Topology Design to Increase Network Lifetime in WSN for Graph Filtering in Consensus Processes

Graph filters, which are considered as the workhorses of graph signal analysis in the emerging field of signal processing on graphs, are useful for many applications such as distributed estimation in wireless sensor networks. Many of these tasks are based on basic distributed operators such as consensus, which are carried out by sensor devices under limited energy supply. To cope with the energy constraints, this paper focuses on designing the network topology in order to maximize the network lifetime and reduce the energy consumption when applying graph filters. The problem is a complex combinatorial problem and in this work, we propose two efficient heuristic algorithms for solving it. We show by simulations that they provide good performance in terms of the network lifetime and the total energy consumption of the filtering process.acceptedVersionnivå

Distributed Detection and Estimation in Wireless Sensor Networks

In this article we consider the problems of distributed detection and estimation in wireless sensor networks. In the first part, we provide a general framework aimed to show how an efficient design of a sensor network requires a joint organization of in-network processing and communication. Then, we recall the basic features of consensus algorithm, which is a basic tool to reach globally optimal decisions through a distributed approach. The main part of the paper starts addressing the distributed estimation problem. We show first an entirely decentralized approach, where observations and estimations are performed without the intervention of a fusion center. Then, we consider the case where the estimation is performed at a fusion center, showing how to allocate quantization bits and transmit powers in the links between the nodes and the fusion center, in order to accommodate the requirement on the maximum estimation variance, under a constraint on the global transmit power. We extend the approach to the detection problem. Also in this case, we consider the distributed approach, where every node can achieve a globally optimal decision, and the case where the decision is taken at a central node. In the latter case, we show how to allocate coding bits and transmit power in order to maximize the detection probability, under constraints on the false alarm rate and the global transmit power. Then, we generalize consensus algorithms illustrating a distributed procedure that converges to the projection of the observation vector onto a signal subspace. We then address the issue of energy consumption in sensor networks, thus showing how to optimize the network topology in order to minimize the energy necessary to achieve a global consensus. Finally, we address the problem of matching the topology of the network to the graph describing the statistical dependencies among the observed variables.Comment: 92 pages, 24 figures. To appear in E-Reference Signal Processing, R. Chellapa and S. Theodoridis, Eds., Elsevier, 201

Dynamic distributed clustering in wireless sensor networks via Voronoi tessellation control

This paper presents two dynamic and distributed clustering algorithms for Wireless Sensor Networks (WSNs). Clustering approaches are used in WSNs to improve the network lifetime and scalability by balancing the workload among the clusters. Each cluster is managed by a cluster head (CH) node. The first algorithm requires the CH nodes to be mobile: by dynamically varying the CH node positions, the algorithm is proved to converge to a specific partition of the mission area, the generalised Voronoi tessellation, in which the loads of the CH nodes are balanced. Conversely, if the CH nodes are fixed, a weighted Voronoi clustering approach is proposed with the same load-balancing objective: a reinforcement learning approach is used to dynamically vary the mission space partition by controlling the weights of the Voronoi regions. Numerical simulations are provided to validate the approaches

Intelligent Sensor Networks

In the last decade, wireless or wired sensor networks have attracted much attention. However, most designs target general sensor network issues including protocol stack (routing, MAC, etc.) and security issues. This book focuses on the close integration of sensing, networking, and smart signal processing via machine learning. Based on their world-class research, the authors present the fundamentals of intelligent sensor networks. They cover sensing and sampling, distributed signal processing, and intelligent signal learning. In addition, they present cutting-edge research results from leading experts

Intrusion tolerant routing with data consensus in wireless sensor networks

Dissertação para obtenção do Grau de Mestre em Engenharia InformáticaWireless sensor networks (WSNs) are rapidly emerging and growing as an important new area in computing and wireless networking research. Applications of WSNs are numerous, growing, and ranging from small-scale indoor deployment scenarios in homes and buildings to large scale outdoor deployment settings in natural, industrial, military and embedded environments. In a WSN, the sensor nodes collect data to monitor physical conditions or to measure and pre-process physical phenomena, and forward that data to special computing nodes called Syncnodes or Base Stations (BSs). These nodes are eventually interconnected, as gateways, to other processing systems running applications. In large-scale settings, WSNs operate with a large number of sensors – from hundreds to thousands of sensor nodes – organised as ad-hoc multi-hop or mesh networks, working without human supervision. Sensor nodes are very limited in computation, storage, communication and energy resources. These limitations impose particular challenges in designing large scale reliable and secure WSN services and applications. However, as sensors are very limited in their resources they tend to be very cheap. Resilient solutions based on a large number of nodes with replicated capabilities, are possible approaches to address dependability concerns, namely reliability and security requirements and fault or intrusion tolerant network services. This thesis proposes, implements and tests an intrusion tolerant routing service for large-scale dependable WSNs. The service is based on a tree-structured multi-path routing algorithm, establishing multi-hop and multiple disjoint routes between sensors and a group of BSs. The BS nodes work as an overlay, processing intrusion tolerant data consensus over the routed data. In the proposed solution the multiple routes are discovered, selected and established by a self-organisation process. The solution allows the WSN nodes to collect and route data through multiple disjoint routes to the different BSs, with a preventive intrusion tolerance approach, while handling possible Byzantine attacks and failures in sensors and BS with a pro-active recovery strategy supported by intrusion and fault tolerant data-consensus algorithms, performed by the group of Base Stations

A critical analysis of research potential, challenges and future directives in industrial wireless sensor networks

In recent years, Industrial Wireless Sensor Networks (IWSNs) have emerged as an important research theme with applications spanning a wide range of industries including automation, monitoring, process control, feedback systems and automotive. Wide scope of IWSNs applications ranging from small production units, large oil and gas industries to nuclear fission control, enables a fast-paced research in this field. Though IWSNs offer advantages of low cost, flexibility, scalability, self-healing, easy deployment and reformation, yet they pose certain limitations on available potential and introduce challenges on multiple fronts due to their susceptibility to highly complex and uncertain industrial environments. In this paper a detailed discussion on design objectives, challenges and solutions, for IWSNs, are presented. A careful evaluation of industrial systems, deadlines and possible hazards in industrial atmosphere are discussed. The paper also presents a thorough review of the existing standards and industrial protocols and gives a critical evaluation of potential of these standards and protocols along with a detailed discussion on available hardware platforms, specific industrial energy harvesting techniques and their capabilities. The paper lists main service providers for IWSNs solutions and gives insight of future trends and research gaps in the field of IWSNs

Routing and Mobility on IPv6 over LoWPAN

The IoT means a world-wide network of interconnected objects based on standard communication protocols. An object in this context is a quotidian physical device augmented with sensing/actuating, processing, storing and communication capabilities. These objects must be able to interact with the surrounding environment where they are placed and to cooperate with neighbouring objects in order to accomplish a common objective. The IoT objects have also the capabilities of converting the sensed data into automated instructions and communicating them to other objects through the communication networks, avoiding the human intervention in several tasks. Most of IoT deployments are based on small devices with restricted computational resources and energy constraints. For this reason, initially the scientific community did not consider the use of IP protocol suite in this scenarios because there was the perception that it was too heavy to the available resources on such devices. Meanwhile, the scientific community and the industry started to rethink about the use of IP protocol suite in all IoT devices and now it is considered as the solution to provide connectivity between the IoT devices, independently of the Layer 2 protocol in use, and to connect them to the Internet. Despite the use of IP suite protocol in all devices and the amount of solutions proposed, many open issues remain unsolved in order to reach a seamless integration between the IoT and the Internet and to provide the conditions to IoT service widespread. This thesis addressed the challenges associated with the interconnectivity between the Internet and the IoT devices and with the security aspects of the IoT. In the interconnectivity between the IoT devices and the Internet the problem is how to provide valuable information to the Internet connected devices, independently of the supported IP protocol version, without being necessary accessed directly to the IoT nodes. In order to solve this problem, solutions based on Representational state transfer (REST) web services and IPv4 to IPv6 dual stack transition mechanism were proposed and evaluated. The REST web service and the transition mechanism runs only at the border router without penalizing the IoT constrained devices. The mitigation of the effects of internal and external security attacks minimizing the overhead imposed on the IoT devices is the security challenge addressed in this thesis. Three different solutions were proposed. The first is a mechanism to prevent remotely initiated transport level Denial of Service attacks that avoids the use of inefficient and hard to manage traditional firewalls. It is based on filtering at the border router the traffic received from the Internet and destined to the IoT network according to the conditions announced by each IoT device. The second is a network access security framework that can be used to control the nodes that have access to the network, based on administrative approval, and to enforce security compliance to the authorized nodes. The third is a network admission control framework that prevents IoT unauthorized nodes to communicate with IoT authorized nodes or with the Internet, which drastically reduces the number of possible security attacks. The network admission control was also exploited as a management mechanism as it can be used to manage the network size in terms of number of nodes, making the network more manageable, increasing its reliability and extending its lifetime.A IoT (Internet of Things) tem suscitado o interesse tanto da comunidade académica como da indústria, uma vez que os campos de aplicação são inúmeros assim como os potenciais ganhos que podem ser obtidos através do uso deste tipo de tecnologia. A IoT significa uma rede global de objetos ligados entre si através de uma rede de comunicações baseada em protocolos standard. Neste contexto, um objeto é um objeto físico do dia a dia ao qual foi adicionada a capacidade de medir e de atuar sobre variáveis físicas, de processar e armazenar dados e de comunicar. Estes objetos têm a capacidade de interagir com o meio ambiente envolvente e de cooperar com outros objetos vizinhos de forma a atingirem um objetivo comum. Estes objetos também têm a capacidade de converter os dados lidos em instruções e de as comunicar a outros objetos através da rede de comunicações, evitando desta forma a intervenção humana em diversas tarefas. A maior parte das concretizações de sistemas IoT são baseados em pequenos dispositivos autónomos com restrições ao nível dos recursos computacionais e de retenção de energia. Por esta razão, inicialmente a comunidade científica não considerou adequado o uso da pilha protocolar IP neste tipo de dispositivos, uma vez que havia a perceção de que era muito pesada para os recursos computacionais disponíveis. Entretanto, a comunidade científica e a indústria retomaram a discussão acerca dos benefícios do uso da pilha protocolar em todos os dispositivos da IoT e atualmente é considerada a solução para estabelecer a conetividade entre os dispositivos IoT independentemente do protocolo da camada dois em uso e para os ligar à Internet. Apesar do uso da pilha protocolar IP em todos os dispositivos e da quantidade de soluções propostas, são vários os problemas por resolver no que concerne à integração contínua e sem interrupções da IoT na Internet e de criar as condições para a adoção generalizada deste tipo de tecnologias. Esta tese versa sobre os desafios associados à integração da IoT na Internet e dos aspetos de segurança da IoT. Relativamente à integração da IoT na Internet o problema é como fornecer informação válida aos dispositivos ligados à Internet, independentemente da versão do protocolo IP em uso, evitando o acesso direto aos dispositivos IoT. Para a resolução deste problema foram propostas e avaliadas soluções baseadas em web services REST e em mecanismos de transição IPv4 para IPv6 do tipo pilha dupla (dual stack). O web service e o mecanismo de transição são suportados apenas no router de fronteira, sem penalizar os dispositivos IoT. No que concerne à segurança, o problema é mitigar os efeitos dos ataques de segurança internos e externos iniciados local e remotamente. Foram propostas três soluções diferentes, a primeira é um mecanismo que minimiza os efeitos dos ataques de negação de serviço com origem na Internet e que evita o uso de mecanismos de firewalls ineficientes e de gestão complexa. Este mecanismo filtra no router de fronteira o tráfego com origem na Internet é destinado à IoT de acordo com as condições anunciadas por cada um dos dispositivos IoT da rede. A segunda solução, é uma framework de network admission control que controla quais os dispositivos que podem aceder à rede com base na autorização administrativa e que aplica políticas de conformidade relativas à segurança aos dispositivos autorizados. A terceira é um mecanismo de network admission control para redes 6LoWPAN que evita que dispositivos não autorizados comuniquem com outros dispositivos legítimos e com a Internet o que reduz drasticamente o número de ataques à segurança. Este mecanismo também foi explorado como um mecanismo de gestão uma vez que pode ser utilizado a dimensão da rede quanto ao número de dispositivos, tornando-a mais fácil de gerir e aumentando a sua fiabilidade e o seu tempo de vida