Strengths and Weaknesses of Prominent Data Dissemination Techniques in Wireless Sensor Networks

Data dissemination is the most significant task in a Wireless Sensor Network (WSN). From the bootstrapping stage to the full functioning stage, a WSN must disseminate data in various patterns like from the sink to node, from node to sink, from node to node, or the like. This is what a WSN is deployed for. Hence, this issue comes with various data routing models and often there are different types of network settings that influence the way of data collection and/or distribution. Considering the importance of this issue, in this paper, we present a survey on various prominent data dissemination techniques in such network. Our classification of the existing works is based on two main parameters: the number of sink (single or multiple) and the nature of its movement (static or mobile). Under these categories, we have analyzed various previous works for their relative strengths and weaknesses. A comparison is also made based on the operational methods of various data dissemination schemes

Energy-efficient mobile sink routing scheme for clustered corona-based wireless sensor networks

Wireless Sensor Networks (WSNs) are generally composed of several tiny, inexpensive and self-configured sensor nodes, which are able to communicate with each other via wireless communication devices. The main duty of the nodes is to sense data and transmit to a sink via multi- or single-hop data transmission manners. Since the sensor nodes generally are limited in power resources, they deplete their energy rapidly. In addition, sensor nodes are usually distributed in places, where may be too harsh to be accessible for human. Consequently, exchanging or recharging the power supplies of the sensor nodes is difficult. Therefore, energy efficiency is the most critical issue in design of WSN, which affects the lifetime and performance of the network. Several cluster-based schemes are proposed to enhance the energy efficiency; however, most of them generate sub-optimal clusters without considering both coverage and energy issues simultaneously. Furthermore, several mobility-based schemes are proposed in order to achieve balanced energy consumption through optimizing the sojourn time and sojourn location of Mobile Sinks (MS). Nevertheless, most of them adjust the sojourn time of MS under predictable mobility pattern. Moreover, in most of existing mobility based schemes, time limitation is not considered for optimizing the sojourn location of MS. The aim behind this research is to develop an Energy-efficient Mobile Sink Routing (EMSR) Scheme, which improves the energy efficiency. The EMSR is the incorporation of three schemes: Energyefficient based Unequal-sized Clustering (EUC) mechanism aims to construct the optimal sized clusters, which ensures the energy conservation and coverage preservation. Collaborative Mobile Sink-based Inter-Cluster Routing (CMSICR) mechanism aims to optimize the sojourn time of MS to balance the energy consumption among Cluster Heads (CH). An Energy-efficient Intra-cluster Movement of Mobile Sink (EIM2S) mechanism, which identifies the optimal sojourn locations of the MS within clusters in order to balance the energy consumption among Member Nodes (MN). The EMSR partitions the network field into optimal clusters and employs MSs in order to balance the energy consumption among CHs and MNs. Simulation results show that EMSR achieved improved performance in terms of network lifetime by 51%, total energy consumption by 28% wasted energy by 36% compared to existing schemes. In conclusion, the proposed routing scheme proves to be a viable solution for multi hop cluster based WSN

QoS BASED ENERGY EFFICIENT ROUTING IN WIRELESS SENSOR NETWORK

A Wireless Sensor Networks (WSN) is composed of a large number of low-powered sensor nodes that are randomly deployed to collect environmental data. In a WSN, because of energy scarceness, energy efficient gathering of sensed information is one of the most critical issues. Thus, most of the WSN routing protocols found in the literature have considered energy awareness as a key design issue. Factors like throughput, latency and delay are not considered as critical issues in these protocols. However, emerging WSN applications that involve multimedia and imagining sensors require end-to-end delay within acceptable limits. Hence, in addition to energy efficiency, the parameters (delay, packet loss ratio, throughput and coverage) have now become issues of primary concern. Such performance metrics are usually referred to as the Quality of Service (QoS) in communication systems. Therefore, to have efficient use of a sensor node’s energy, and the ability to transmit the imaging and multimedia data in a timely manner, requires both a QoS based and energy efficient routing protocol. In this research work, a QoS based energy efficient routing protocol for WSN is proposed. To achieve QoS based energy efficient routing, three protocols are proposed, namely the QoS based Energy Efficient Clustering (QoSEC) for a WSN, the QoS based Energy Efficient Sleep/Wake Scheduling (QoSES) for a WSN, and the QoS based Energy Efficient Mobile Sink (QoSEM) based Routing for a Clustered WSN. Firstly, in the QoSEC, to achieve energy efficiency and to prolong network/coverage lifetime, some nodes with additional energy resources, termed as super-nodes, in addition to normal capability nodes, are deployed. Multi-hierarchy clustering is done by having super-nodes (acting as a local sink) at the top tier, cluster head (normal node) at the middle tier, and cluster member (normal node) at the lowest tier in the hierarchy. Clustering within normal sensor nodes is done by optimizing the network/coverage lifetime through a cluster-head-selection algorithm and a sleep/wake scheduling algorithm. QoSEC resolves the hot spot problem and prolongs network/coverage lifetime. Secondly, the QoSES addressed the delay-minimization problem in sleep/wake scheduling for event-driven sensor networks for delay-sensitive applications. For this purpose, QoSES assigns different sleep/wake intervals (longer wake interval) to potential overloaded nodes, according to their varied traffic load requirement defined a) by node position in the network, b) by node topological importance, and c) by handling burst traffic in the proximity of the event occurrence node. Using these heuristics, QoSES minimizes the congestion at nodes having heavy traffic loads and ultimately reduces end-to-end delay while maximizing the throughput. Lastly, the QoSEM addresses hot spot problem, delay minimization, and QoS assurance. To address hot-spot problem, mobile sink is used, that move in the network to gather data by virtue of which nodes near to the mobile sink changes with each movement, consequently hot spot problem is minimized. To achieve delay minimization, static sink is used in addition to the mobile sink. Delay sensitive data is forwarded to the static sink, while the delay tolerant data is sent through the mobile sink. For QoS assurance, incoming traffic is divided into different traffic classes and each traffic class is assigned different priority based on their QoS requirement (bandwidth, delay) determine by its message type and content. Furthermore, to minimize delay in mobile sink data gathering, the mobile sink is moved throughout the network based on the priority messages at the nodes. Using these heuristics, QoSEM incur less end-to-end delay, is energy efficient, as well as being able to ensure QoS. Simulations are carried out to evaluate the performance of the proposed protocols of QoSEC, QoSES and QoSEM, by comparing their performance with the established contemporary protocols. Simulation results have demonstrated that when compared with contemporary protocols, each of the proposed protocol significantly prolong the network and coverage lifetime, as well as improve the other QoS routing parameters, such as delay, packet loss ratio, and throughput

Enabling Cyber Physical Systems with Wireless Sensor Networking Technologies

[[abstract]]Over the last few years, we have witnessed a growing interest in Cyber Physical Systems (CPSs) that rely on a strong synergy between computational and physical components. CPSs are expected to have a tremendous impact on many critical sectors (such as energy, manufacturing, healthcare, transportation, aerospace, etc) of the economy. CPSs have the ability to transform the way human-to-human, human-toobject, and object-to-object interactions take place in the physical and virtual worlds. The increasing pervasiveness of Wireless Sensor Networking (WSN) technologies in many applications make them an important component of emerging CPS designs. We present some of the most important design requirements of CPS architectures. We discuss key sensor network characteristics that can be leveraged in CPS designs. In addition, we also review a few well-known CPS application domains that depend on WSNs in their design architectures and implementations. Finally, we present some of the challenges that still need to be addressed to enable seamless integration of WSN with CPS designs.[[incitationindex]]SCI[[booktype]]紙

QoS BASED ENERGY EFFICIENT ROUTING IN WIRELESS SENSOR NETWORK

A Wireless Sensor Networks (WSN) is composed of a large number of low-powered sensor nodes that are randomly deployed to collect environmental data. In a WSN, because of energy scarceness, energy efficient gathering of sensed information is one of the most critical issues. Thus, most of the WSN routing protocols found in the literature have considered energy awareness as a key design issue. Factors like throughput, latency and delay are not considered as critical issues in these protocols. However, emerging WSN applications that involve multimedia and imagining sensors require end-to-end delay within acceptable limits. Hence, in addition to energy efficiency, the parameters (delay, packet loss ratio, throughput and coverage) have now become issues of primary concern. Such performance metrics are usually referred to as the Quality of Service (QoS) in communication systems. Therefore, to have efficient use of a sensor node’s energy, and the ability to transmit the imaging and multimedia data in a timely manner, requires both a QoS based and energy efficient routing protocol. In this research work, a QoS based energy efficient routing protocol for WSN is proposed. To achieve QoS based energy efficient routing, three protocols are proposed, namely the QoS based Energy Efficient Clustering (QoSEC) for a WSN, the QoS based Energy Efficient Sleep/Wake Scheduling (QoSES) for a WSN, and the QoS based Energy Efficient Mobile Sink (QoSEM) based Routing for a Clustered WSN. Firstly, in the QoSEC, to achieve energy efficiency and to prolong network/coverage lifetime, some nodes with additional energy resources, termed as super-nodes, in addition to normal capability nodes, are deployed. Multi-hierarchy clustering is done by having super-nodes (acting as a local sink) at the top tier, cluster head (normal node) at the middle tier, and cluster member (normal node) at the lowest tier in the hierarchy. Clustering within normal sensor nodes is done by optimizing the network/coverage lifetime through a cluster-head-selection algorithm and a sleep/wake scheduling algorithm. QoSEC resolves the hot spot problem and prolongs network/coverage lifetime. Secondly, the QoSES addressed the delay-minimization problem in sleep/wake scheduling for event-driven sensor networks for delay-sensitive applications. For this purpose, QoSES assigns different sleep/wake intervals (longer wake interval) to potential overloaded nodes, according to their varied traffic load requirement defined a) by node position in the network, b) by node topological importance, and c) by handling burst traffic in the proximity of the event occurrence node. Using these heuristics, QoSES minimizes the congestion at nodes having heavy traffic loads and ultimately reduces end-to-end delay while maximizing the throughput. Lastly, the QoSEM addresses hot spot problem, delay minimization, and QoS assurance. To address hot-spot problem, mobile sink is used, that move in the network to gather data by virtue of which nodes near to the mobile sink changes with each movement, consequently hot spot problem is minimized. To achieve delay minimization, static sink is used in addition to the mobile sink. Delay sensitive data is forwarded to the static sink, while the delay tolerant data is sent through the mobile sink. For QoS assurance, incoming traffic is divided into different traffic classes and each traffic class is assigned different priority based on their QoS requirement (bandwidth, delay) determine by its message type and content. Furthermore, to minimize delay in mobile sink data gathering, the mobile sink is moved throughout the network based on the priority messages at the nodes. Using these heuristics, QoSEM incur less end-to-end delay, is energy efficient, as well as being able to ensure QoS. Simulations are carried out to evaluate the performance of the proposed protocols of QoSEC, QoSES and QoSEM, by comparing their performance with the established contemporary protocols. Simulation results have demonstrated that when compared with contemporary protocols, each of the proposed protocol significantly prolong the network and coverage lifetime, as well as improve the other QoS routing parameters, such as delay, packet loss ratio, and throughput

Opportunistic data collection and routing in segmented wireless sensor networks

La surveillance régulière des opérations dans les aires de manoeuvre (voies de circulation et pistes) et aires de stationnement d'un aéroport est une tâche cruciale pour son fonctionnement. Les stratégies utilisées à cette fin visent à permettre la mesure des variables environnementales, l'identification des débris (FOD) et l'enregistrement des statistiques d'utilisation de diverses sections de la surface. Selon un groupe de gestionnaires et contrôleurs d'aéroport interrogés, cette surveillance est un privilège des grands aéroports en raison des coûts élevés d'acquisition, d'installation et de maintenance des technologies existantes. Les moyens et petits aéroports se limitent généralement à la surveillance de quelques variables environnementales et des FOD effectuée visuellement par l'homme. Cette dernière activité impose l'arrêt du fonctionnement des pistes pendant l'inspection. Dans cette thèse, nous proposons une solution alternative basée sur les réseaux de capteurs sans fil (WSN) qui, contrairement aux autres méthodes, combinent les propriétés de faible coût d'installation et maintenance, de déploiement rapide, d'évolutivité tout en permettant d'effectuer des mesures sans interférer avec le fonctionnement de l'aéroport. En raison de la superficie d'un aéroport et de la difficulté de placer des capteurs sur des zones de transit, le WSN se composerait d'une collection de sous-réseaux isolés les uns des autres et du puits. Pour gérer cette segmentation, notre proposition s'appuie sur l'utilisation opportuniste des véhicules circulants dans l'aéroport considérés alors comme un type spécial de nœud appelé Mobile Ubiquitous LAN Extension (MULE) chargé de collecter les données des sous-réseaux le long de son trajet et de les transférer vers le puits. L'une des exigences pour le déploiement d'un nouveau système dans un aéroport est qu'il cause peu ou pas d'interruption des opérations régulières. C'est pourquoi l'utilisation d'une approche opportuniste basé sur des MULE est privilégiée dans cette thèse. Par opportuniste, nous nous référons au fait que le rôle de MULE est joué par certains des véhicules déjà existants dans un aéroport et effectuant leurs déplacements normaux. Et certains nœuds des sous- réseaux exploiteront tout moment de contact avec eux pour leur transmettre les données à transférer ensuite au puits. Une caractéristique des MULEs dans notre application est qu'elles ont des trajectoires structurées (suivant les voies de circulation dans l'aéroport), en ayant éventuellement un contact avec l'ensemble des nœuds situés le long de leur trajet (appelés sous-puits). Ceci implique la nécessité de définir une stratégie de routage dans chaque sous-réseau, capable d'acheminer les données collectées des nœuds vers les sous-puits et de répartir les paquets de données entre eux afin que le temps en contact avec la MULE soit utilisé le plus efficacement possible. Dans cette thèse, nous proposons un protocole de routage remplissant ces fonctions. Le protocole proposé est nommé ACME (ACO-based routing protocol for MULE-assisted WSNs). Il est basé sur la technique d'Optimisation par Colonies de Fourmis. ACME permet d'assigner des nœuds à des sous-puits puis de définir les chemins entre eux, en tenant compte de la minimisation de la somme des longueurs de ces chemins, de l'équilibrage de la quantité de paquets stockés par les sous-puits et du nombre total de retransmissions. Le problème est défini comme une tâche d'optimisation multi-objectif qui est résolue de manière distribuée sur la base des actions des nœuds dans un schéma collaboratif. Nous avons développé un environnement de simulation et effectué des campagnes de calculs dans OMNeT++ qui montrent les avantages de notre protocole en termes de performances et sa capacité à s'adapter à une grande variété de topologies de réseaux.The regular monitoring of operations in both movement areas (taxiways and runways) and non-movement areas (aprons and aircraft parking spots) of an airport, is a critical task for its functioning. The set of strategies used for this purpose include the measurement of environmental variables, the identification of foreign object debris (FOD), and the record of statistics of usage for diverse sections of the surface. According to a group of airport managers and controllers interviewed by us, the wide monitoring of most of these variables is a privilege of big airports due to the high acquisition, installation and maintenance costs of most common technologies. Due to this limitation, smaller airports often limit themselves to the monitoring of environmental variables at some few spatial points and the tracking of FOD performed by humans. This last activity requires stopping the functioning of the runways while the inspection is conducted. In this thesis, we propose an alternative solution based on Wireless Sensor Network (WSN) which, unlike the other methods/technologies, combines the desirable properties of low installation and maintenance cost, scalability and ability to perform measurements without interfering with the regular functioning of the airport. Due to the large extension of an airport and the difficulty of placing sensors over transit areas, the WSN might result segmented into a collection of subnetworks isolated from each other and from the sink. To overcome this problem, our proposal relies on a special type of node called Mobile Ubiquitous LAN Extension (MULE), able to move over the airport surface, gather data from the subnetworks along its way and eventually transfer it to the sink. One of the main demands for the deployment of any new system in an airport is that it must have little or no interference with the regular operations. This is why the use of an opportunistic approach for the transfer of data from the subnetworks to the MULE is favored in this thesis. By opportunistic we mean that the role of MULE will be played by some of the typical vehicles already existing in an airport doing their normal displacements, and the subnetworks will exploit any moment of contact with them to forward data to the sink. A particular characteristic of the MULEs in our application is that they move along predefined structured trajectories (given by the layout of the airport), having eventual contact with the set of nodes located by the side of the road (so-called subsinks). This implies the need for a data routing strategy to be used within each subnetwork, able to lead the collected data from the sensor nodes to the subsinks and distribute the data packets among them so that the time in contact with the MULE is used as efficiently as possible. In this thesis, we propose a routing protocol which undertakes this task. Our proposed protocol is named ACME, standing for ACO-based routing protocol for MULE-assisted WSNs. It is founded on the well known Ant Colony Optimization (ACO) technique. The main advantage of ACO is its natural fit to the decentralized nature of WSN, which allows it to perform distributed optimizations (based on local interactions) leading to remarkable overall network performance. ACME is able to assign sensor nodes to subsinks and generate the corresponding multi-hop paths while accounting for the minimization of the total path length, the total subsink imbalance and the total number of retransmissions. The problem is defined as a multi-objective optimization task which is resolved in a distributed manner based on actions of the sensor nodes acting in a collaborative scheme. We conduct a set of computational experiments in the discrete event simulator OMNeT++ which shows the advantages of our protocol in terms of performance and its ability to adapt to a variety of network topologie

Exploiting and optimizing mobility in wireless sensor networks

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia de Automação e Sistemas, Florianópolis, 2016.Nos últimos anos, as chamadas Redes de Sensores Sem Fio (RSSF) tem sido usadas numa grande variedade de aplicações, tais como monitoramento (p.ex. poluição do ar e água, vulcões, estruturas, sinais vitais), detecção de eventos (p.ex. vigilância, incêndios, inundações, terremotos), e monitoramento de alvos (p.ex. segurança, animais silvestres, etc). RSSF são constituídas tipicamente por dezenas, as vez centenas de pequenos dispositivos alimentados por baterias, capazes de realizar medições e de transmitir tais dados para uma estação base através de um canal sem fio. Uma das formas mais promissoras para melhorar o desempenho das RSSF em termos de conectividade, tempo de vida da rede, e latência na transmissão dos dados é através de técnicas que exploram a mobilidade em um ou mais componentes da rede. A mobilidade na RSSF pode ser tanto controlável como aleatória, sendo que em ambos os casos os protocolos devem ser devidamente ajustados para responder adequadamente aos cenários em questão. No caso de mobilidade aleatória, os nodos sensores podem ser capazes de aprender os padrões de mobilidade dos nodos para poderem otimizar a operação da rede. Por outro lado, sendo os padrões de mobilidade conhecidos, é possível fazer escolhas para melhor sintonizar o desempenho da rede de acordo com os critérios estabelecidos pelo projetista. A presente tese de doutorado procura explorar as vantagens associadas com o uso de mobilidade controlada em RSSF. É possível definir mobilidade controlada como sendo a capacidade de se alterar propositalmente o posicionamento de determinados nodos da RSSF. Com isso se torna possível explorar, controlar, ou mesmo otimizar a trajetória e a velocidade dos nodos móveis da RSSF a fim de maximizar o desempenho da rede como um todo. Definitivamente, o uso de nodos que permitam o ajuste de trajetória e velocidade oferece um alto grau de flexibilidade para se explorar aspectos de mobilidade e projetar protocolos de coleta de dados otimizados. Ao se utilizar mobilidade controlada, algumas das operações realizadas pela RSSF podem ser significativamente melhoradas, de modo a tornar possível ajustar o padrão de desempenho da rede de acordo com os níveis desejados. Por exemplo, o processo de descoberta de nodos pode ser melhorado e mesmo simplificado com o controle dos nodos móveis, de modo que ele possa se aproximar dos nodos estáticos em instantes pré-determinados. Da mesma forma, o processo de coleta de dados pode ser otimizado se os nodos móveis se moverem mais rapidamente nos locais onde eles precisam coletar menos dados. Entretanto, diversos desafios aparecem neste tipo de contexto. Por exemplo, como se deve escalonar a chegada do(s) nodo(s) móvel(is) e como se deve controlar e otimizar a movimentação em termos de velocidade sem afetar a qualidade de serviço. Nesse contexto, o segundo capítulo da teseapresenta um esquema de estimação de localização de nodos estáticos espalhados ao longo de uma área predeterminada, utilizando-se para tanto de um nodo móvel com mobilidade controlada. Tal informação de posicionamento é muito importante para a organização de uma RSSF. Com isso é possível definir a sua cobertura, os protocolos de roteamento, a forma de coleta de dados e também auxiliar em aplicações de rastreamento e detecção de eventos. O esquema proposto consiste de uma técnica de localização para estimar a posição dos nodos sensor de forma eficiente, usando apenas um nodo móvel e técnicas geométricas simples. O esquema não requer hardware adicional ou mesmo comunicação entre nodos sensores, evitando assim maiores gastos de baterias. A estimativa de posição obtida é precisa e capaz de tolerar um certo grau de obstáculos. Os resultados obtidos ao longo da tese demostram que a precisão de localização pode ser bem ajustada selecionando corretamente a velocidade, o intervalo de transmissão de beacons e o padrão de varredura da área de interesse pelo nodo móvel.Já o terceiro capítulo apresentada uma técnica de otimização para fins de controle da mobilidade do nodo coletor de dados (MDC). Com isso torna-se possível desenvolver um esquema inteligente de coleta de dados na RSSF. Em primeiro lugar, são destacados os fatores que afetam o processo de coleta de dados usando um MDC. Em seguida é apresentado um algoritmo adaptativo que permite ajustar os parâmetros de controlenecessários para modificar os parâmetros de movimentação do MDC. Estes parâmetros permitem que a velocidade do MDC seja ajustada em tempo de execução para otimizaro processo de coleta de dados. Com isso o MDC pode se adaptar às diferentes taxas de coletas de dados impostas por um conjunto de nodos heterogêneos. O esquema proposto apresenta vantagens significativas para RSSF de grande escala e também heterogêneas (onde os sensores possuem taxas de amostragem variáveis). Os resultados obtidos mostram um aumento significativo na taxa de coleta de dados e a redução no tempo total de deslocamento e no número de voltas que o MDC gasta para coletar os dados dos sensores.Por fim, o capítulo 4 propõe um mecanismo de controle de acesso (MAC) adaptado ao cenário de mobilidade, que se ajusta automaticamente de acordo com o padrão de mobilidade do MDC. O mesmo foca umaredução no consumo de energia e na melhoria da coleta de dados, suportando mobilidade e evitando colisões de mensagens. Este protocolo destina-se a aplicações de coleta de dados nas quais os nós sensores têm de reportar periodicamente a um nó receptor ou estação base. O conceito básico é baseado em acesso múltiplo de divisão de tempo, onde a duração do padrão de sono-vigília é definida de acordo com o padrão de mobilidade do MDC. O esquema proposto é capaz de atender tanto mobilidade aleatória quanto controlada por parte do MDC, desde que as RSSF sejam organizadas em cluster. Uma análise de simulação detalhada é realizada para avaliar seu desempenho em cenários mais gerais e sob diferentes condições operacionais. Os resultados obtidos mostram que o nosso esquema proposto supera amplamente oprotocolo 802.15.4 com sinais (beacons) em termos de eficiência energética, tempo de deslocamento do MDC e taxas de coleta de dados.Abstract : One of the promising techniques for improving the performance of a wireless sensor network (WSN), in terms of connectivity, network lifetime, and data latency, is to introduce and exploit mobility in some of the network components. Mobility in WSN can be either uncontrollable or controllable and needs to be optimized in both cases. In the case of uncontrolled mobility, sensor nodes can learn the mobility patterns of mobile nodes to improve network performance. On the other hand, if the mobility is controllable in terms of trajectory and speed, it can be best tuned to enhance the performance of the network to the desired level. This thesis considers the problem of exploiting and optimizing mobility in wireless sensor networks in order to increase the performance and efficiency of the network.First, a location estimation scheme is discussed for static nodes within a given sensor area using a controlled mobile node. Position information of static nodes is very important in WSN. It helps in effective coverage, routing, data collection, target tracking, and event detection. The scheme discusses a localization technique for efficient position estimation of the sensor nodes using a mobile node and simple geometric techniques. The scheme does not require extra hardware or data communication and does not make the ordinary sensor nodes to spend energy on any interaction with neighboring nodes. The position estimation is accurate and efficient enough to tolerate obstacles and only requires broadcasting of beacon messages by the mobile node. Obtained simulation results show that the localization accuracy can be well adjusted by properly selecting the speed, beacon interval, and scan pattern of the mobile node.Second, an optimization technique for controlled mobility of a mobile data collector is presented in order to develop a smart data collection scheme in WSN. In this case, first, the factors affecting the data collection process using an MDC is highlighted. Then, an adaptive algorithm and control parameters that the MDC uses for autonomously controlling its motion is presented. These parameters allow the speed of the MDC to be adjusted at run time in order to adaptively improve the data collection process. Built-in intelligence helps our system adapting to the changing requirements of data collection. Our scheme shows significant advantages for sparsely deployed, large scale sensor networks and heterogeneous networks (where sensors have variable sampling rates). The simulation results show a significant increase in data collection rate and reduction in the overall traverse time and number of laps that the MDC spends for data gathering.Finally, a mobility aware adaptive medium access control (MAC) is proposed for WSNs which automatically adjusts according to the mobility pattern of the MDC, focusing on reducing energy consumption and improving data collection, while supporting mobility and collision avoidance. This protocol is targeted to data collection applications (e.g. monitoring and surveillance), in which sensor nodes have to periodically report to a sink node. The core concept is based on adaptive time division multiple access, where the sleep-wake duration is defined according to the MDC mobility pattern. The proposed scheme is described for random, predictable, and controlled arrival of MDC in cluster-based WSNs. A detailed simulation analysis is carried out to evaluate its performance in more general scenarios and under different operating conditions. The obtained results show that our scheme largely outperforms the commonly used 802.15.4 beacon-enabled and other fixed duty-cycling schemes in terms of energy efficiency, MDC traverse time, and data collection rates

COLOMBO Deliverable 1.1: Scenario Specifications and Required Modifications to Simulation Tools

While targeting on supporting descriptions of scenarios and extensions to the simulation suite, the document additionally delivers a complete overview of the evaluation procedures to use in COLOMBO. Starting with an overview of the evaluation process, based on work done in the FESTA project, the document includes definitions of the performance indicators to use. These were originally produced by the iTETRIS project (by consortium partners of COLOMBO, mainly) and was extended within COLOMBO by performance indicators that describe the behaviour of inter-vehicle communication. To put the work on a scientific ground, a performed comparison of 40 scientific simulation studies is given, that shows that no standard scenarios and metrics exist. Additionally the document lists feature extensions which shall be implemented into the simulation tools within the COLOMBO project. Applicable software and data yielding to the scenarios were provided to the COLOMBO partners. As targeted, the document lists the scenarios made available within COLOMBO, distinguishing synthetic and real-world scenarios. Overall, seven scenarios based on real-world data were made available. Additionally, a tool that allows generating a large variety of synthetic scenarios is presented. The document ends with an extension (against the one given in D5.1) of requirements put on the simulations suite

Design, analysis and implementation of a spatial-temporal, adaptive and multi-replication data centric storage framework for wireless sensor and actor networks

This PhD Thesis presents a novel framework for Data-Centric Storage(DCS) in a Wireless Sensor and Actor Network(WSAN) that enables the use of a multiple set of data replication nodes, which also change over the time. This allows reducing the average network traffic and energy consumption by adapting the number of replicas to applications’ traffic, while balancing energy burdens by varying their location. To that end we propose and validate a simple model to determine the optimal number of replicas, in terms of minimizing average traffic/energy consumption, from the measured applications’ production and consumption traffic. Simple mechanisms are proposed to decide when the current set of replication nodes should be changed, to enable new applications and sensor nodes to efficiently bootstrap into a working sensor network, to recover from failing nodes, and to adapt to changing conditions. Extensive simulations demonstrate that our approach can extend a sensor network’s lifetime by at least a 60%, and up to a factor of 10x depending on the lifetime criterion being considered. Furthermore, we have implemented our framework in a real testbed with 20 motes that validates in a small scenario those results obtained via simulation for large WSANs. Finally, we present a heuristic that adapts our framework to scenarios with spatially heterogeneous consumption and/or production traffic distributions providing an effective reduction in the overall traffic, as well as reducing the number of nodes that die over the time. --------------------------------------------------------------------------------------------------------------------------------------------Esta Tesis se enmarca en el campo de la redes de sensores y actuadores inalámbricas. Para este tipo de redes existe un sistema de almacenamiento y entrega de información totalmente distribuido denominado Data-Centric Storage (DCS). En dicho sistema se selecciona un nodo en la red para almacenar toda la información relativa a una aplicación o tipo de evento. Dicha elección se realiza mediante el uso de una función de hash que, usando como argumento el propio nombre de la aplicación (o tipo de evento), devuelve el identificador (e.g. coordenadas geográficas, identificador de nodo, etc) del nodo responsable de almacenar toda la información que deesa aplicación (o tipo de evento). El uso de un único nodo para almacenar todos los datos de un mismo tipo generados en la red tiende a generar un punto de saturación en la red (especialmente en términos energéticos) ya que una gran cantidad de tráfico es encaminada hacia un único punto. De hecho, no sólo el nodo seleccionado como nodo de almacenamiento, sino también todos aquellos que le rodean, experimentan un mayor gasto de recursos ya que son los encargados de rutar los mensajes hacia el nodo de almacenamiento. Este problema ha dado lugar a sistemas que utilizan multiples réplicas para aliviar la generacióon de un punto de congestión y elevado consumo energético en la red. Situando varios puntos de almacenamiento para un tipo de evento dado, es posible aliviar la congestión de un único punto. Sin embargo la generación de nuevas réplicas tiene un coste asociado, y por tanto existe un número de réplicas óptimo que minimiza el tráfico total en la red, que a su vez tiene un impacto directo en la reducción del consumo energético y la extensión del tiempo de vida de la red. En esta Tesis se proponen dos esquemas de replicación para redes de sensores que usan DCS como sistema de almacenamiento distribuido. Para ambos casos se han desarrollado modelos matemáticos que permiten conocer el número óptimo de réplicas que deben ser utilizadas (para minimizar el tráfico total en la red) en función de la intensidad de producción y consumo de un tipo de evento. El primer mecanismo, denominado Quadratic Adaptive Replication (QAR), propone el uso de una estructura mallada para la colocación de las réplicas. QAR mejora trabajos previos que ya proponían un esquema de replicación en grid, ya que es más adaptativo a las condiciones de tráfico en la red. El segundo mecanismo simplemente genera localizaciones aleatorias donde situar las replicas. Sorprendentemente, esta Tesis demuestra que es el mejor sistema de replicación, incluso por delante de QAR, ya que es el más adaptativo a las condiciones de tráfico. Además, tiene la gran ventaja de que es extremadamente simple y puede aplicarse en redes irregulares o que utlizan diferentes protocolos de enrutamiento. Los sistemas de replicación alivian el problema del punto único de congestión, pero no lo solucionan completamente, ya que siguen apareciendo puntos de congestión menores, tantos como réplicas sean usadas. Por tanto, la red sigue presentando una gran desigualdad en el consumo energético, ya que aquellos puntos seleccionados como réplicas (y sus vecinos) usan una mayor energía para desarrollar su actividad. Frente a este problema, se propone como solución el cambio de las réplicas a lo largo del tiempo. Esecialmente, se limita el tiempo que un nodo puede permanecer desempeñando el papel de réplica, de tal forma que, una vez pasado ese tiempo, otro nodo tomará esa responsabilidad. Aplicando esta propuesta se consigue un equilibrio en el consumo energético de los nodos de la red, lo que tiene un gran impacto en la extensión del tiempo de vida de la red. En los experimentos realizados, dicha extensión tiene un valor m´ınimo de un 60%, llegándose a extender el tiempo de la vida hasta 10 veces bajo ciertas definiciones de tiempo de vida de la red. La principal contribución de esta Tesis es la presentación de un marco de trabajo adaptativo tanto espacial como temporalmente que, basado en un modelo teórico, indica cuál es el número óptimo de replicas que deben ser usadas en un determinado periodo. En esta Tesis se propone un protocolo completo que cubre todas las funcionalidades para que dicho sistema pueda ser implementado y desplegado en el mundo real. Para demostrar que el sistema propuesto puede ser implementado en ndoos de sensores comerciales, esta Tesis presenta la implementación realizada en 20 motas del fabricante Jennic. Asimismo, se ha empleado un pequeño test de pruebas para confirmar la validez de los modelos matemáticos para la obtención del número óptimo de réplicas, así como para demostrar que el cambio de las réplicas a lo largo del tiempo genera una mejor distribución del consumo energético en la red