The meteoric rise and prevalent usage of wireless networking technologies for mobile communication applications have captured the attention of media and imagination of public in the recent decade. One such proliferation is experienced in Wireless Sensor Networks (WSNs), where multimedia enabled elements are fused with integrated sensors to empower tightly coupled interaction with the physical world. As a promising alternative to antiquated wired systems and traditional WSNs in a multitude of novel application scenarios, the newly renovated WSNs have inspired a wide range of research among which investigation on data acquisition techniques is a fundamental one. In this dissertation, we address the problem of data acquisition in next generation WSNs. As wireless sensors are powered with limited energy resources while they are expected to work in an unattended manner for a long duration, energy conservation stands as the primal concern. Also, to enable in-situ sensing in different rate-constrained applications, routing decisions should care about the medium access feasibility of achievable end-to-end data rates. Driven by the fact, we first design cross-layer medium contention aware routing schemes for rate-constrained traffic in single-channel WSNs that maximize network lifetime. Three sufficient conditions on rate feasibility, referred to as rate-based, degree-based, and mixed constraints, are incorporated into the routing formulations to guarantee the practical viability of the routing solutions. Next, with the aim to mitigate interference and hence to enhance network capacity, we extend our work by proposing energy and cross-layer aware routing schemes for multichannel access WSNs that account for radio, MAC contention, and network constraints. In that context, we first derive three new sets of sufficient conditions that ensure feasibility of data rates in multichannel access WSNs. Then, utilizing these sets, we devise three different MAC-aware routing optimization schemes, each aiming to maximize the network lifetime while meeting data rate requirements of end-to-end flows. Finally, we perform extensive simulation studies to evaluate and compare the performance of the proposed routing approaches under various network conditions. So far works are done in milieu of WSNs with both fixed access node and sensor nodes. In the subsequent part of the dissertation, we present the continuation of our work focusing on reliable data acquisition in Mobile WSNs for a promising application namely free-ranging animal tracking/monitoring. To accomplish that goal, we concentrate on providing sufficient conditions on access-point density that limit the likelihood of buffer overflow. We first derive sufficient access-point density conditions that ensure that the data loss rates are statistically guaranteed to remain below a given threshold. Then, we evaluate and validate the derived theoretical results with both synthetic and real-world data. / Graduation date: 2012

Many applications of wireless sensor networks (WSNs) require the sensor nodes of a network to belong to different priority classes where the nodes of a higher priority class enjoy higher data rates than nodes of a lower priority class. Practical design of such networks, however, faces challenges in satisfying the following basic design requirements: a) the need to rely on the medium access control mechanisms provided by the IEEE 802.15.4 standard for low-rate wireless personal area networks, b) the need to solve certain types of class size optimization problems to ensure adequate sensing coverage, and c) the need to achieve good utilization of the available channels. Unfortunately, the current version of the IEEE 802.15.4 does not provide adequate support for rate differentiation. Hence, many proposed solutions to the problem in the literature consider adding extensions to the standard. In this thesis, we introduce some class size optimization problems as examples of coverage problems that may arise in designing a WSN. We then consider a method proposed in the literature for handling the rate differentiation problem. The method relies on modifying the CSMA-CA channel access mechanism of the IEEE standard. We use simulation to examine its performance and its applicability to solve some class size optimization problems. We next investigate the use of Time Division Multiple Access (TDMA) protocols in providing service differentiation among different classes of sensors. We show simple sufficient conditions for the existence of TDMA-based solutions to a class size feasibility problem. Lastly, we consider the use of Guaranteed Time Slots (GTS) of the IEEE 802.15.4 standard in constructing TDMA schedules. We present a new algorithm that uses the GTS service to construct such schedules. The desired algorithm contains some optimization features. The obtained simulation results show the performance gain achieved by the algorithm.

Two new stepped-frequency continuous wave (SFCW) radar sensor prototypes, based on a coherent super-heterodyne scheme, have been developed using Microwave Integrated Circuits (MICs) and Monolithic Millimeter-Wave Integrated Circuits (MMICs) for various surface and subsurface applications, such as profiling the surface and subsurface of pavements, detecting and localizing small buried Anti-Personnel (AP) mines and measuring the liquid level in a tank. These sensors meet the critical requirements for subsurface and surface measurements including small size, light weight, good accuracy, fine resolution and deep penetration. In addition, two novel wideband microstrip quasi-TEM horn antennae that are capable of integration with a seamless connection have also been designed. Finally, a simple signal processing algorithm, aimed to acquire the in-phase (I) and quadrature (Q) components and to compensate for the I/Q errors, was developed using LabView. The first of the two prototype sensors, named as the microwave SFCW radar sensor operating from 0.6-5.6-GHz, is primarily utilized for assessing the subsurface of pavements. The measured thicknesses of the asphalt and base layers of a pavement sample were very much in agreement with the actual data with less than 0.1-inch error. The measured results on the actual roads showed that the sensor accurately detects the 5-inch asphalt layer of the pavement with a minimal error of 0.25 inches. This sensor represents the first SFCW radar sensor operating from 0.6-5.6-GHz. The other sensor, named as the millimeter-wave SFCW radar sensor, operates in the 29.72-35.7-GHz range. Measurements were performed to verify its feasibility as a surface and sub-surface sensor. The measurement results showed that the sensor has a lateral resolution of 1 inch and a good accuracy in the vertical direction with less than  0.04-inch error. The sensor successfully detected and located AP mines of small sizes buried under the surface of sand with less than 0.75 and 0.08 inches of error in the lateral and vertical directions, respectively. In addition, it also verified that the vertical resolution is not greater than 0.75 inches. This sensor is claimed as the first Ka-band millimeter-wave SFCW radar sensor ever developed for surface and subsurface sensing applications.

A distributed sensor using an optical fiber for detecting and locating intruders over long perimeters (>10 km) is described. Phase changes resulting from either the pressure of the intruder on the ground immediately above the buried fiber or from seismic disturbances in the vicinity are sensed by a phase-sensitive optical time-domain reflectometer (φ−OTDR). Light pulses from a cw laser operating in a single longitudinal mode and with low (MHz/min range) frequency drift are injected into one end of the single mode fiber, and the backscattered light is monitored with a photodetector. In laboratory tests with 12 km of fiber on reels, the effects of localized phase perturbations induced by a piezoelectric fiber stretcher on φ−OTDR traces were characterized. In field tests in which the sensing element is a single mode fiber in a 3-mm diameter cable buried in an 8 to 18 inch deep, 4 inch wide trench in clay soil, detection of intruders on foot up to 15 ft from the cable line was achieved. In desert terrain field tests in which the sensing fiber is in a 4.5-mm diameter cable buried in a 1 ft deep, 2.5 ft wide trench filled with loose sand, high sensitivity and consistent detection of intruders on foot and of vehicles traveling down a road near the cable line was realized over a cable length of 8.5 km and a total fiber path of 19 km in real time. In a final series of field tests in clay soil, phase changes produced by the steps of a person walking up to 15 ft away from the buried cable were observed, and vehicles traveling at 10 mph were consistently detected up to 300 ft away. Based on these results, this technology may be regarded as a candidate for providing low-cost perimeter security for nuclear power plants, electrical power distribution centers, storage facilities for fuel and volatile chemicals, communication hubs, airports, government offices, military bases, embassies, and national borders.

The coverage and energy issues are the fundamental problems which prevent the development of wireless sensor networks. In order to accurately evaluate the monitoring quality (coverage), one needs to model the interactive of sensors, phenomenons and the environment. Furthermore, in collaborative with scheduling algorithm and computer optimization, protocols can improve the overall monitoring quality and prolong the lifetime of network. This thesis is an investigation of coverage problem and its relative applications in the wireless sensor networks. We first discuss the realistic of current boolean sensing model and propose an irregular sensing model used to determine the coverage in the area with obstacles. We then investigate a joint problem of maintaining the monitoring quality and extending the lifetime of network by using scheduling schemes. Since the scheduling problem is NP hard, genetic algorithm and Markov decision process are used to determine an achievable optimal result for the joint problem of coverage-preserving and lifetime-prolong. In order to avoid the cost of centralized or distributed scheduling algorithms, a localized coverage-preserving scheduling algorithm is proposed by exploring the construction process of Voronoi diagram. Besides exploring the coverage characteristic in a static wireless sensor network, we investigate the coverage problem when the mobile elements are introduced into network. We consider the single-hop mobile data gathering problem with the energy efficiency and data freshness concerns in a wireless sensor network where the connectivity cannot be maintained. We first investigate the upper/lower bound of the covering time for a single collector to cover the monitoring area. Through our investigation we show that for a bounded rectangle area a hexagon walk could explore the area more efficiently than a random walk when the edges of area are known. We then propose a virtual force mobile model (VFM) in which the energy consumption for data transmission is modeled as a virtual elastic force and used to guide of mobile collectors to move to optimal positions for energy saving.

The use of carbon nanotubes (CNTs) as a material for construction of sensors is a promising effort. This is due to some unique characteristics of CNTs. In recent years, strain sensors built from CNT composite films have been developed. This thesis study first proposed that the piezoresistive sensitivity of CNT composite films can be limited due to the presence of one of the constituent elements in the CNT composite films, that is, surfactant. CNT films free of surfactants were thus hypothesized to have a great promise to improve piezoresistive sensitivity. The motivation of this thesis study was to explore this promise.<p> This thesis presents an experimental study on Single-Wall CNT (SWNT) films free of surfactants. Such SWNT films are called pure SWNT films. The study has concluded: (1) the gauge factor of one layer SWNT film is much higher than that of CNT composite film; (2) the fabrication of multilayered pure CNT films is highly possible; (3) the gauge factor of multilayered pure SWNT films (10 layers and 0.8mg/ml concentration) can reach as high as 2.59 with non-linearity of 0.89% and repeatability of 0.1%, which outperforms the strain sensor built from CNT composite films; (4) the role of surfactants is indeed restrictive to piezoresistive response, and (5) the junction theory is likely applicable to pure SWNT film sensors.<p> The main contributions of this thesis study are: (1) the finding of a new type of strain sensors built from pure CNT films and (2) the development of a fabrication process for multilayered pure SWNT films.

The use of carbon nanotubes (CNTs) as a material for construction of sensors is a promising effort. This is due to some unique characteristics of CNTs. In recent years, strain sensors built from CNT composite films have been developed. This thesis study first proposed that the piezoresistive sensitivity of CNT composite films can be limited due to the presence of one of the constituent elements in the CNT composite films, that is, surfactant. CNT films free of surfactants were thus hypothesized to have a great promise to improve piezoresistive sensitivity. The motivation of this thesis study was to explore this promise.<p> This thesis presents an experimental study on Single-Wall CNT (SWNT) films free of surfactants. Such SWNT films are called pure SWNT films. The study has concluded: (1) the gauge factor of one layer SWNT film is much higher than that of CNT composite film; (2) the fabrication of multilayered pure CNT films is highly possible; (3) the gauge factor of multilayered pure SWNT films (10 layers and 0.8mg/ml concentration) can reach as high as 2.59 with non-linearity of 0.89% and repeatability of 0.1%, which outperforms the strain sensor built from CNT composite films; (4) the role of surfactants is indeed restrictive to piezoresistive response, and (5) the junction theory is likely applicable to pure SWNT film sensors.<p> The main contributions of this thesis study are: (1) the finding of a new type of strain sensors built from pure CNT films and (2) the development of a fabrication process for multilayered pure SWNT films.

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Denna rapport presenterar en metod som möjliggör bestämning av bredbandiga signalers infallsvinklar. Studien är gjord i Matlab där infallande signaler samplades med ett antal sensorer utplacerade ekvidistant på en rätlinje. Den samplade informationen viktades sedan med konstanter framtagna med en konvex optimeringsrutin för att bilda en vinkelberoende utsignal. Rutinerna testades för insignaler med ett få antal frekvenser och gav för alla testade insgnaler en mycket bra bestämmning av infallsvinklen. Studien visar även att det är möjligt att göra systemet mer robust mot störningar i sensorernas positioner genom att ställa kriterier på den konvexa optimerings rutinen.

Recent years have seen a tremendous growth in the development of small sensing devices capable of data processing and wireless communication through their embed- ded processors and radios. Wireless Sensor Networks (WSNs) are ad hoc networks consisting of such devices gaining importance due to their emerging applications. For a meaningful processing of the information sensed by WSN nodes, the clocks of these individual nodes need to be matched through some well de¯ned procedures. This dissertation focuses on deriving e±cient estimators for the clock parameters of the network nodes for synchronization with the reference node and the estimators variance thresholds are obtained to lower bound the maximum achievable performance. For any general time synchronization protocol involving a two way message ex- change mechanism, the BLUE-OS and the MVUE of the clock o®set between them is derived assuming both symmetric and asymmetric exponential network delays. Next, with the inclusion of clock skew in the model, the joint MLE of clock o®set and skew under both the Gaussian and the exponential delay model and the corresponding al- gorithms for ¯nding these estimates are presented. Also, for applications where even clock skew correction cannot maintain long-term clock synchronization, a closed-form expression for the joint MLE for a quadratic model is obtained. Although the derived MLEs are not computationally very complex, two compu- tationally e±cient algorithms have been proposed to estimate the clock o®set and skew regardless of the distribution of the delays. Afterwards, extending the idea of having inactive nodes in a WSN overhear the two-way timing message communication between two active (master and slave) nodes, the MLE, the BLUE-OS, the MVUE and the MMSE estimators for the clock o®sets of the inactive nodes located within the communication range of the active nodes are derived, hence synchronizing with the reference node at a reduced cost. Finally, focusing on the the one-way timing exchange mechanism, the joint MLE for clock phase o®set and skew under exponential noise model and the Gibbs Sampler for a receiver-receiver protocol is formulated and found via a direct algorithm. Lower and upper bounds for the MSE of JMLE and Gibbs Sampler are introduced in terms of the MSEs of the MVUE and the conventional BLUE, respectively.