Sensor failures or oversupply in wireless sensor networks (WSNs), especially initial random deployment, create both spare sensors (whose area is fully covered by other sensors) and sensing holes. We envision a team of robots to relocate sensors and improve their area coverage. Existing algorithms, including centralized ones and the only localized G-R3S2, move only spare sensors and have limited improvement because non-spare sensors, with area coverage mostly overlapped by neighbour sensors, are not moved, and additional sensors are deployed to fill existing holes. We propose a localized algorithm, called Localized Ant-based Sensor Relocation Algorithm with Greedy Walk (LASR-G), where each robot may carry at most one sensor and makes decision that depends only on locally detected information. In LASR-G, each robot calculates corresponding pickup or dropping probability, and relocates sensor with currently low coverage contribution to another location where sensing hole would be significantly reduced. The basic algorithm optimizes only area coverage, while modified algorithm includes also the cost of robot movement. We compare LASR-G with G-R3S2, and examine both single robot and multi robots scenarios. The simulation results show the advantages of LASR-G over G-R3S2.

Secure wireless communications among sensor nodes is critical to the deployment of wireless sensor networks. However, resource limited sensor nodes cannot afford complex cryptographic algorithms. In this thesis, we propose a low complexity and energy efficient reconfigurable feedback shift register (RFSR) stream cipher, link layer encryption framework RSec and authentication protocol RAuth. RFSR adds one new dimension, reconfigurable cipher structure, to the existing stream ciphers. The proposed RFSR is implemented on a field programmable gate array platform. Simulation results show that much lower power consumption, delay and transmission overhead are achieved compared to the existing microprocessor based cipher implementations. The RSec framework utilizes RFSR ciphers to guarantee message confidentiality. By comparing with other encryption frameworks in terms of energy efficiency, RSec achieves the best benchmark. The RAuth protocol is designed on top of RFSR and RSec. It provides excellent authentication speed and security level by comparing with other authentication protocols. / Graduate / 0544 / 0984 / zggyzz@gmail.com

Wireless sensor networks (WSNs) are a valuable technology to support a huge range of applications spanning from military to commercial, such as battlefield surveillance, habitat monitoring, forest fire detection, disaster salvage, and inventory control management. It has the capability to reveal previously unobservable phenomena in the physical world and significant flexibility of installation and manipulation. The major challenges of WSNs design come from the requirements of energy constraint, distributed control and scalability. In this thesis we studied three topics on WSNs. The first one was energy-efficient medium access control (MAC) protocol design. We proposed a MAC protocol which schedules the send and receive times for all nodes within the network. As all nodes only wake up when they send or receive, significant energy is saved by reducing idle listening, collisions and overhearing. And we evaluated the protocol performance by using the GloMoSim simulator. The second topic was about distributed transmission power control of wireless sensor nodes. We proposed a simple scheme which employs request-to-send (RTS) and clear-to-send (CTS) frames to exchange channel gain information, based on which concurrent senders determine their own transmission power without a central controller to coordinate them. Simulation results showed that our scheme can save 30% to 50% of the energy, and also reduce transmissionlatency.The third topic was on event detection. Due to the fact that wireless sensor nodes are spatially distributed throughout the area of interest, this application has to been implemented in distributed form. We proposed a scheme which does not need a pre-designated fusion node, and this greatly improves network scalability. We provided close-form expressions to estimate the probabilities of detection failure and false alarm, and validated them by extensive simulation.

In wireless sensor network, we usually need to combine the information gathered from multiple sensors to detect an event. To answer this question we present a new type of query, Geo-Range query. This query reports the geographic points where the average value of nearby sensors are greater than certain threshold. To perform this query, we developed two fast, efficient algorithms. The Brute-Force algorithm use exhaustive method to enumerate all possible values, which takes O(n^3) running time. The Sweep-Line algorithm applies a conceptual line sweeping through the plane. The sweep-line moves through the plane and keeps tracking all the sensor points encountered. The algorithm takes O( n^2 \log n ) running time, while it still gives exact solution to the problem. We implement and simulate our algorithms in Visual Basic.Net.

Wireless sensor network plays a significant role in the design of future Smart Grid, mainly for the purpose of environment monitoring, data acquisition and remote control. Sensors deployed on the utility poles on the power transmission line are used to collect environment information and send them to the substations for analysis and management. However, the transmission is suffered from erasures and errors along the transmission channels. In this thesis, we consider a line network model proposed in [1] and [2]. We first analyze several different erasure codes in terms of overhead and encoding/decoding costs, followed by proposing two different coding schemes for our line network. To deal with both erasures and errors, we combine the erasure codes and the traditional error control codes, where an RS code is used as an outer codes in addition to the erasure codes. Furthermore, an adaptive RS coding scheme is proposed to improve the overall coding efficiency over all SNR regions. In the end, we apply network coding with error correction of network errors and erasures and examine our model from the mathematical perspective. / Graduate

Secure wireless communications among sensor nodes is critical to the deployment of wireless sensor networks. However, resource limited sensor nodes cannot afford complex cryptographic algorithms. In this thesis, we propose a low complexity and energy efficient reconfigurable feedback shift register (RFSR) stream cipher, link layer encryption framework RSec and authentication protocol RAuth. RFSR adds one new dimension, reconfigurable cipher structure, to the existing stream ciphers. The proposed RFSR is implemented on a field programmable gate array platform. Simulation results show that much lower power consumption, delay and transmission overhead are achieved compared to the existing microprocessor based cipher implementations. The RSec framework utilizes RFSR ciphers to guarantee message confidentiality. By comparing with other encryption frameworks in terms of energy efficiency, RSec achieves the best benchmark. The RAuth protocol is designed on top of RFSR and RSec. It provides excellent authentication speed and security level by comparing with other authentication protocols. / Graduate / 0544 / 0984 / zggyzz@gmail.com

Τα κυψελικά αυτόματα (ΚΑ) αποτελούν την εξιδανίκευση ενός φυσικού συστήματος όπου ο χώρος και ο χρόνος είναι διακριτοί και οι φυσικές ποσότητες λαμβάνουν μόνο ένα πεπερασμένο σύνολο τιμών. Τα κυψελικά αυτόματα αποτελούνται από ένα πλέγμα με διακριτούς πανομοιότυπους κόμβους. Κάθε σημείο-κόμβος του πλέγματος χαρακτηρίζεται από μία τιμή η οποία δεν είναι αυθαίρετη, αλλά λαμβάνεται από ένα συγκεκριμένο σύνολο ‘επιτρεπτών’ ακέραιων τιμών. Οι τιμές αυτών των κόμβων του πλέγματος εξελίσσονται από τη μία χρονική στιγμή στην άλλη σύμφωνα με προκαθορισμένους τοπικούς κανόνες. Η συνολική δομή αποτελεί ένα μοντέλο παράλληλου υπολογισμού. ΄Οταν η απλή δομή του μοντέλου επαναλαμβάνεται, προκύπτουν πολύπλοκα πρότυπα που μπορούν να προσομοιώσουν ποικίλα πολύπλοκα φυσικά φαινόμενα και συστήματα. Χρησιμοποιούμε τα κυψελικά αυτόματα για να προσομοιώσουμε έναν αλγόριθμο ελέγχου τοπολογίας για ασύρματα δίκτυα αισθητήρων. Τα ασύρματα δίκτυα αισθητήρων αποτελούνται από ένα μεγάλο αριθμό διασκορπισμένων αισθητήρων-κόμβων που λειτουργούν με μπαταρίες. Σκοπός του προβλήματος ελέγχου τοπολογίας σε ασύρματα δίκτυα αισθητήρων είναι η επιλογή κατάλληλου υποσυνόλου κόμβων ικανών να παρακολουθούν μια περιοχή με στόχο τη μικρότερη δυνατή κατανάλωση ενέργειας και ως εκ τούτου την επέκταση της διάρκειας ζωής του δικτύου. / Cellular automata (CA) are an idealization of a physical system where space and time are discrete and the physical quantities take only a finite set of values. Cellular automata consist of a regular grid of identical cells-nodes. Each node is characterized by a non arbitrary value selected by a specific set of appropriate integers. The values of the nodes change over time according to predefined localized rules. The overall structure can be viewed as a parallel processing device. This simple structure when iterated several times produces complex patterns displaying the potential to simulate different sophisticated natural phenomena. We use cellular automata for simulating a topology control algorithm in Wireless Sensor Networks (WSNs). WSNs are composed of a large number of distributed sensor nodes operating on batteries; the objective of the topology control problem in WSNs is to select an appropriate subset of nodes able to monitor a region at a minimum energy consumption cost thus extending the network lifetime.

Este trabalho avalia o desempenho de um controlador fuzzy (tipo Takagi-Sugeno-Kang) quando, utilizando tecnologia sem fio para conectar as entradas e a saída do controlador aos sensores/atuadores, sofre perda das informações destes canais, resultado de perdas de pacotes. Tipicamente são utilizados controladores PID nas malhas de controle. Assim, o estudo realizado compara os resultados obtidos com os controladores fuzzy com os resultados dos controladores PID. Além disso, o trabalho visa estudar o comportamento deste controlador implementado em uma arquitetura microprocessada utilizando números inteiros nos cálculos, interpolação com segmentos de reta para as funções de pertinência da entrada e singletons nas funções de pertinência da saída. Para esse estudo foi utilizado, num ambiente Matlab/Simulink, um controlador fuzzy e o aplicativo True Time para simular o ambiente sem fio. Desenvolvido pelo Departamento de Controle Automático da Universidade de Lund, o True Time é baseado no Matlab/Simulink e fornece todas as ferramentas necessárias para a criação de um ambiente de rede (com e sem fio) virtual. Dado o paradigma de que quanto maior for a utilização do canal, maior a degradação do mesmo, é avaliado o comportamento do sistema de controle e uma proposta para diminuir o impacto da perda de pacotes no controle do sistema, bem como o impacto da variação das características internas da planta e da arquitetura utilizada na rede. Inicialmente são realizados ensaios utilizando-se o controlador fuzzy virtual (Simulink) e, posteriormente, o controlador implementado com dsPIC. Ao final, é apresentado um resumo desses ensaios e a comprovação dos bons resultados obtidos com um controlador fuzzy numa malha de controle utilizando uma rede na entrada e na saída do controlador. / This work evaluates the performance of a fuzzy controller (Takagi-Sugeno-Kang) that uses wireless technology to connect the inputs and the output of the controller to sensors / actuators, and with the loss of information from these channels, the result of packet loss. PID controllers are typically used in control loops. Thus, the study compares the results obtained with the fuzzy controllers with the results of PID controllers. Moreover, the work aims to study the behavior of this controller implemented in a microprocessor architecture using integer calculations, interpolation with straight line segments for the membership functions of input and singletons in the output membership functions. For this study it was used in a Matlab/Simulink, a fuzzy controller and the application True Time to simulate wireless environment (Developed by the Department of Automatic Control at Lund University). It is based on MATLAB/Simulink and provides all the tools necessary to create a virtual network environment (wired and wireless). When we increase the occupation of the channel we increase the degradation of it. Under this conditions, is rated the behavior of the control system and is evaluated, and actions were proposal to reduce the impact of packet loss in the control system, as well as the impact of variations in the internal characteristics of plant and architecture used in the network. Initially, tests are conducted using the virtual fuzzy controller (Simulink ) and thereafter, the controller implemented with dsPIC. Finally, a summary of testing and verification of results are presented.

Nos recherches se situent à l'intersection des sphères académiques et industrielles et des organismes de standardisation pour permettre la mise en place d'un Internet des objets (IoT) sécurisé et efficace.Nous étudions des solutions de sécurisation en parcourant les standards de manière ascendante.En premier lieu, nous constatons que l'accélération matérielle des algorithmes de cryptographie est nécessaire pour les équipements formant l'IoT car il permet une reduction de deux ordres de grandeur des durées de calcul.Le surcoût des opérations cryptographiques n'est cependant qu'un des facteurs qui gouverne la performance globale dans le contexte des systèmes en réseau.Nous montrons à travers l'implementation d'applications pratiques que les dispositifs de sécurité de la couche 2 n'augmentent que de quelques pourcents la dépense énergétique totale.Ceci est acceptable, même pour les systèmes les plus contraints, comme ceux utilisant la recuperation d'énergie ambiante.La sécurité de la couche 2 contraint de faire confiance à chacun des noeuds du chemin de communication comprenant potentiellement des éléments malveillants, nous devons donc protéger le flux de données par un mécanisme de bout en bout.Nous étudions le protocole DTLS, standard de l'IETF pour la sécurité de l'IoT.Nous contribuons aux discussions sur l'intérêt de DTLS dans les environnements contraints, à la fois dans les organismes de standardisation et de recherche.Nous évaluons DTLS de manière étendue avec différents réseaux à cycle d'activité ou duty cycle au travers d'expérimentations, d'émulations et d'analyses.De manière surprenante, nos résultats démontrent la très faible performance de DTLS dans ces réseaux où l'efficacité énergétique est primordiale.Comme un client et un serveur DTLS échangent beaucoup de paquets de signalisation, la connection DTLS prends entre quelques secondes et quelques dizaines de secondes, ceci pour plusieurs des protocoles étudiés.DTLS a été conçu pour les communications de bout en bout dans l'Internet classique, contrairement au nouveau protocol CoAP qui lui est destiné à des machines contraintes en facilitant le traffic asynchrone, les communications de groupe et le besoin de stockage intermédiaire.Donc, en plus du problème de performance, l'architecture de sécurité basée sur DTLS n'est pas capable de répondre aux contraintes de ces dispositifs et CoAP devient inutilisable.Nous proposons une architecture qui s'appuie à la fois sur une approche centrée sur le contenu et sur la notion classique de connection.L'échange des clefs est fait à travers des canaux sécurisés établis par DTLS, mais la notion d'états entre les entités de communication est supprimée grâce au concept d'objets sécurisés.Le mécanisme proposé resiste aux attaques par rejeu en regroupant les capacités de controle d'accès avec les en-tetes de communication CoAP.OSCAR, notre architecture à objets sécurisés, supporte intrinsèquement les communications de groupe et le stockage intermédiaire, sans perturber le fonctionnement à cycle d'activité de la radio des équipements contraintes.Les idées d'OSCAR sont discutés par les groupes de standardisation de l'Internet en vue d'être intégrées dans les standards à venir. / Our research explores the intersection of academic, industrial and standardization spheres to enable secure and energy-efficient Internet of Things. We study standards-based security solutions bottom-up and first observe that hardware accelerated cryptography is a necessity for Internet of Things devices, as it leads to reductions in computational time, as much as two orders of magnitude. Overhead of the cryptographic primitives is, however, only one of the factors that influences the overall performance in the networking context. To understand the energy - security tradeoffs, we evaluate the effect of link-layer security features on the performance of Wireless Sensors Networks. We show that for practical applications and implementations, link-layer security features introduce a negligible degradation on the order of a couple of percent, that is often acceptable even for the most energy-constrained systems, such as those based on harvesting.Because link-layer security puts trust on each node on the communication path consisted of multiple, potentially compromised devices, we protect the information flows by end-to-end security mechanisms. We therefore consider Datagram Transport Layer Security (DTLS) protocol, the IETF standard for end-to-end security in the Internet of Things and contribute to the debate in both the standardization and research communities on the applicability of DTLS to constrained environments. We provide a thorough performance evaluation of DTLS in different duty-cycled networks through real-world experimentation, emulation and analysis. Our results demonstrate surprisingly poor performance of DTLS in networks where energy efficiency is paramount. Because a DTLS client and a server exchange many signaling packets, the DTLS handshake takes between a handful of seconds and several tens of seconds, with similar results for different duty cycling protocols.But apart from its performance issues, DTLS was designed for point-to-point communication dominant in the traditional Internet. The novel Constrained Ap- plication Protocol (CoAP) was tailored for constrained devices by facilitating asynchronous application traffic, group communication and absolute need for caching. The security architecture based on DTLS is, however, not able to keep up and advanced features of CoAP simply become futile when used in conjunction with DTLS. We propose an architecture that leverages the security concepts both from content-centric and traditional connection-oriented approaches. We rely on secure channels established by means of DTLS for key exchange, but we get rid of the notion of “state” among communicating entities by leveraging the concept of object security. We provide a mechanism to protect from replay attacks by coupling the capability-based access control with network communication and CoAP header. OSCAR, our object-based security architecture, intrinsically supports caching and multicast, and does not affect the radio duty-cycling operation of constrained devices. Ideas from OSCAR have already found their way towards the Internet standards and are heavily discussed as potential solutions for standardization.

This research concerns the in-use performance of light-gauge steel modular construction used for residential purposes. The aim was to investigate ways to reduce the in-use energy consumption of new buildings, while ensuring thermal comfort. Data were collected from two case study buildings in the UK, one in Loughborough and the other in London, using a variety of methods including building measurement, building monitoring, inspections, and a detailed review of the construction documentation. The case study buildings were monitored using EnOcean enabled wireless sensor networks and standalone temperature sensors. Monitoring data included electricity consumption in individual rooms, often by end use, space heating use, internal temperature and relative humidity, and external temperature. Building measurements included blower door tests to measure fabric air leakage rates, infrared thermal imaging to identify fabric defects and weaknesses, and ventilation system flowrate measurements. Inspections and the review of documentation allowed problems with design, manufacture and construction to be identified. A particular concern for thermally lightweight construction is the risk of overheating, therefore overheating analyses were undertaken. The research identified weaknesses in the design, construction and operation of the case study buildings resulting in increased energy use and poor thermal comfort, particularly overheating. The modular construction studied requires specific design changes to improve the fabric and building services, in order to reduce energy use. There are also specific recommendations for quality control on site to ensure critical stages are correctly completed, such as installing rigid insulation. There are also more general recommendations for how a company operates because this can influence performance; there ought to be greater attention to holistic design and greater collaboration with suppliers and contractors to determine robust solutions. Overheating was a problem in the London case study, and more research is required to understand the scale of the problem. Avoidance of overheating must be a focus in the design of new buildings. The findings suggest that once the problems with the design and quality control on site are rectified, offsite modular construction can be used to consistently and reliably provide low energy homes.