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 two 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 distanceaware 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.

The work described in this thesis is concerned with self-localisation (automated estimation of sensor locations) and source-localisation (location of a target) using Wireless Sensor Networks (WSNs). The motivation for the research in this thesis is the on-line localisation of marmots from their alarm calls. The application requires accurate 3D self-localisation (within a small percentage of sensor spacing) as well as timely operation. Further challenges are added by the high data-rate involved: sensor nodes acquire data at a rate that is greater than the available network bandwidth. This data cannot be streamed over a multi-hop network, implying a need for data reduction through in-network event detection and local data compression or filtering techniques. The research approach adopted in this thesis combined simulation, emulation and real-life experimentation. Real-life deployment and experimentation highlighted problems that could not be predicted in controlled experiments or simulation. Emulation used data gathered from controlled, real-life experimentation to simulate proposed system refinements; this was sufficient to provide a proof-of-concept validation for some of the concepts developed. Simulation allowed the understanding of underlying theoretical behaviour without involving the complex environmental effects caused by real-life experimentation. This thesis details contributions in two distinct aspects of localisation: acoustic ranging and end-toend deployable acoustic source localisation systems. With regard to acoustic ranging and 3D localisation, two WSN platforms were evaluated: one commercially available, but heavily constrained (Mica2) and one custom-built for accurate localisation (Embedded Networked Sensing Box (ENSBox)). A new proof of concept platform for acoustic sensing (based on the Gumstix single-board computer) was developed by the author (including the implementation of a ranging mechanism), based on experiences with the platforms above. Furthermore, the literature was found to lack a specific procedure for evaluation and comparison of self-localisation algorithms from theoretical conception to real-life testing. Therefore, an evaluation cycle for self-localisation algorithms that encompassed simulation, emulation and real-life deployment was developed. With respect to source localisation, a hardware and software platform named VoxNet was designed and implemented.

Wireless Sensor Networks (WSNs) overcome the difficulties of other monitoring systems, as they require no human attendance on site, provide real-time interaction with events, and maintain cost and power efficient operations. However, further efficiencies are required especially in the case of Outdoor Environment Monitoring (OEM) applications due to their harsh operational conditions, huge targeted areas, limited energy budget, and required Three-Dimensional (3D) setups. A fundamental issue in defeating these practical challenges is the deployment planning of the WSNs. The deployment plan is a key factor of many intrinsic properties of OEM networks, summarized in connectivity, lifetime, fault-tolerance, and cost-effectiveness. In this thesis, we investigate the problem of WSNs deployments that address these properties in order to overcome the unique challenges and circumstances in OEM applications. A natural solution to this problem is to have multiple relay nodes that reserve more energy for sensing, and provide vast coverage area. Furthermore, assuming a subset of these relay nodes are mobile can contribute in repairing the network connectivity problems and recovering faulty nodes, in addition to granting balanced load distributions, and hence prolonging the network lifetime. We investigate this promising research direction by proposing a 3D grid-based deployment planning for heterogeneous WSNs in which Sensor Nodes (SNs) and Relay Nodes (RNs) are efficiently deployed on grid vertices. Towards this efficiency, we analyze and characterize the grid connectivity property in the 3D space. Afterward, we design optimization schemes for the placement of SNs and RNs on the 3D grid models. Based on theoretical analysis and extensive simulations, the proposed schemes show a significant enhancement in terms of network connectivity and lifetime in OEM applications. / Thesis (Ph.D, Computing) -- Queen's University, 2011-05-02 10:29:01.785

Η παρούσα διπλωματική εργασία πραγματεύεται την παρουσίαση των ασύρματων δικτύων αισθητήρων και ελεγκτών στην βιομηχανία. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Γενικής Ηλεκτροτεχνίας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός είναι η δημιουργία μίας ολοκληρωμένης παρουσίασης για την τεχνολογία ασύρματης δικτύωσης σε βιομηχανικό περιβάλλον, ώστε να μπορεί ο αναγνώστης να κατανοήσει εις βάθος τα πλεονεκτήματα αλλά και τους κινδύνους από την εφαρμογή της, να ενημερωθεί σε ποιο επίπεδο εφαρμογής βρίσκεται σήμερα, καθώς και να κατανοήσει το τεχνικό μέρος της τεχνολογίας αυτής. Αρχικά έγινε μία εισαγωγή στο πώς δουλεύει η ασύρματη τεχνολογία και των βασικών χαρακτηριστικών της, (κεραίες τοπολογίες κλπ), ενώ παρουσιάστηκαν και τα διάφορα πρωτόκολλα που χρησιμοποιούνται στα ασύρματα δίκτυα γενικά. Στη συνέχεια έγινε παρουσίαση των απαιτήσεων για βιομηχανική δικτύωση (π.χ. ασφάλεια, αξιοπιστία) ενώ μελετήθηκε πώς μπορεί να γίνει στην πράξη η εφαρμογή των ασυρμάτων δικτύων στον τομέα της βιομηχανίας, δηλαδή τα πρωτόκολλα που χρησιμοποιούνται, καθώς και ανάλυση του τομέα της ασφάλειας δεδομένων κατά την ασύρματη μετάδοση στο βιομηχανικό περιβάλλον. Το επόμενο βήμα έγινε παρουσίαση του λογισμικού Prosoft Wireless Designer της εταιρίας Prosoft για τον σχεδιασμό βιομηχανικών δικτύων σε περιβάλλον υπολογιστή. Τέλος παρουσιάστηκαν επιλεκτικά παραδείγματα υλοποιημένων εφαρμογών ασύρματης δικτύωσης από εταιρίες, καθώς και διάφορα προϊόντα που κυκλοφορούν στην αγορά και χρησιμοποιούνται αποκλειστικά για βιομηχανική ασύρματη δικτύωση. / -

In most of critical infrastructures, Wireless Sensor Networks (WSNs) are deployed due to their low-cost, flexibility and efficiency as well as their wide usage in several infrastructures. Regardless of these advantages, WSNs introduce various security vulnerabilities such as different types of attacks and intruders due to the open nature of sensor nodes and unreliable wireless links. Therefore, the implementation of an efficient Intrusion Detection System (IDS) that achieves an acceptable security level is a stimulating issue that gained vital importance. In this thesis, we investigate the problem of security provisioning in WSNs based critical monitoring infrastructures. We propose a trust based hierarchical model for malicious nodes detection specially for Black-hole attacks. We also present various Machine Learning (ML)-driven IDSs schemes for wirelessly connected sensors that track critical infrastructures. In this thesis, we present an in-depth analysis of the use of machine learning, deep learning, adaptive machine learning, and reinforcement learning solutions to recognize intrusive behaviours in the monitored network. We evaluate the proposed schemes by using KDD'99 as real attacks data-sets in our simulations. To this end, we present the performance metrics for four different IDSs schemes namely the Clustered Hierarchical Hybrid IDS (CHH-IDS), Adaptively Supervised and Clustered Hybrid IDS (ASCH-IDS), Restricted Boltzmann Machine-based Clustered IDS (RBC-IDS) and Q-learning based IDS (QL-IDS) to detect malicious behaviours in a sensor network. Through simulations, we analyzed all presented schemes in terms of Accuracy Rates (ARs), Detection Rates (DRs), False Negative Rates (FNRs), Precision-recall ratios, F_1 scores and, the area under curves (ROC curves) which are the key performance parameters for all IDSs. To this end, we show that QL-IDS performs with ~ 100% detection and accuracy rates.

Τα Wireless Sensor Networks (WSNs) είναι μια σχετικά νέα τεχνολογία, της οποίας η σημαντικότητα έχει αναγνωριστεί από την επιστημονική κοινότητα και έχει προοπτικές για εφαρμογή σε πολλές περιπτώσεις που απαιτείται επίβλεψη και έλεγχος σε μεγάλες εκτάσεις, όπως ο έλεγχος καλής λειτουργίας κτηρίων και κατασκευών, παρακολούθηση στρατιωτικών περιοχών, παρακολούθηση και έλεγχος καλλιεργειών ή ακόμα και επίβλεψη της υγείας ενός ασθενούς. Είναι προφανές πως σε πολλά από αυτά τα σενάρια εφαρμογών τα δεδομένα που αποκτώνται και ανταλλάσσονται μέσα σε αυτά τα δίκτυα είναι ευαίσθητα και η απόκρυψή τους από τρίτους, καθώς και η αποτροπή προσθήκης ψευδών δεδομένων από τρίτους είναι υψίστης σημασίας. Καθώς όμως τα δίκτυα αυτά αποτελούνται από χαμηλής υπολογιστικής δυνατότητας κόμβους, (τόσο λόγω οικονομίας, ώστε, δεδομένου του αριθμού των κόμβων που απαιτούνται για τέτοιες εφαρμογές, το κόστος να κρατηθεί σε λογικά επίπεδα, όσο και για λόγους κατανάλωσης ενέργειας) απαιτείται η χρήση αλγορίθμων ασφαλείας μικρών υπολογιστικών και επικοινωνιακών απαιτήσεων. Για την επίτευξη ασφαλούς επικοινωνίας μεταξύ των κόμβων με μικρή υπολογιστική επιβάρυνση, υλοποιούνται συμμετρικοί αλγόριθμοι κρυπτογραφίας, και για τη διαχείριση των κλειδιών κρυπτογραφίας το πρωτόκολλο διαχείρισης κλειδιών S2RP, το οποίο καθορίζει μεθόδους διανομής, αλλά και ακύρωσης συμμετρικών κλειδιών. Το πρωτόκολλο αυτό μπορεί να διατηρήσει προς τα εμπρός και προς τα πίσω ασφάλεια (ασφάλεια των μελλοντικών μεταδόσεων, και ασφάλεια των δεδομένων που έχουν ήδη μεταδοθεί αντίστοιχα) των δεδομένων σε δυναμικά μεταβαλλόμενες τοπολογίες (πχ. πρόσθεση νέου κόμβου ή ανακάλυψη εκτεθειμένου κόμβου που πρέπει να αφαιρεθεί από την τοπολογία). Στο πλαίσιο της εργασίας, έγινε υλοποίηση του πρωτοκόλλου S2RP, καθώς και κρυπτογραφικών αλγορίθμων που απαιτούνται για την εφαρμογή του. Η υλοποίηση έγινε αρχικά σε ένα γραφικό περιβάλλον εξομοίωσης, που δημιουργήθηκε για τον έλεγχο του πρωτοκόλλου σε επίπεδο πακέτου, ενώ στη συνέχεια έγινε μεταφορά του πρωτοκόλλου σε δίκτυο από ασύρματους αισθητήρες TelosB. / Wireless Sensor Networks (WSNs) are a relatively new technology, the importance of which is widely recognized in academia. They have great potential for use in applications requiring monitoring and control over large areas, like integrity and operational monitoring of buildings and structures, military surveillance, crop monitoring or even health monitoring. It is obvious that the data transfered in most of these applications are of a sensitive nature, and preventing a third party from accessing that data, or injecting its own forged data in the network is of utmost importance. However, because of the low computational power and network performance of these networks' nodes (which is due to economic reasons - so as to keep cost in reasonable levels in high node count networks, as well as for energy consumption reasons), the use of algorithms and protocols of low computational and communication requirements is mandatory. To achieve secure communication between the nodes of a such network, we implement symmetric key cryptographic algorithms, and the protocol S2RP (Secure and Scalable Rekeying Protocol) for key management. S2RP defines procedures for key distribution and revocation, with the use of which it can maintain forward and backward communication security (e.g. connection of a new node, or discovery of an exposed node, which must be removed) for dynamic network topologies. For the purpose of this thesis, we implemented the S2RP protocol, as well as the additional cryptographic primitives that are needed to achieve secure communication in a network. The implementation was initially made within a graphical simulator, which we implemented to test the protocol in the packet level. Finally, we ported the protocol to a network of TelosB motes.

Στη παρούσα διπλωματική εργασία ασχολούμαστε με την ανάπτυξη τεχνικών για υλοποίηση ενός κατανεμημένου φίλτρου Kalman σε ένα Δίκτυο Αισθητήρων (WSN). Τα δίκτυα αυτά έχουν γνωρίσει τα τελευταία χρόνια ραγδαία ανάπτυξη λόγω των εξαιρετικά πολλών εφαρμογών τους σε διάφορα πεδία της ανθρώπινης δραστηριότητας. Το πρόβλημα που πραγματευόμαστε εδώ είναι η προσπάθεια εκτίμησης της κατάστασης μιας στοχαστικής διαδικασίας που επιτηρείται-παρακολουθείται απο το δίκτυο. Οι κόμβοι-αισθητήρες που συναπαρτίζουν αυτά τα δίκτυα έχουν συνήθως περιορίσμενες δυνατότητες ¨αίσθησης¨, πράγμα που σημαίνει ότι κάθε μεμονωμένος κόμβος αδυνατεί να παράξει μια καλή εκτίμηση της κατάστασης. Διάφορες τεχνικές εχούν προταθεί για την επίλυση τέτοιου είδους προβλημάτων όπως το κεντρικό Φίλτρο Kalman ή διάφορες αποκεντρωμένες προσεγγίσεις, οι οποιές είχαν όμως υψηλό υπολογιστικό κόστος και τις καθιστούσαν πρακτικά μη υλοποιήσιμες, ειδικά για δίκτυα με μεγάλο αριθμό κόμβων. Έτσι στη παρούσα εργασία , χρησιμοποιώντας ως εργαλείο την θεώρια των αλγορίθμων ¨Κοινής Συμφωνίας¨ (Consensus Algorithms) , κατασκευάζουμε Αλγορίθμους χαμήλης πολυπλοκότητας, για την υλοποίηση ενός Kατανεμημένου Φίλτρου Kalman, θεωρώντας ότι όλοι οι κόμβοι είναι ομότιμοι (peer-to-peer αρχιτεκτονικές), κάθε κόμβος επικοινωνεί μόνο με τους γειτονικούς του και δεν υπάρχουν Fusion Centers. Παρουσιάζουμε έτσι τρεις διαφορετικούς επαναληπτικούς αλγορίθμους βασιζομένων σε δύο διαφορετικές λογικές και τέλος προσομοιώνουμε και αξιολογούμε την επίδοση καθενός από αυτούς. / In this thesis we deal with the development of techniques for implementing a distributed Kalman filter in a sensor network (WSN). Ιn recent years these networks have experienced rapid growth, due to the numerous applications in various fields of human activity. The problem we discuss here is the attempt to estimate the state of a stochastic process which is monitored by nodes-sensors. The nodes that constitute these networks usually have limited “sense” capabilities, which means that each node is unable to produce a good estimate of the state, using only its own measurements. Various techniques have been proposed to solve this kind of problems, such as the Central Kalman Filter or several decentralized approaches, which did have a high computational cost that renders them impractical, especially for networks with a high number of nodes. Thus, in the present work, , we construct low complexity algorithms for the implementation of a Distirbuted Kalman Filter, using as a tool the theory of Consensus Algorithms and assuming that all nodes are peers (peer-to-peer architectures), each node communicates only with its neighboring and no Fusion Centers exist. Τhus, we present three different iterative algorithms based on two different approaches and finally simulate and evaluate the performance of each of them.

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.

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.