This dissertation addresses the problem of distributed anomaly detection in Wireless Sensor Networks (WSN). A challenge of designing such systems is that the sensor nodes are battery powered, often have different capabilities and generally operate in dynamic environments. Programming such sensor nodes at a large scale can be a tedious job if the system is not carefully designed. Data modeling in distributed systems is important for determining the normal operation mode of the system. Being able to model the expected sensor signatures for typical operations greatly simplifies the human designer’s job by enabling the system to autonomously characterize the expected sensor data streams. This, in turn, allows the system to perform autonomous anomaly detection to recognize when unexpected sensor signals are detected. This type of distributed sensor modeling can be used in a wide variety of sensor networks, such as detecting the presence of intruders, detecting sensor failures, and so forth. The advantage of this approach is that the human designer does not have to characterize the anomalous signatures in advance. The contributions of this approach include: (1) providing a way for a WSN to autonomously model sensor data with no prior knowledge of the environment; (2) enabling a distributed system to detect anomalies in both sensor signals and temporal events online; (3) providing a way to automatically extract semantic labels from temporal sequences; (4) providing a way for WSNs to save communication power by transmitting compressed temporal sequences; (5) enabling the system to detect time-related anomalies without prior knowledge of abnormal events; and, (6) providing a novel missing data estimation method that utilizes temporal and spatial information to replace missing values. The algorithms have been designed, developed, evaluated, and validated experimentally in synthesized data, and in real-world sensor network applications.

Recently, wireless sensor network (WSN) has become a promising technology with a wide range of applications such as supply chain monitoring and environment surveillance. It is typically composed of multiple tiny devices equipped with limited sensing, computing and wireless communication capabilities. Design of such networks presents several technique challenges while dealing with various requirements and diverse constraints. Performance analysis and deployment techniquesare required to provide insight on design parameters and system behaviors. Based on network calculus, a deterministic analysis method is presented for evaluating the worst-case delay and buffer cost of sensor networks. To this end,traffic splitting and multiplexing models are proposed and their delay and buffer bounds are derived. These models can be used in combination to characterize complex traffic flowing scenarios. Furthermore, the method integrates a variable duty cycle to allow the sensor nodes to operate at low rates thus saving power. In an attempt to balance traffic load and improve resource utilization and performance,traffic splitting mechanisms are introduced for sensor networks with general topologies. To provide reliable data delivery in sensor networks, retransmission has been one of the most popular schemes. We propose an analytical method to evaluate the maximum data transmission delay and energy consumption of two types of retransmission schemes: hop-by-hop retransmission and end-to-end retransmission.In order to validate the tightness of the bounds obtained by the analysis method, the simulation results and analytical results are compared with various input traffic loads. The results show that the analytic bounds are correct and tight. Stochastic network calculus has been developed as a useful tool for Qualityof Service (QoS) analysis of wireless networks. We propose a stochastic servicecurve model for the Rayleigh fading channel and then provide formulas to derive the probabilistic delay and backlog bounds in the cases of deterministic and stochastic arrival curves. The simulation results verify that the tightness of the bounds are good. Moreover, a detailed mechanism for bandwidth estimation of random wireless channels is developed. The bandwidth is derived from the measurement of statistical backlogs based on probe packet trains. It is expressed by statistical service curves that are allowed to violate a service guarantee with a certain probability. The theoretic foundation and the detailed step-by-step procedure of the estimation method are presented. One fundamental application of WSNs is event detection in a Field of Interest(FoI), where a set of sensors are deployed to monitor any ongoing events. To satisfy a certain level of detection quality in such applications, it is desirable that events in the region can be detected by a required number of sensors. Hence, an important problem is how to conduct sensor deployment for achieving certain coverage requirements. In this thesis, a probabilistic event coverage analysis methodis proposed for evaluating the coverage performance of heterogeneous sensor networks with randomly deployed sensors and stochastic event occurrences. Moreover,we present a framework for analyzing node deployment schemes in terms of three performance metrics: coverage, lifetime, and cost. The method can be used to evaluate the benefits and trade-offs of different deployment schemes and thus provide guidelines for network designers. / <p>QC 20120906</p>

Improvements in technology result in evolution of smart devices. One of such smart devices is wireless sensor nodes, which consist of a sensing board, a battery supply and a wireless antenna to transfer data. We can collect information from the environment by deploying thousands of these tiny smart devices. These devices can also be used to monitor natural habitats or used in giant machine parts for performance evolution. Energy efficient operation is an important issue for wireless sensor network design and clustering is one of the most widely used approaches for energy efficiency. This thesis study aims to analyze the performance of clustering algorithms for wireless sensor networks. We proposed five clustering algorithms and perform experiments by using real sensor hardware over different topologies to investigate energy efficiency of the clustering algorithms.

Searching for objects in physical space is one of the most important tasks for humans. Mobile sensor networks can be great tools for the task. Transient targets refer to a class of objects which are not identifiable unless momentary sensing and signaling conditions are satisfied. The transient property is often introduced by target attributes, privacy concerns, environment constraints, and sensing limitations. Transient target localization problems are challenging because the transient property is often coupled with factors such as sensing range limits, various coverage functions, constrained mobility, signal correspondence, limited number of searchers, and a vast searching region. To tackle these challenge tasks, we gradually increase complexity of the transient target localization problem such as Single Robot Single Target (SRST), Multiple Robots Single Target (MRST), Single Robot Multiple Targets (SRMT) and Multiple Robots Multiple Targets (MRMT). We propose the expected searching time (EST) as a primary metric to assess the searching ability of a single robot and the spatiotemporal probability occupancy grid (SPOG) method that captures transient characteristics of multiple targets and tracks the spatiotemporal posterior probability distribution of the target transmissions. Besides, we introduce a team of multiple robots and develop a sensor fusion model using the signal strength ratio from the paired robots in centralized and decentralized manners. We have implemented and validated the algorithms under a hardware-driven simulation and physical experiments.

Wireless sensor network (WSN) has emerged as a promising technology thanks to the recent advances in electronics, networking, and information processing. A wide range of WSN applications have been proposed such as habitat monitoring, environmental observations and forecasting systems, health monitoring, etc. In these applications, many low power and inexpensive sensor nodes are deployed in a vast space to cooperate as a network. Although WSN is a promising technology, there is still a great deal of additional research required before it finally becomes a mature technology. This dissertation concentrates on three factors which are holding back the development of WSNs. Firstly, there is a lack of traffic analysis &amp; modeling for WSNs. Secondly, network optimization for WSNs needs more investigation. Thirdly, the development of anomaly detection techniques for WSNs remains a seldomly touched area. In the field of traffic analysis &amp; modeling for WSNs, this dissertation presents several ways of modeling different aspects relating to WSN traffic, including the modeling of sequence relations among arriving packets, the modeling of a data traffic arrival process for an event-driven WSN, and the modeling of a traffic load distribution for a symmetric dense WSN. These research results enrich the current understanding regarding the traffic dynamics within WSNs, and provide a basis for further work on network optimization and anomaly detection for WSNs. In the field of network optimization for WSNs, this dissertation presents network optimization models from which network performance bounds can be derived. This dissertation also investigates network performances constrained by the energy resources available in an indentified bottleneck zone. For a symmetric dense WSN, an optimal energy allocation scheme is proposed to minimize the energy waste due to the uneven energy drain among sensor nodes. By modeling the interrelationships among communication traffic, energy consumption and WSN performances, these presented results have efficiently integrated the knowledge on WSN traffic dynamics into the field of network optimization for WSNs. Finally, in the field of anomaly detection for WSNs, this dissertation uses two examples to demonstrate the feasibility and the ease of detecting sensor network anomalies through the analysis of network traffic. The presented results will serve as an inspiration for the research community to develop more secure and more fault-tolerant WSNs. / STC

Satisfactory results obtained from sensor networks and the ongoing development in electronics and wireless communications have led to an impressive boost in the number of applications based on WSNs. Along with the growth in popularity of WSNs, previously implemented solutions need further improvements and new challenges arise which need to be solved. One of the main concerns regarding WSNs is the existence of security threats against their routing operations. Likelihood of security attacks in a structure suffering from resource constraints makes it an important task to choose proper security mechanisms for the routing decisions in various types of WSN applications. The main purpose of this study is to survey WSNs, routing protocols, security attacks against routing layer of a WSN, introduction of Trust based models which are an effective defense mechanism against security attacks in WSNs and finally, to implement a proposed Trust based routing protocol in order to overcome security attacks. The study begins with a survey of Sensor Networks, after the introduction of WSNs and their related routing protocols, the issue of security attacks against the network layer of a Sensor Network is described with a presentation of different types of attacks and some of Trust based related works. In the final chapters of this research, a novel Trust based AODV protocol will be proposed, implemented and examined in a simulation environment. For this purpose, multiple number of scenarios will be simulated on the AODV protocol with and without Trust mechanism, then the achieved results will be compared to derive a conclusion.

Satisfactory results obtained from sensor networks and the ongoing development in electronics and wireless communications have led to an impressive boost in the number of applications based on WSNs. Along with the growth in popularity of WSNs, previously implemented solutions need further improvements and new challenges arise which need to be solved. One of the main concerns regarding WSNs is the existence of security threats against their routing operations. Likelihood of security attacks in a structure suffering from resource constraints makes it an important task to choose proper security mechanisms for the routing decisions in various types of WSN applications. The main purpose of this study is to survey WSNs, routing protocols, security attacks against routing layer of a WSN, introduction of Trust based models which are an effective defense mechanism against security attacks in WSNs and finally, to implement a proposed Trust based routing protocol in order to overcome security attacks. The study begins with a survey of Sensor Networks, after the introduction of WSNs and their related routing protocols, the issue of security attacks against the network layer of a Sensor Network is described with a presentation of different types of attacks and some of Trust based related works. In the final chapters of this research, a novel Trust based AODV protocol will be proposed, implemented and examined in a simulation environment. For this purpose, multiple number of scenarios will be simulated on the AODV protocol with and without Trust mechanism, then the achieved results will be compared to derive a conclusion.

In traditional Wireless Sensor network's (WSN's), the sink is the only unconditionally trusted authority. If the sink is not connected to the nodes for a period of time then the network is considered as unattended. In Unattended Wireless Sensor Network (UWSN), a trusted mobile sink visits each node periodically to collect data. This network differs from the traditional multi hop wireless sensor networks where the nodes close to the sink deplete their power earlier than the other nodes. An UWSN can prolong the life time of the network by saving the battery of the nodes and also it can be deployed in environments where it is not practical for the sink to be online all the time. Saving data in the memory of the nodes for a long time causes security problems due to the lack of tamper-resistant hardware. Data collected by the nodes has to be secured until the next visit of the sink. Securing the data from an adversary in UWSN is a challenging task. We present two non-cryptographic algorithms (DS-PADV and DS-RADV) to ensure data survivability in mobile UWSN. The DS-PADV protects against proactive adversary which compromises nodes before identifying its target. DS-RADV makes the network secure against reactive adversary which compromises nodes after identifying the target. We also propose a data authentication scheme against a mobile adversary trying to modify the data. The proposed data authentication scheme uses inexpensive cryptographic primitives and few message exchanges. The proposed solutions are analyzed both mathematically and using simulations proving that the proposed solutions are better than the previous ones in terms of security and communication overhead.

In distributed systems, dependency among different computations of an application leads to a problem of deciding the locations of computations. Spatial requirements of a computation can be expressed in terms of spatial relationships with other computations. This research presents programming abstractions and language constructs which can be used for specifying spatial coordination requirements for distributed computations. A spatial coordination middleware has been implemented for satisfying spatial coordination requirements of systems implemented using the Actor model of concurrent computation. Our approach abstracts spatial requirements of concurrent computations and provides key programming primitives for specifying these requirements. We have also implemented a number of higher level spatial coordination primitives which can be translated into the basic primitives. Spatial requirements can be specified using these primitives and then the runtime system converts them into a constraint satisfaction problem and satisfies them. Our approach reduces the programming complexity and provides a middleware which separates spatial requirements from functional code and enables the application programmer to change spatial requirements at runtime without effecting application's functionality. We have identified some of the high level primitives and provided a mechanism to develop high level primitives on top of the basic primitives. This thesis presents the rationale, design, implementation, and evaluation of spatial coordination. By comparing programs written with and without our spatial coordination primitives, we show how spatial coordination enables a programmer to specify spatial requirements declaratively and simplify the programming task. Experimental results demonstrate the performance of the approach, as the number of constraints increases.

Coverage in a Wireless Sensor Network reflects how well a sensor network monitors an area. Many times it is impossible to provide full coverage. The key challenges are to prolong the lifetime and ensure connectivity to provide a stable network. In this thesis we first define p-percent coverage problem in which we require only p% of the whole area to be monitored. We propose two algorithms, Connected P-Percent Coverage Depth First Search (CpPCA-DFS) and Connected P-Percent Connected Dominating Set (CpPCA-CDS). Through simulations we then compare and analyze them for their efficiency and lifetime. Finally in conclusion we prove that CpPCA-CDS provides 5 to 20 percent better active node ratio at low density. At high node density it achieves better distribution of covered area however the lifetime is only 5 to10 percent shorter then CpPCA-DFS. Overall CpPCA-CDS provides up to 30 percent better distribution of covered area.