados. Como profesores esta experiencia nos ha permitido afrontar nuevos retos docentes, obligándonos a replantear nuestro rol, a crear material docente adecuado a los nuevos medios de difusión social (foro FIB, YouTube, etc.), y a suplir la falta de experiencia en el tema con una interesante colaboración profesor-alumno

Ant colony optimization for broadcasting in sensor networks under a realistic antenna model

Most, if not all, works from the literature dealing with minimum energy broadcasting in wireless ad-hoc networks such as sensor networks consider antenna models that allow the adjustment of the emission power to any desired real value from zero up to the maximum sensing range. However, looking at the currently available hardware shows that these antenna models are not very realistic. In this work we therefore adapt the currently best available algorithm for minimum energy broadcasting for a more realistic antenna model which only offers few different levels of emission power. The obtained results show that this ant colony optimization algorithm performs well in comparison to a standard heuristic known from the literature.Peer ReviewedPostprint (published version

Foundations of ANTCYCLE: self-synchronized duty-cycling in mobile sensor networks

Ants are generally believed to follow an intensive work routine. Numerous tales and fables refer to ants as conscientious workers. Nevertheless, biologists have discovered that ants also rest for extended periods of time. This does not only hold for individual ants. Interestingly, ant colonies exhibit synchronized activity phases that result from self-organization. In this work, self-synchronization in ant colonies is taken as the inspiring source for a new mechanism of self-synchronized duty-cycling in mobile sensor networks. Hereby, we assume that sensor nodes are equipped with energy harvesting capabilities such as, for example, solar cells. We show that the proposed self-synchronization mechanism can be made adaptive depending on variable energy resources. The main objective of this paper is to study and explore the swarm intelligence foundations of self-synchronized dutycycling. With this purpose in mind, physical constraints such as packet collisions and packet loss are generally not considered.Peer Reviewe

Distributed graph coloring in wireless ad hoc networks: a light-weight algorithm based on Japanese tree frogs' calling behaviour

Wireless and Mobile Networking Conference (WMNC’11) Best Paper AwardGraph coloring concerns the problem of assigning colors to the nodes of a graph such that adjacent nodes do not share the same color. In this paper we deal with the problem of finding valid colorings of graphs in a distributed manner, while minimizing the number of used colors. This problem is at the heart of several problems arising in wireless ad hoc networks. Examples are TDMA slot assignment, wakeup scheduling, and data collection. The proposed algorithm is inspired by the de-synchronization that can be observed in the calling behaviour of male Japanese tree frogs. Experimental results show that our algorithm is very competitive with current state-of-the-art approaches.Peer ReviewedAward-winnin

Distributed graph coloring in wireless ad hoc networks: a light-weight algorithm based on Japanese tree frogs' calling behaviour

Wireless and Mobile Networking Conference (WMNC’11) Best Paper AwardGraph coloring concerns the problem of assigning colors to the nodes of a graph such that adjacent nodes do not share the same color. In this paper we deal with the problem of finding valid colorings of graphs in a distributed manner, while minimizing the number of used colors. This problem is at the heart of several problems arising in wireless ad hoc networks. Examples are TDMA slot assignment, wakeup scheduling, and data collection. The proposed algorithm is inspired by the de-synchronization that can be observed in the calling behaviour of male Japanese tree frogs. Experimental results show that our algorithm is very competitive with current state-of-the-art approaches.Peer ReviewedAward-winnin