The research in distributed algorithms is linked with the developments of statistical inference in wireless sensor networks (WSNs) applications. Typically, distributed approaches process the collected signals from networked sensor nodes. That is to say, the sensors receive local observations and transmit information between each other. Each sensor is capable of combining the collected information with its own observations to improve performance. In this thesis, we propose novel distributed methods for the inference applications using wireless sensor networks. In particular, the efficient algorithms which are not computationally intensive are investigated. Moreover, we present a number of novel algorithms for processing asynchronous network events and robust state estimation. In the first part of the thesis, a distributed adaptive algorithm based on the component-wise EM method for decentralized sensor networks is investigated. The distributed component-wise Expectation-Maximization (EM) algorithm has been designed for application in a Gaussian density estimation. The proposed algorithm operates a component-wise EM procedure for local parameter estimation and exploit an incremental strategy for network updating, which can provide an improved convergence rate. Numerical simulation results have illustrated the advantages of the proposed distributed component-wise EM algorithm for both well-separated and overlapped mixture densities. The distributed component-wise EM algorithm can outperform other EM-based distributed algorithms in estimating overlapping Gaussian mixtures. In the second part of the thesis, a diffusion based EM gradient algorithm for density estimation in asynchronous wireless sensor networks has been proposed. Specifically, based on the asynchronous adapt-then-combine diffusion strategy, a distributed EM gradient algorithm that can deal with asynchronous network events has been considered. The Bernoulli model has been exploited to approximate the asynchronous behaviour of the network. Compared with existing distributed EM based estimation methods using a consensus strategy, the proposed algorithm can provide more accurate estimates in the presence of asynchronous networks uncertainties, such as random link failures, random data arrival times, and turning on or off sensor nodes for energy conservation. Simulation experiments have been demonstrated that the proposed algorithm significantly outperforms the consensus based strategies in terms of Mean-Square- Deviation (MSD) performance in an asynchronous network setting. Finally, the challenge of distributed state estimation in power systems which requires low complexity and high stability in the presence of bad data for a large scale network is addressed. A gossip based quasi-Newton algorithm has been proposed for solving the power system state estimation problem. In particular, we have applied the quasi-Newton method for distributed state estimation under the gossip protocol. The proposed algorithm exploits the Broyden- Fletcher-Goldfarb-Shanno (BFGS) formula to approximate the Hessian matrix, thus avoiding the computation of inverse Hessian matrices for each control area. The simulation results for IEEE 14 bus system and a large scale 4200 bus system have shown that the distributed quasi-Newton scheme outperforms existing algorithms in terms of Mean-Square-Error (MSE) performance with bad data.

Made available in DSpace on 2015-04-22T22:00:54Z (GMT). No. of bitstreams: 1 Dissertacao_Alyson.pdf: 2045006 bytes, checksum: 552fa4e2c7d4a7aa118296a3b4324aa2 (MD5) Previous issue date: 2011-09-09 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Wireless Sensor Networks (WSNs) revolutionize the monitoring of environment, enabling the creation of applications and scenarios in various areas of knowledge. As a consequence, we have a very fast growth of the development of new applications and rata increase of system complexity and cost of proposed development. The difficulty in developing new applications is not only due to restrictive features (memory, processor, power), but also by the instructions of low-level programming these networks. This situation is conductive to the creation of new methodologies and tools that support the development of system for that plataform. This work proposes the development of a tool called automatic code generation for wireless sensor network (WSN-GAC), which has as its main objective to enable any product high in developing applications for WSNs using models specified in Model driven architecture (MDA). WSN-GAC receives as input a model of a component-based application created by the designer and then performs automatic code generation of nesC (network embedded system C). Three case studied demonstrate the potential of WSN-GAC to help developers of applications for these networks. / As Redes de Sensores Sem Fio (RSSFs) revolucionam a monitoração de ambientes, possibilitando a criação de aplicações e cenários nas mais diversas áreas do conhecimento. Como consequência, temos o crescimento muito rápido do desenvolvimento de novas aplicações e proporcionalmente aumento de complexidade dos sistemas propostos e do custo de desenvolvimento. A dificuldade no desenvolvimento de novas aplicações não se deve somente às características restritivas (memória, processamento, energia), mas também pelas instruções de programação de baixo nível destas redes. Este panorama é favorável a criação de novas metodologias e ferramentas que dêem suporte ao desenvolvimento de sistemas para tal plataforma. Este trabalho propõe o desenvolvimento de uma ferramenta intitulada Geração Automática de Código para Redes de Sensores Sem Fio (GAC-RSSFs), que tem como objetivo principal possibilitar a alta produtividade no desenvolvimento de aplicações para as RSSFs utilizando modelos especificados na Arquitetura Orientada a Modelos (Model Driven Architecture - MDA). GAC-RSSFs recebe como entrada um modelo baseado em componentes de uma aplicação criada pelo projetista e então realiza a geração automática de código em linguagem nesC (network embedded systems C). Três estudos de caso demonstram o potencial de GAC-RSSFs para ajudar os desenvolvedores de aplicações para essas redes.

<p>Wireless mesh networks are widely used for various communication purposes and are often deployed in a broad range of outdoor applications. In cases where the deployment area is outside the reach of fixed infrastructure, energy efficient operation of the mesh nodes is very important. Many approaches have been explored to find energy efficient network solutions for these types of scenarios. This thesisproposes power saving mechanisms where the mesh network nodes opportunistically access coexistent vehicular networks. This is referred to as Opportunistic Vehicle Assisted Ferrying (OVAF). The history of using moving particles for message carrying can be found in research on intermittently connected networks. However, this approachhas never been considered with fully connected networks. Two different models are presented to model the OVAFmechanism: \textbf{a}. \emph{A flow based model}, and \textbf{b}. \emph{Apacket based model}. For each model an analytic lower bound isobtained by formulating a linear integer optimization with differentcost functions. Heuristics, which simplify the complexity of theproblem, are then developed for eachmodel. Arriving vehicles and generated packets are also modeled asrandom processes under various scenarios using different parameters.Results are presented which demonstrate the superiority of the OVAFrouting method compared to conventional multihop forwarding (Up to $60\%$increase in energy saving).</p> / Master of Applied Science (MASc)

Yes / The recent advancements in wireless sensor hardware ensures sensing multiple sensor data such as temperature, pressure, humidity, etc. using a single hardware unit, thus defining it as multi-sensor data communication in wireless sensor networks (WSNs). The in-processing technique of data aggregation is crucial in energy-efficient WSNs; however, with the requirement of end-to-end data confidentiality it may prove to be a challenge. End-to-end data confidentiality along with data aggregation is possible with the implementation of a special type of encryption scheme called privacy homomorphic (PH) encryption schemes. This paper proposes an optimized PH encryption scheme for WSN integrated networks handling multi-sensor data. The proposed scheme ensures light-weight payloads, significant energy and bandwidth consumption along with lower latencies. The performance analysis of the proposed scheme is presented in this paper with respect to the existing scheme. The working principle of the multi-sensor data framework is also presented in this paper along with the appropriate packet structures and process. It can be concluded that the scheme proves to decrease the payload size by 56.86% and spend an average energy of 8-18 mJ at the aggregator node for sensor nodes varying from 10-50 thereby ensuring scalability of the WSN unlike the existing scheme.

Les Réseaux de Capteurs Sans Fils (RCSFs) et les réseaux véhiculaires sont de plus en plus répandus, et déployés dans des domaines d’applications variés tels que la santé, la surveillance environnementale, les applications d’alerte d’accident, et les applications militaires. Cependant, ces réseaux peuvent être sujets à des attaques, ce qui empêche leur utilisation à grande échelle. Cette thèse étudie la sécurité des communications pour les réseaux de capteurs sans fils, et les communications inter-véhiculaires. Dans ce but, nous abordons quatre aspects importants. La première étude porte sur l’authentification des messages diffusés dans les réseaux de capteurs. Nous nous concentrons sur les principaux schémas à base de divulgation de clés d’authentification. Nous démontrons que le délai de divulgation de clé induit un délai d’authentification, ce qui pourrait conduire à une attaque de mémoire de déni de service. Nous proposons ensuite deux protocoles d’authentification de la source dans les RCSFs, pour surmonter la vulnérabilité des solutions existantes. Les schémas proposés garantissent la gestion efficace de la mémoire tampon du récepteur, en utilisant un mécanisme d’authentification par niveau, et une structure de Filtre de Bloom afin de réduire le coût de communication. Ensuite, nous validons nos protocoles en utilisant l’outil de vérification AVISPA, et nous les évaluons avec des expérimentations dans l’environment TinyOS. Nous confirmons que ces protocoles fournissent un service d’authentification de la source tout en respectant les contraintes de RCSFs. La seconde étude porte sur le problème de stockage au niveau des capteurs. Nous considérons en particulier l’attaque d’authentification différée “Delayed Authentication Compromise” (DAC) dans les RCSFs, qui permet à un attaquant d’utiliser une clé déjà divulguée pour signer d’autres messages. Nous montrons d’abord que les systèmes récemment proposés qui sont résistants également à l’attaque DAC sont vulnérables aussi à deux types d’attaques: attaque de permutation de commandes (où un adversaire prétend “permuter” deux messages au fil du temps), et l’attaque de rejet de commandes (où un adversaire semble “cacher” un message envoyé par la station de base). Nous proposons ensuite une nouvelle solution d’authentification. Notre analyse montre que notre solution est efficace pour détecter à la fois l’attaque de permutation de commandes et l’attaque de rejet de commandes, — et en même temps — est plus efficace (en termes de communication et de calcul) que les solutions existantes. xxiDans la troisième étude, nous considérons le problème de la sécurité de la gestion des clés dans les réseaux de capteurs. Nous présentons de nouveaux schémas d’authentification à base de clés symétriques qui présentent un faible coût d’authentification et de communication. Nos systèmes sont construits en intégrant un mécanisme de réputation, un filtre de Bloom, et un arbre binaire de clés pour la distribution et la mise à jour des clés d’authentification. Nos schémas d’authentification sont efficaces en matière de communication et de consommation de l’énergie. La quatrième étude porte sur la sécurité des communications véhiculaires. Nous nous concentrons sur les applications d’alerte d’accident. Nous analysons les menaces pour un ensemble d’algorithmes. Nous démontrons que ces systèmes sont vulnérables à l’attaque d’injection d’une fausse position, à l’attaque de rejeu de message d’alerte, et à l’attaque d’interruption de message d’alerte. Ensuite, nous proposons des contre-mesures à ces menaces. Nous avons donc proposé une solution qui est à la fois rapide et sécurisée pour les applications d’alerte d’accident : Un algorithme rapide et sécurisé pour la diffusion des messages en multi-saut (FS-MBA). Enfin, nous confirmons l’efficacité et la faisabilité des différents protocoles en effectuant un ensemble de simulations sous le simulateur NS-2. / Wireless sensor and vehicular networks play an important role in critical military and civil applications, and pervade our daily life. However, security concerns constitute a potential stumbling block to the impeding wide deployment of sensor networks and vehicular communications. This dissertation studies communication security for Wireless Sensor Networks (WSNs), and vehicular communication. To this aim, we address four important aspects. The first study addresses broadcast authentication in WSNs. We focus on key disclosure based schemes. We demonstrate that key disclosure delay induces an authentication delay, which could lead to a memory DoS attack. We then propose two broadcastauthentication protocols for WSNs, which overcome the security vulnerability of existingsolutions. The proposed schemes guarantee the efficient management of receiver’s buffer, by employing a staggered authentication mechanism, and a Bloom filter data structure to reduce the communication overhead. We also validate our protocols under the AVISPA model checking tool, and we evaluate them with experiments under TinyOS. Our findings are that these protocols provide source authentication service while respecting the WSN constraints.The second study addresses the storage issue in WSNs, in particular the Delayed AuthenticationCompromise attack (DAC). We first demonstrate that recently proposed schemes, which also address the DAC issue are vulnerable to two kinds of attacks: switch command attack (where an adversary pretends to “switch” two messages over time), and drop command attack (where an adversary just pretends to “hide” a message sent from the broadcaster). As a countermeasure against these attacks, we propose a new solution for broadcast authentication. Our analysis shows that our solution is effective in detecting both switch command and drop command attack, and—at the same time—is more efficient (in terms of both communication and computation) than the state of the art solutions.In the third study, we address key management security in WSNs. We present novel symmetric-key-based authentication schemes which exhibit low computation and communication authentication overhead. Our schemes are built upon the integration of a reputation mechanism, a Bloom filter, and a key binary tree for the distribution and updating of the auxviii thentication keys. Our schemes are lightweight and efficient with respect to communication and energy overhead. The fourth study addresses security in vehicular communications. We focus on fast multi hop broadcast applications. We analyze the security threats of state of the art vehicular based safety applications. We demonstrate that these schemes are vulnerable to the position cheating attack, the replay broadcast message attack, and the interrupting forwarding attack. Then, we propose countermeasures for these threats. We hence propose a complete solution which is both fast and secure in broadcasting safety related messages: Fast and Secure Multi-hop Broadcast Algorithm (FS-MBA). Finally, we confirm the efficiency and feasibility of our proposals using an extensive set of simulations under NS-2 Simulator.

For large multihop networks, the time synchronization (TS) error accumulates as the hop number increases with conventional methods, such as Timing-sync Protocol for Sensor Networks (TPSN), Reference Broadcast Synchronization (RBS), and Flooding Time Synchronization Protocol (FTSP). In this paper, to reduce the number of hops to cover the large network and exploit the spatial averaging of TS error between clusters, a novel method combining Concurrent Cooperative Transmission (CCT) and Semi-Cooperative Spectrum Fusion (SCSF) is proposed. This novel method named Cooperative Analog and Digital (CANDI) Time Synchronization protocol consists of two phases: The digital stage and the analog stage. The digital stage uses CCT to broadcast TS packet containing the time information. Cooperating nodes transmit the digitally encoded message in orthogonal channels simultaneously, so the receiver combines the multiple packet to acheive significant SNR advantage. In the analog stage, the cooperating nodes simultaneously transmit their slightly different individual estimates of the propagation time by using frequency shift modulation. Nodes receiving this signal combat fading and reduce estimation error in one step through the averaging inherent in diversity combining. Simulation results for two-dimension (2-D) networks are given to evaluate the performance of CANDI, and CANDI is compared with TPSN.

In the last few years, wireless sensor networks (WSNs) have become a very actively researched area. The impetus for this spurt of interest were developments in wireless technologies and low-cost VLSI, that made it possible to build inexpensive sensors and actuators. Each such device has limited computational power, memory and energy supply. Nevertheless, because of the low cost, such devices can be deployed in large numbers, and can thereafter form a sensor network. Usually, one or more base stations are also present which act as sink nodes. When sensors are deployed in hostile environments, security becomes an integral part for such type of networks. A first step in this direction is to provide secure communication between any two nodes and between a node and the base station. Since the public key cryptographic techniques are computationally expensive for resource constrained sensors, one need to rely on symmetric key cryptography for secure communication. The distribution and management of cryptographic keys poses a unique challenge in sensor networks. One requires efficient key distribution algorithms for such type of networks. In this thesis, we address the problem of secure path key establishment in wireless sensor networks. We first propose a pairwise key distribution algorithm for probabilistic schemes. Inspired by the recent proxy-based schemes, we introduce a friend-based scheme for establishing pairwise keys securely. We show that the chances of finding friends in a neighbourhood are considerably more than that of finding proxies, leading to lower communication overhead. Further, we prove that the friend-based scheme performs better than the proxy-based scheme both in terms of resilience against node capture as well as in energy consumption for pairwise key establishment. A recent study has shown that the advantages of the probabilistic approach over the deterministic approach, are not as much as people have believed. Thus, we focus our attention on deterministic schemes in which we first discuss why one cannot use the conventional security measure for determining the resilience of a key distribution scheme in case of schemes in which nodes share more than one key. Then, we propose a new and a more general security metric for measuring the resilience of a key distribution scheme in wireless sensor networks. Further, we present a polynomial-based scheme and a novel complete connectivity scheme for distributing keys to sensors and show an analytical comparison, in terms of security and connectivity, between the schemes. Motivated by the schemes, we derive general expressions for the new security measure and the connectivity. A number of conclusions are made using these general expressions. Then, we conclude our work with a number of future directions that can be followed with this piece of work.

Τα ασύρματα δίκτυα αισθητήρων (WSNs) είναι πολύ αναγνωρισμένα στις μέρες μας και γύρω από αυτά έχουν αναπτυχθεί χιλιάδες εφαρμογές που με χρήση άλλης τεχνολογίας ήταν σχεδόν ακατόρθωτες. Ένα WSN αποτελείται από κόμβους οι οποίοι είναι προγραμματισμένοι να επικοινωνούν και να συλλέγουν πληροφορίες μέσω των αισθητήρων που είναι αναρτημένοι πάνω τους. Οι πληροφορίες ή σύνολο των πληροφοριών καταλήγουν τελικά στους κόμβους που είναι προγραμματισμένοι ως τερματικοί κόμβοι ή βάσεις. Οι βάσεις είναι συνήθως συνδεδεμένες με ένα υπολογιστή και μεταφέρουν τα δεδομένα του δικτύου σε αυτόν. Τα κύρια χαρακτηριστικά των ασύρματων δικτύων αισθητήρων είναι η χαμηλή κατανάλωση ενεργείας των συσκευών-κόμβων (motes), η σταθερότητα και η απλότητα του κώδικα καθώς και η μεγάλη αξιοπιστία. Μερικές εφαρμογές των WSNs είναι για παράδειγμα η μέτρηση της υγρασίας στον τάπητα ενός γηπέδου γκολφ, η παρακολούθηση των κρίσιμων μεγεθών σε μεγάλες κατασκευές (π.χ. οι τάσεις των νημάτων μιας κρεμμαστης γέφυρας ή η παρακολούθηση της καταπόνησης των δοκών ενός ουρανοξύστη). Στα πλαίσια της διπλωματικής εργασίας αυτής παρουσιάζουμε ένα ασύρματο δίκτυο αισθητήρων όπου οι αισθητήρες είναι έξυπνες κάμερες! Παρουσιάζει μεγάλο ενδιαφέρον η μελέτη ενός τέτοιου δικτύου καθώς και η ανάπτυξη εφαρμογών γύρω από αυτό. / Wireless Sensor Networks (WSNs) are very much recognized these days, and thousands of applications have been developed in relation to them, which, would have been impossible if other technologies were used. A WSN is made up of nodes programmed to collect information through sensors attached to them and transmit them. The information ends up finally to the nodes which are programmed as terminal nodes or base-stations. These base-stations are usually connected to a computer and transfer the data that have been retrieved from the network to it. The main features of a WSN is the low energy consumption by the node equipment (motes), the stability and simplicity of the code as well as their great reliability. Some applications of the WSNs are, for example, the measurement of humidity in a golf course, the monitoring of the crucial sizes in great constructions (e.g. the tensions of the fibers in a suspension bridge, the monitoring of the strains of girders in a skyscraper) Within the context of this thesis, we present a WSN where the sensors are smart cameras! The study of such a network presents great interest as well as the development of applications based on it.

Made available in DSpace on 2015-04-22T22:00:52Z (GMT). No. of bitstreams: 1 Dissertacao_Alexandre Lopes.pdf: 2105277 bytes, checksum: 2f8d59afe6f1a33f9fb5978e5f6328a7 (MD5) Previous issue date: 2010-07-01 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / This work presents a modular architecture for hardware development and integration of various technologies of wireless communication (Bluetooth, GSM / GPRS and ZigBee) in a gateway for Wireless Sensor Networks (WSNs). Thus, the proposal seeks to address an issue not widely explored in a practical way that is the local and remote collection of data from geographically distributed networks. The objective of this research is to focus on practical technological aspects that allow the integration of different technologies in a practical and real hardware platform. The proposed architecture includes power management and selection of several technologies for wireless communication that will be used according to the application. To validate the proposed architecture case study is carried out in order to present the results achieved during the experiments. / Este trabalho apresenta uma arquitetura modular de hardware para viabilização e integração de diversas tecnologias de comunicação sem fio (Bluetooth, GSM/GPRS e ZigBee) em um gateway para Redes de Sensores Sem Fio (RSSFs). Desta forma, a proposta visa solucionar um problema pouco explorado de forma prática, que consiste na coleta presencial e remota de dados de redes geograficamente distribuídas. O objetivo é concentrar essa investigação em aspectos tecnológicos práticos que permitam a integração de diferentes tecnologias em uma solução prática e real. A arquitetura modular proposta contempla o gerenciamento de energia e a seleção da tecnologia de comunicação sem fio que será utilizada de acordo com a aplicação. Para validação da proposta um estudo de caso é realizado com o intuito de apresentar os resultados alcançados durante os experimentos realizados.

Philosophiae Doctor - PhD / Wireless sensor networks (WSNs) have become a popular research area that is widely gaining the attraction from both the research and the practitioner communities due to their wide area of applications. These applications include real-time sensing for audio delivery, imaging, video streaming, and remote monitoring with positive impact in many fields such as precision agriculture, ubiquitous healthcare, environment protection, smart cities and many other fields. While WSNs are aimed to constantly handle more intricate functions such as intelligent computation, automatic transmissions, and in-network processing, such capabilities are constrained by their limited processing capability and memory footprint as well as the need for the sensor batteries to be cautiously consumed in order to extend their lifetime. This thesis revisits the issue of the energy efficiency in sensor networks by proposing a novel clustering approach for routing the sensor readings in wireless sensor networks. The main contribution of this dissertation is to 1) propose corrective measures to the traditional energy model adopted in current sensor networks simulations that erroneously discount both the role played by each node, the sensor node capability and fabric and 2) apply these measures to a novel hierarchical routing architecture aiming at maximizing sensor networks lifetime. We propose three energy models for sensor network: a) a service-aware model that account for the specific role played by each node in a sensor network b) a sensor-aware model and c) load-balancing energy model that accounts for the sensor node fabric and its energy footprint. These three models are complemented by a load-balancing model structured to balance energy consumption on the network of cluster heads that forms the backbone for any cluster-based hierarchical sensor network. We present two novel approaches for clustering the nodes of a hierarchical sensor network: a) a distance-aware clustering where nodes are clustered based on their distance and the residual energy and b) a service-aware clustering where the nodes of a sensor network are clustered according to their service offered to the network and their residual energy. These approaches are implemented into a family of routing protocols referred to as EOCIT (Energy Optimization using Clustering Techniques) which combines sensor node energy location and service awareness to achieve good network performance. Finally, building upon the Ant Colony Optimization System (ACS), Multipath Routing protocol based on Ant Colony Optimization approach for Wireless Sensor Networks (MRACO) is proposed as a novel multipath routing protocol that finds energy efficient routing paths for sensor readings dissemination from the cluster heads to the sink/base station of a hierarchical sensor network. Our simulation results reveal the relative efficiency of the newly proposed approaches compared to selected related routing protocols in terms of sensor network lifetime maximization.