Recent surveys on medical service systems show that the cost of patient monitoring has grown significantly. The widespread use of portable digital medical device makes it possible to provide a more comprehensive tracking of patient conditions. However, the development of a full scale, distributed health monitoring system is much delayed due to the lack of efficient wireless communication in a large distributed network. This becomes a challenging research topic which is to find a way to provide accurate and real time patient information to medical experts in a fast, efficient and cost effective fashion. This paper proposes a novel solution on building a system which links patients and doctors together using embedded system technology and wireless sensor network. The content presented in this thesis introduces the design and implement of such a system.

Creating a secure wireless sensor network involves authenticating and encrypting messages that are sent throughout the network. The communicating nodes must agree on secret keys in order to be able to encrypt packets. Sensor networks do not have many resources and so, achieving such key agreements is a difficult matter. Many key agreement schemes like Diffie-Hellman and public-key based schemes are not suitable for wireless sensor networks. Pre-distribution of secret keys for all pairs of nodes is not viable due to the large amount of memory used when the network size is large. We propose a novel key management system that works with the random key pre-distribution scheme where deployment knowledge is unknown. We show that our system saves users from spending substantial resources when deploying networks. We also test the new system’s memory usage, and security issues. The system and its performance evaluation are presented in this thesis.

As redes de sensores sem fio (RSSF) são uma tecnologia que ganhou muita importância nos últimos anos. Dentro das diversas aplicações para essas redes, o rastreamento de alvos é considerado essencial. Nessa aplicação, a RSSF deve determinar, de forma colaborativa, a trajetória de um ou mais alvos que se encontrem dentro de sua área de cobertura. O presente trabalho apresenta um algoritmo colaborativo baseado na fatoração multifrontal QR para estimação de trajetórias de alvos com RSSF. A solução proposta está inserida no âmbito da estimação por lotes, na qual os dados são coletados pelos sensores durante a aplicação e só no final é realizada a estimativa da trajetória do alvo. Uma vez coletados os dados, o problema pode ser modelado como um sistema de equações sobredeterminado Ax = b cuja característica principal é ser esparso. A solução desse sistema é dada mediante o método de mínimos quadrados, no qual o sistema é transformado num sistema triangular superior, que é solucionado mediante substituição inversa. A fatoração multifrontal QR é ideal neste contexto devido à natureza esparsa da matriz principal do sistema. A fatoração multifrontal QR utiliza um grafo denominado árvore de eliminação para dividir o processo de fatoração de uma matriz esparsa em fatorações densas de pequenas submatrizes denominadas matrizes frontais. Mapeando a árvore de eliminação na RSSF consegue-se que essas fatorações densas sejam executadas pelos nós sensoriais que detectaram o alvo durante seu trajeto pela rede. Dessa maneira, o algoritmo consegue realizar a fatoração da matriz principal do problema de forma colaborativa, dividindo essa tarefa em pequenas tarefas que os nós de sensoriais da rede possam realizar. / Wireless Sensor Networks (WSN) is a technology that have gained a lot of importance in the last few years. From all the possible applications for WSN, target tracking is considered essential. In this application, the WSN has to determine, in a collaborative way, the trajectory of one or more targets that are within the sensing area of the network. The aim of this document is to present a collaborative algorithm based on multifrontal QR factorization for the solution of the target trajectory estimation problem with WSN. This algorithm uses a batch estimation approach, which assumes that all sensing data are available before the estimation of the target trajectory. If all the observations of the target trajectory is available, the problem can be modeled as an overdetermined system of equations Ax = b where A is sparse. This system of equations is solved by least squares method. The multifrontal QR factorization uses a tree graph called elimination tree to reorganize the overall factorization of a sparse matrix into a sequence of partial factorizations of dense smaller matrices named frontal matrices. By mapping the elimination tree into the WSN, the sensor nodes that observed the target can factorize the frontal matrices. In this manner, the WSN factorizes the matrix A in a collaborative way, dividing the work in small tasks that the sensor nodes could execute.

Many domains, such as geographical and biological sciences, can benefit from the ability of wireless sensor networks to provide long term, high temporal and spatial resolution sensing. Such networks must be able to trade off various requirements against each other to extend network lifetime while still providing useful, good quality data. The challenges faced by equipment in the field can very unpredictable and therefore a wireless sensor network should be able to cope with these challenges and return to a balanced state. Using readily available, low-cost components, this work was inspired by the human endocrine systems ability to maintain homeostasis, or balance, in a large number of parameters simultaneously. This work developed a number of endocrine inspired methods. These were aimed both at improving the power usage of nodes in a wireless sensor network and improving the quality of the data collected. Methods for improving power consumption and data quality were achieved. These methods were successfully deployed, for the purposes of environmental monitoring on a mesh network consisting of 20 nodes, for a period of almost 6 months. Analysis showed that the use of power by individual nodes was improved and that the endocrine inspired methods, aimed at improving data quality, were successful. Node lifetimes were extended, duplicate data reduced and the quality of data improved. The use of low-cost, readily available components was largely successful, and challenges and changes to these components were discussed.

Wireless sensor networks used to have a main role as a monitoring tool for environmental purposes and animal tracking. This spectrum of applications, however, has dramatically grown in the past few years. Such evolution means that what used to be application-specific networks are now multi application environments, often with federation capabilities. This shift results in a challenging environment for data privacy, mainly caused by the broadening of the spectrum of data access points and involved entities. This thesis first evaluates existing privacy preserving data aggregation techniques to determine how suitable they are for providing data privacy in this more elaborate environment. Such evaluation led to the design of the set difference attack, which explores the fact that they all rely purely on data aggregation to achieve privacy, which is shown through simulation not to be suitable to the task. It also indicates that some form of uncertainty is required in order to mitigate the attack. Another relevant finding is that the attack can also be effective against standalone networks, by exploring the node availability factor. Uncertainty is achieved via the use of differential privacy, which offers a strong and formal privacy guarantee through data perturbation. In order to make it suitable to work in a wireless sensor network environment, which mainly deals with time-series data, two new approaches to address it have been proposed. These have a contrasting effect when it comes to utility and privacy levels, offering a flexible balance between privacy and data utility for sensed entities and data analysts/consumers. Lastly, this thesis proposes a framework to assist in the design of privacy preserving data aggregation protocols to suit application needs while at the same time complying with desired privacy requirements. The framework's evaluation compares and contrasts several scenarios to demonstrate the level of flexibility and effectiveness that the designed protocols can provide. Overall, this thesis demonstrates that data perturbation can be made significantly practical through the proposed framework. Although some problems remain, with further improvements to data correlation methods and better use of some intrinsic characteristics of such networks, the use of data perturbation may become a practical and efficient privacy preserving mechanism for wireless sensor networks.

This thesis contributes toward the design of a reliable and energy-efficient transport system for Wireless Sensor Networks. Wireless Sensor Networks have emerged as a vital new area in networking research. In many Wireless Sensor Network systems, a common task of sensor nodes is to sense the environment and send the sensed data to a sink node. Thus, the effectiveness of a Wireless Sensor Network depends on how reliably the sensor nodes can deliver their sensed data to the sink. However, the sensor nodes are susceptible to loss for various reasons when there are dynamics in wireless transmission medium, environmental interference, battery depletion, or accidentally damage, etc. Therefore, assuring reliable data delivery between the sensor nodes and the sink in Wireless Sensor Networks is a challenging task. The primary contributions of this thesis include four parts. First, we design, implement, and evaluate a cross-layer communication protocol for reliable data transfer for data streaming applications in Wireless Sensor Networks. We employ reliable algorithms in each layer of the communication stack. At the MAC layer, a CSMA MAC protocol with an explicit hop-by-hop Acknowledgment loss recovery is employed. To ensure the end-to-end reliability, the maximum number of retransmissions are estimated and used at each sensor node. At the transport layer, an end-to-end Negative Acknowledgment with an aggregated positive Acknowledgment mechanism is used. By inspecting the sequence numbers on the packets, the sink can detect which packets were lost. In addition, to increase the robustness of the system, a watchdog process is implemented at both base station and sensor nodes, which enable them to power cycle when an unexpected fault occurs. We present extensive evaluations, including theoretical analysis, simulations, and experiments in the field based on Fleck-3 platform and the TinyOS operating system. The designed network system has been working in the field for over a year. The results show that our system is a promising solution to a sustainable irrigation system. Second, we present the design of a policy-based Sensor Reliability Management framework for Wireless Sensor Networks called SRM. SRM is based on hierarchical management architecture and on the policy-based network management paradigm. SRM allows the network administrators to interact with the Wireless Sensor Network via the management policies. SRM also provides a self-control capability to the network. This thesis restricts SRM to reliability management, but the same framework is also applicable for other management services by providing the management policies. Our experimental results show that SRM can offer sufficient reliability to the application users while reducing energy consumption by more than 50% compared to other approaches. Third, we propose an Energy-efficient and Reliable Transport Protocol called ERTP, which is designed for data streaming applications in Wireless Sensor Networks. ERTP is an adaptive transport protocol based on statistical reliability that ensures the number of data packets delivered to the sink exceeds the defined threshold while reducing the energy consumption. Using a statistical reliability metric when designing a reliable transport protocol guarantees the delivery of adequate information to the users, and reduces energy consumption when compared to the absolute reliability. ERTP uses hop-by-hop Implicit Acknowledgment with a dynamically updated retransmission timeout for packet loss recovery. In multihop wireless networks, the transmitter can overhear a forwarding transmission and interpret it as an Implicit Acknowledgment. By combining the statistical reliability and the hop-by-hop Implicit Acknowledgment loss recovery, ERTP can offer sufficient reliability to the application users with minimal energy expense. Our extensive simulations and experimental evaluations show that ERTP can reduce energy consumption by more than 45% when compared to the state-of- the-art protocol. Consequently, sensor nodes are more energy-efficient and the lifespan of the unattended Wireless Sensor Network is increased. In Wireless Sensor Networks, sensor node failures can create network partitions or coverage loss which can not be solved by providing reliability at higher layers of the protocol stack. In the final part of this thesis, we investigate the problem of maintaining the network connectivity and coverage when the sensor nodes are failed. We consider a hybrid Wireless Sensor Network where a subset of the nodes has the ability to move at a high energy expense. When a node has low remaining energy (dying node) but it is a critical node which constitutes the network such as a cluster head, it will seek a replacement. If a redundant node is located in the transmission range of the dying node and can fulfill the network connectivity and coverage requirement, it can be used for substitution. Otherwise, a protocol should be in place to relocate the redundant sensor node for replacement. We propose a distributed protocol for Mobile Sensor Relocation problem called Moser. Moser works in three phases. In the first phase, the dying node determines if network partition occurs, finds an available mobile node, and asks for replacement by using flooding algorithm. The dying node also decides the movement schedule of the available mobile node based on certain criteria. The second phase of the Moser protocol involves the actual movement of the mobile nodes to approach the location of the dying node. Finally, when the mobile node has reached the transmission of the dying node, it communicates to the dying nodes and moves to a desired location, where the network connectivity and coverage to the neighbors of the dying nodes are preserved.

<p>Shooter localization systems are used to detect and locate the origin of gunfire. A wireless sensor network is one possible implementation of such a system. A wireless sensor network is sensitive to synchronization errors. Localization techniques that rely on the timing will give less accurate or even useless results if the synchronization errors are too large.</p><p>This thesis focuses on the influence of synchronization errors on the abilityto localize a shooter using a wireless sensor network. A localization algorithm</p><p>is developed and implemented and the effect of synchronization errors is studied. The localization algorithm is evaluated using numerical experiments, simulations, and data from real gunshots collected at field trials.</p><p>The results indicate that the developed localization algorithm is able to localizea shooter with quite good accuracy. However, the localization performance is to a high degree influenced by the geographical configuration of the network as well as the synchronization error.</p> / <p><p>Skottlokaliseringssystem används för att upptäcka och lokalisera ursprunget för avlossade skott. Ett trådlöst sensornätverk är ett sätt att utforma ett sådant system.Trådlösa sensornätverk är känsliga för synkroniseringsfel. Lokaliseringsmetoder som bygger på tidsobservationer kommer med för stora synkroniseringsfel ge dåliga eller helt felaktiga resultat.</p><p>Detta examensarbete fokuserar på vilken inverkan synkroniseringsfel har på möjligheterna att lokalisera en skytt i ett trådlöst sensornätverk. En lokaliseringsalgoritm utvecklas och förmågan att korrekt lokalisera en skytt vid olika synkroniseringsfel undersöks. Lokaliseringsalgoritmen prövas med numeriska experiment, simuleringar och även för data från riktiga skottljud, insamlade vid fältförsök.</p><p>Resultaten visar att lokaliseringsalgoritmen fungerar tillfredställande, men att lokaliseringsförmågan till stor del påverkas av synkroniseringsfel men även av sensornätverkets geografiska utseende.</p></p>

<p>In recent years, the development of wireless sensor networks has made a great progress. Early projects focused on replacement of existing systems equipped with wires. These systems started out as simple static data collection networks with one smart central node that could decide further actions based on the content of the collected data. Through time, the intelligence has become more decentralized, which means the nodes now can cooperate in a more efficient and dynamic manner. The task given is to evaluate TinyOS and NesC on specific hardware from Crossbow Technology Inc, applied on an application called the Open Secure Office Project. This application is designed to enhance the security without negative effects on comfort in a frequently visited open-plan office. Finally, a real world system demonstration should be performed. We propose a solution where there is no urgent need to cover the entire office area with radio signals to maintain a secure sensor system. This is true as long as all entries and exits to the office area are “guarded” by some base station which has as main task to keep track of people and equipment entering or leaving the office. Small scale tests have been performed which show that it is possible to easily develop and maintain a wireless sensor network security system, that could be coordinated by alternative systems.</p>

<p>Wireless sensor networks offer easy implementation, flexibility and mobility of hand held </p><p>devices. Sensors consist of an internal power source, which is the great limitation for </p><p>the life time and the usage of sensor networks. To increase the life time, sensors should </p><p>stay in energy saving sleep mode as long as possible, because in sleep mode the radio is </p><p>either shut down or working with less energy. Better energy handling is implemented in </p><p>different power saving mechanism of common Medium Access Control protocols, which are </p><p>evaluated and analyzed and further extensions and ideas to improve the energy efficiency </p><p>are presented. Slotted PSM is simulated with the NS2 and compared to the WLAN 802.11 </p><p>PSM technology and the results show that energy efficiency and power consumption are </p><p>much better implemented and life time increases with the use of Slotted PSM.</p>

<p>Exploitation of wireless sensor networks (WSNs) in ubiquitous computing environments is continuously increasing for gathering data. Contemporary distributed software systems on WSNs for pragmatic business applications have become extremely adaptive, dynamic, heterogeneous and large scaled. Management of such system is not trivial to fulfil these features, leading to more and more complex management and configuration. Along with encompassing state of art and novel techniques for such diversely dynamic system, in this thesis two alternative techniques namely “task initiation by command” and “run-time task deployment and processing” are compared, for such system’s setup and configuration. Both techniques have their own pros and cons which makes them suitable according to the requirements and contextual situations. A lot of effort has been put to make WSNs more and more efficient in terms of computations and power consumption. Hence comparative analysis of both techniques used in this report to setup and configure WSN can be a benchmark to lead towards most appropriate solution to compensate the need of efficient energy and resource consumption.Both alternative schemes are implemented to setup WSN on Sun Microsystems sunSPOT (Small Programmable Object Technology) sensor nodes which are embedded microcontrollers and programmed them in java (j2me). It performs radio communication between wireless sensors and host via sink node also called base station, along with over the air run-time management of sensors. SunSPOTs built in libraries and KSN libraries are used to implement these alternatives and compare the memory footprint, communication pattern and energy consumption.Exploitation of wireless sensor networks (WSNs) in ubiquitous computing environments is continuously increasing for gathering data. Contemporary distributed software systems on WSNs for pragmatic business applications have become extremely adaptive, dynamic, heterogeneous and large scaled. Management of such system is not trivial to fulfil these features, leading to more and more complex management and configuration. Along with encompassing state of art and novel techniques for such diversely dynamic system, in this thesis two alternative techniques namely “task initiation by command” and “run-time task deployment and processing” are compared, for such system’s setup and configuration. Both techniques have their own pros and cons which makes them suitable according to the requirements and contextual situations. A lot of effort has been put to make WSNs more and more efficient in terms of computations and power consumption. Hence comparative analysis of both techniques used in this report to setup and configure WSN can be a benchmark to lead towards most appropriate solution to compensate the need of efficient energy and resource consumption.Both alternative schemes are implemented to setup WSN on Sun Microsystems sunSPOT (Small Programmable Object Technology) sensor nodes which are embedded microcontrollers and programmed them in java (j2me). It performs radio communication between wireless sensors and host via sink node also called base station, along with over the air run-time management of sensors. SunSPOTs built in libraries and KSN libraries are used to implement these alternatives and compare the memory footprint, communication pattern and energy consumption.</p>