3,053 research outputs found

    Medium access control via nearest-neighbor interactions for regular wireless networks

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    A Chemistry-Inspired Framework for Achieving Consensus in Wireless Sensor Networks

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    The aim of this paper is to show how simple interaction mechanisms, inspired by chemical systems, can provide the basic tools to design and analyze a mathematical model for achieving consensus in wireless sensor networks, characterized by balanced directed graphs. The convergence and stability of the model are first proven by using new mathematical tools, which are borrowed directly from chemical theory, and then validated by means of simulation results, for different network topologies and number of sensors. The underlying chemical theory is also used to derive simple interaction rules that may account for practical issues, such as the estimation of the number of neighbors and the robustness against perturbations. Finally, the proposed chemical solution is validated under real-world conditions by means of a four-node hardware implementation where the exchange of information among nodes takes place in a distributed manner (with no need for any admission control and synchronism procedure), simply relying on the transmission of a pulse whose rate is proportional to the state of each sensor.Comment: 12 pages, 10 figures, submitted to IEEE Sensors Journa

    A survey of machine learning techniques applied to self organizing cellular networks

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    In this paper, a survey of the literature of the past fifteen years involving Machine Learning (ML) algorithms applied to self organizing cellular networks is performed. In order for future networks to overcome the current limitations and address the issues of current cellular systems, it is clear that more intelligence needs to be deployed, so that a fully autonomous and flexible network can be enabled. This paper focuses on the learning perspective of Self Organizing Networks (SON) solutions and provides, not only an overview of the most common ML techniques encountered in cellular networks, but also manages to classify each paper in terms of its learning solution, while also giving some examples. The authors also classify each paper in terms of its self-organizing use-case and discuss how each proposed solution performed. In addition, a comparison between the most commonly found ML algorithms in terms of certain SON metrics is performed and general guidelines on when to choose each ML algorithm for each SON function are proposed. Lastly, this work also provides future research directions and new paradigms that the use of more robust and intelligent algorithms, together with data gathered by operators, can bring to the cellular networks domain and fully enable the concept of SON in the near future

    Distributed synchronization algorithms for wireless sensor networks

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    The ability to distribute time and frequency among a large population of interacting agents is of interest for diverse disciplines, inasmuch as it enables to carry out complex cooperative tasks. In a wireless sensor network (WSN), time/frequency synchronization allows the implementation of distributed signal processing and coding techniques, and the realization of coordinated access to the shared wireless medium. Large multi-hop WSN\u27s constitute a new regime for network synchronization, as they call for the development of scalable, fully distributed synchronization algorithms. While most of previous research focused on synchronization at the application layer, this thesis considers synchronization at the lowest layers of the communication protocol stack of a WSN, namely the physical and the medium access control (MAC) layer. At the physical layer, the focus is on the compensation of carrier frequency offsets (CFO), while time synchronization is studied for application at the MAC layer. In both cases, the problem of realizing network-wide synchronization is approached by employing distributed clock control algorithms based on the classical concept of coupled phase and frequency locked loops (PLL and FLL). The analysis takes into account communication, signaling and energy consumption constraints arising in the novel context of multi-hop WSN\u27s. In particular, the robustness of the algorithms is checked against packet collision events, infrequent sync updates, and errors introduced by different noise sources, such as transmission delays and clock frequency instabilities. By observing that WSN\u27s allow for greater flexibility in the design of the synchronization network architecture, this work examines also the relative merits of both peer-to-peer (mutually coupled - MC) and hierarchical (master-slave - MS) architectures. With both MC and MS architectures, synchronization accuracy degrades smoothly with the network size, provided that loop parameters are conveniently chosen. In particular, MS topologies guarantee faster synchronization, but they are hindered by higher noise accumulation, while MC topologies allow for an almost uniform error distribution at the price of much slower convergence. For all the considered cases, synchronization algorithms based on adaptive PLL and FLL designs are shown to provide robust and scalable network-wide time and frequency distribution in a WSN

    SIMULATION AND ANALYSIS OF VEHICULAR AD-HOC NETWORKS IN URBAN AND RURAL AREAS

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    According to the American National Highway Traffic Safety Administration, in 2010, there were an estimated 5,419,000 police-reported traffic crashes, in which 32,885 people were killed and 2,239,000 people were injured in the US alone. Vehicular Ad-Hoc Network (VANET) is an emerging technology which promises to decrease car accidents by providing several safety related services such as blind spot, forward collision and sudden braking ahead warnings. Unfortunately, research of VANET is hindered by the extremely high cost and complexity of field testing. Hence it becomes important to simulate VANET protocols and applications thoroughly before attempting to implement them. This thesis studies the feasibility of common mobility and wireless channel models in VANET simulation and provides a general overview of the currently available VANET simulators and their features. Six different simulation scenarios are performed to evaluate the performance of AODV, DSDV, DSR and OLSR Ad-Hoc routing protocols with UDP and TCP packets. Simulation results indicate that reactive protocols are more robust and suitable for the highly dynamic VANET networks. Furthermore, TCP is found to be more suitable for VANET safety applications due to the high delay and packet drop of UDP packets.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

    Self-organizing Network Optimization via Placement of Additional Nodes

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    Das Hauptforschungsgebiet des Graduiertenkollegs "International Graduate School on Mobile Communication" (GS Mobicom) der Technischen Universität Ilmenau ist die Kommunikation in Katastrophenszenarien. Wegen eines Desasters oder einer Katastrophe können die terrestrischen Elementen der Infrastruktur eines Kommunikationsnetzwerks beschädigt oder komplett zerstört werden. Dennoch spielen verfügbare Kommunikationsnetze eine sehr wichtige Rolle während der Rettungsmaßnahmen, besonders für die Koordinierung der Rettungstruppen und für die Kommunikation zwischen ihren Mitgliedern. Ein solcher Service kann durch ein mobiles Ad-Hoc-Netzwerk (MANET) zur Verfügung gestellt werden. Ein typisches Problem der MANETs ist Netzwerkpartitionierung, welche zur Isolation von verschiedenen Knotengruppen führt. Eine mögliche Lösung dieses Problems ist die Positionierung von zusätzlichen Knoten, welche die Verbindung zwischen den isolierten Partitionen wiederherstellen können. Hauptziele dieser Arbeit sind die Recherche und die Entwicklung von Algorithmen und Methoden zur Positionierung der zusätzlichen Knoten. Der Fokus der Recherche liegt auf Untersuchung der verteilten Algorithmen zur Bestimmung der Positionen für die zusätzlichen Knoten. Die verteilten Algorithmen benutzen nur die Information, welche in einer lokalen Umgebung eines Knotens verfügbar ist, und dadurch entsteht ein selbstorganisierendes System. Jedoch wird das gesamte Netzwerk hier vor allem innerhalb eines ganz speziellen Szenarios - Katastrophenszenario - betrachtet. In einer solchen Situation kann die Information über die Topologie des zu reparierenden Netzwerks im Voraus erfasst werden und soll, natürlich, für die Wiederherstellung mitbenutzt werden. Dank der eventuell verfügbaren zusätzlichen Information können die Positionen für die zusätzlichen Knoten genauer ermittelt werden. Die Arbeit umfasst eine Beschreibung, Implementierungsdetails und eine Evaluierung eines selbstorganisierendes Systems, welche die Netzwerkwiederherstellung in beiden Szenarien ermöglicht.The main research area of the International Graduate School on Mobile Communication (GS Mobicom) at Ilmenau University of Technology is communication in disaster scenarios. Due to a disaster or an accident, the network infrastructure can be damaged or even completely destroyed. However, available communication networks play a vital role during the rescue activities especially for the coordination of the rescue teams and for the communication between their members. Such a communication service can be provided by a Mobile Ad-Hoc Network (MANET). One of the typical problems of a MANET is network partitioning, when separate groups of nodes become isolated from each other. One possible solution for this problem is the placement of additional nodes in order to reconstruct the communication links between isolated network partitions. The primary goal of this work is the research and development of algorithms and methods for the placement of additional nodes. The focus of this research lies on the investigation of distributed algorithms for the placement of additional nodes, which use only the information from the nodes’ local environment and thus form a self-organizing system. However, during the usage specifics of the system in a disaster scenario, global information about the topology of the network to be recovered can be known or collected in advance. In this case, it is of course reasonable to use this information in order to calculate the placement positions more precisely. The work provides the description, the implementation details and the evaluation of a self-organizing system which is able to recover from network partitioning in both situations

    Distributed field estimation in wireless sensor networks

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    This work takes into account the problem of distributed estimation of a physical field of interest through a wireless sesnor networks
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