This document describes the theory, design and implementation of a digital receiver designed for the ACTS propagation experiments. The Virginia Tech Satellite Communications Group is designing, constructing and distributing eight ACTS propagation terminals (APTs) under a contract with NASA. The terminals will measure the received signal power from the ACTS satellite beacons (20 GHz, 27.5 GHz) in various climates at different elevation angles. The resulting signal power measurement, radiometer and weather measurement data will be used to characterize atmospheric effects on signal propagation at Ka band. Each APT system will contain two identical, independent digital receivers; one 20 GHz channel and one 27.5 GHz channel. The algorithm implemented on each receiver utilizes the results of multiple fast Fourier transforms to reliably identify the carrier tone amidst neighboring modulation tones. The acquisition procedure, can reliably identify the carrier signal at signal-to-noise ratios down to 10 dB in a 20 Hz bandwidth (23 dBHz in a 1 Hz bandwidth, -26 dB relative to clear air conditions on the APT system) in 2 seconds. The receiver then uses a comb filter, two FIR filters and additional FFTs to produce power measurements accurate to 0.1 dB at signal-to-noise ratios down to 5 dB in a 20 Hz bandwidth (18 dBHz in a 1 Hz bandwidth, -31 dB relative to clear air conditions on the APT system) at 1 Hz and 20 Hz sampling rates. The algorithm also provides several supplemental functions including a software selectable detection bandwidth from 2 Hz to 50 Hz (1 Hz increments), spectrum analyzer type output for a 303.333 kHz bandwidth centered on the current carrier frequency and carrier frequency estimates accurate to ±O. 5 Hz. / Master of Science

An extensive radio wave propagation measurement campaign was conducted at 1.3 GHz and 4.0 GHz inside four buildings, including a sports arena, a modern closed-plan office building, and two dissimilar, open-plan factories. Measurements were recorded at 57 locations using base station antenna heights of 1.7 meters and 4.0 meters. Results were obtained for mean and maximum excess delay, rms delay spread, time delay jitter, differential delay jitter, and path loss through analyses of impulse response estimates, which were obtained via repetitive 5 ns probing pulses. The effects of frequency, antenna height, topography (line-of-sight or obstructed direct path), and building environment on delay spread and path loss are quantified. Results indicate that, on average, the frequencies and antenna heights used in this study have minimal impact on rms delay spread and path loss. However, topography and building environment significantly affect these parameters. RMS delay spread values as high as 230 ns were observed in open plan factories. Computed path loss power law exponents are 1.84 and 2.35 for line-of-sight and obstructed topographies, respectively. A second campaign was conducted to determine the effects of antenna directivity and polarization on propagation parameters. On average, line-of-sight indoor channels offer 8 dB of cross-polarization discrimination, whereas obstructed environments offer less than 3 dB. Directional antennas provide a significant reduction in rms delay spread over omni-directional antennas. In line-of-sight environments, circular polarization provides an additional delay spread reduction. / Master of Science

The radio interface greatly affects performance of wireless communication systems. Hard-wired communication links use transmission lines to connect communication terminals. The propagation characteristics of radio frequency signals on these transmission lines are well known. In wireless communication systems, however, the transmission line with a known impulse response is replaced by a radio channel with an impulse response that is constantly changing as the users roam throughout the coverage area. The varying impulse response is due to the multiple path propagation of the signals from the transmitter to the receiver. The design of emerging small cellular (commonly known as microcellular) wireless systems is limited by the multipath propagation characteristics of the channel. Once these propagation conditions are understood, systems may be designed more efficiently in terms of cell layout, interference reduction, and system performance. This thesis presents a technique for automated propagation prediction in outdoor microcellular radio channels using ray tracing. The basic method is to integrate site-specific environmental data with a geometrical optics model to trace the propagation of energy from the transmitter to the receiver. Software written in C++ is used to automatically trace rays that are reflected, transmitted, scattered, or diffracted as they propagate through the channel. The automated software uses AutoCAD® to maintain the site-specific building data incorporated into the model. Details of the building database, propagation model, and software implementation are included in this thesis. The accuracy of the model and its software implementation is tested against wide band measurements taken on the Virginia Tech campus. Results, included here, indicate that the received signal can be accurately predicted in both line-of-sight and obstructed microcell topographies. / Master of Science

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Low power, high speed serial transceivers are employed in a wide range of applications ranging from chip-to-chip, backplane, and optical interconnects. Apart from being capable of handling a wide range of data rates, the transceivers should have low power consumption (mW/Gbps) and be fully integrated. This work discusses enabling techniques to implement such transceivers. Specifically, three designs: (1) a 0.5-4 Gbps serial link which uses current recycling to reduce power dissipation and (2) a 0.5-2.5 Gbps reference-less clock and data recovery circuit which uses a novel frequency detector to achieve unlimited acquisition range and (3) a 2-4 Gbps low power receiver architecture capable of resolving multiple signalling formats with a simplified XOR based phase rotating PLL will be presented. All the three circuit topologies are highly digital and aim to address the requirements of wide operating range, low power dissipation while being fully integrated. Measured results obtained from the prototypes illustrate the effectiveness of the proposed design techniques. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Dec. 2, 2011 - June 2, 2012

The objective of the proposed research is to develop simplified reconfigurable transmission systems with frequency multipliers for the transmission of complex modulated signals. Because they rely on nonlinear properties, frequency multiplier-based transmission systems require proper linearization techniques and accurate modeling of the signal transfer function. To accomplish these two goals, the author has developed techniques to model and linearize frequency multipliers and to digitize feedback signals for nonlinear characterization. First, adaptive predistortion techniques and zonal transfer theories have been developed for modeling and linearization. The predistortion system has been verified by applying an IS-95B signal to various frequency multipliers built by the author. Second, because the output signals at higher harmonic zones occupy wider frequency bandwidths than the signal in the fundamental zone does and thus make it harder to use traditional sampling techniques, a simplified but effective method called the sub-Nyquist sampling rate was developed and verified. Third, two methods for reconfigurable transmitters using frequency multipliers in conjunction with digital predistortion linearizers were developed. Both methods make it possible to transmit complex signals via frequency multipliers by using dual-band transmission systems that incorporate frequency multipliers that are based on linearization techniques. One of these methods uses a circuit topology that can be switched between a fundamental-mode in-phase combined amplifier and a push-push frequency doubler using input phasing. The second suggested method uses a fundamental-frequency power amplifier followed by a varactor multiplier that can be bypassed with an RF switch. This work will contribute to the development of low-cost and size-effective reconfigurable transmission systems because it requires fewer transmitting components and needs less sampling of the feedback networks.

Les Réseaux de Capteurs Sans Fils (RCSFs) sont composés d'une multitude de nœuds, chacun étant capable de réaliser des mesures (température, pression, etc) et de communiquer par radio fréquence. Ces réseaux forment une pierre angulaire de l'Internet des Objets, en étant au cœur de nombreuses applications, par exemple de domotique ou d'agriculture de précision. La limite d'utilisation des RCSFs provient souvent de leurs durées de vie restreintes, les rendant peu intéressants pour des applications nécessitants de longues périodes de fonctionnement en autonomie. En effet, les RCSFs traditionnels sont alimentés par des piles individuelles équipant chaque nœud, et les nœuds sont ainsi condamnés à une durée de vie finie et courte par rapport aux besoins de certaines applications. De plus, changer les piles n'est pas toujours réalisable si le réseau est dense, ou si les nœuds sont déployés dans des environnements les rendant difficile d'accès. Une solution plus prometteuse est d'équiper chaque nœud d'un ou de plusieurs récupérateur(s) d'énergie individuel(s), et ainsi de le rendre capable de s'alimenter exclusivement à partir de l'énergie récoltée dans son environnent. Plusieurs sources d'énergie sont possibles, telles que le vent ou le solaire. Étant donné que les sources d'énergie sont typiquement dynamiques et non contrôlées, ne pas tomber en panne d'alimentation et nécessaire pour garantir un fonctionnement fiable. Comme l'augmentation de la qualité de service engendre souvent une augmentation de la puissance consommée, une solution simple est de configurer la qualité de service au déploiement à une valeur constante suffisamment faible pour éviter la panne d'alimentation. Cependant, cette solution ne permet pas d'exploiter pleinement l'énergie récoltée, et mène ainsi à un gaspillage d'énergie important ainsi qu'à de faibles qualités de service au vu de l'énergie récoltée. Une solution plus efficace est d'adapter dynamiquement la puissance consommée, et donc la qualité de service. Cette adaptation est faite par un composant logiciel appelé gestionnaire d'énergie. Dans cette thèse, deux nouvelles approches pour l'adaptation en ligne sont proposées, l'une s'appuyant sur la théorie du contrôle floue, et l'autre sur l'apprentissage par renforcement. De plus, comme la communication est souvent la tâche la plus énergivore dans les RCSFs, les wake-up receivers sont utilisées dans cette thèse pour réduire le coût des communications. Un modèle analytique générique a été proposé pour étudier différents protocoles de contrôle d'accès au support (Medium Access Control -- MAC), et combiné à des résultats expérimentaux pour évaluer les wake-up receivers. Aussi, un nouveau protocole MAC permettant la sélection opportuniste de relais a été proposé. Enfin, la combinaison des wake-up receivers et de la récolte d'énergie a été étudiée expérimentalement avec un cas pratique. / Wireless Sensor Networks (WSNs) are made of multiple sensor devices which measure physical value (e.g. temperature, pressure...) and communicate wirelessly. These networks form a key enabling technology of many Internet of Things (IoT) applications such as smart building and precision farming. The bottleneck of long-term WSN applications is typically the energy. Indeed, traditional WSNs are powered by individual batteries and a significant effort was devoted to maximizing the lifetime of these devices. However, as the batteries can only store a finite amount of energy, the network is still doomed to die, and changing the batteries is not always possible if the network is dense or if the nodes are deployed in a harsh environment. A promising solution is to enable each node to harvest energy directly in its environment, using individual energy harvesters. As most of the energy sources are dynamic and uncontrolled, avoiding power failures of the nodes is critical to enable reliable networks. Increasing the quality of service typically requires increasing the power consumption, and a simple solution is to set the quality of service of the nodes to a constant value low enough to avoid power failures. However, this solution does not fully exploits the available energy and therefore leads to high energy waste and poor quality of service regarding the available environmental energy. A more efficient solution is online adaptation of the node power consumption, which is performed by an energy manager on each node. In this thesis, two new approaches for online adaptation of the nodes energy consumption were proposed, relying on fuzzy control theory and reinforcement learning. Moreover, as communications are typically the most energy consuming task of a WSN node, emerging wake-up receivers were leveraged to reduce the energy cost of communications. A generic analytical framework for evaluating Medium Access Control (MAC) protocols was proposed, and it was combined to experiments to evaluate emerging wake-up receivers. A new opportunistic MAC protocol was also introduced for "on-the-fly" relay selection. Finally wake-up receivers and energy harvesting were combined and experimentally evaluated in a practical use case.

This study investigates whether quality management has developed to such an extent that retailers, service repair organisations and consumers are satisfied with product and repair service quality provided by South African manufacturing companies. To investigate these aspects, the colour television industry has been selected because it contains various manufacturing companies of varying sizes and characters, employing different quality policies and performances. It offers relatively standardised products and services, which facilitates intercompany comparisons and employs a simple flow type assembly line process that is representative of other mass production industries. The hypotheses are tested by interviewing four selected populations by means of carefully constructed questionnaires, namely a retail population, a repair service population, a consumer population and a manufacturing population. The empirical results are statistically evaluated in terms of the various manufacturers ability to provide satisfactory product and repair service quality. Consumers and repair service organisations are selected because they represent a broad spectrum of the population with varying, but important opinions on product and repair service quality. Retailers selling colour television receivers are also selected as they play an important role in the management of quality and vary from small independent retailers to large chain stores and discounters. The results obtained from this study show that: • there is a need from the retailers, service repair organisations and consumers for the South African manufacturers to improve the quality of colour television receivers • there is a need by the consumers and the retailers for the manufacturers to improve their repair service quality • there is a need to improve the quality control procedures employed by the colour television manufacturers. / Business Management / D. Com. (Business Management)