The objective of the proposed research is to extend the battery life in cellular handsets by improving the transmitter efficiency. Bandwidth efficient modulation formats, such as W-CDMA, encode much of the information in amplitude modulation. Therefore, linear transmitters must be used so as not to increase transmission errors, and cause interference in adjacent bands. Various engineering trade-offs were examined to find a suitable transmitter architecture for W-CDMA. Dynamic biasing of the transmitter power amplifier (PA) provides a simple way to improve efficiency for applications that require highly linear amplification. The envelope elimination and restoration (EER) PA or EER-based polar-modulated PA is an attractive solution since it has potential to achieve very high efficiency with high linearity. However, the major impediment to EER implementation has been the lack of power-efficient dynamic power supply circuits that can operate with sufficient modulation bandwidth, and simultaneously achieve the required modulation linearity. This work proposes several solutions to this problem. First, a dynamic supply circuit using delta modulation was designed and implemented. An open-loop EER PA with 48% peak efficiency was constructed and tested with a cellular band IS-95 CDMA signal with a bandwidth of 1.25 MHz. The low switching loss by using a delta modulator made the implementation of a wideband dynamic biasing circuit possible. Second, a dynamic supply circuit using dual-phase PWM was designed and implemented to achieve wider bandwidth, lower noise, and higher efficiency. An open-loop EER PA was implemented with the dynamic supply IC. A digital gain compensation scheme was developed to further increase bandwidth and linearity. This enables a dynamic supply circuit with lower switching frequency to have larger usable bandwidth with little increased power consumption. A cellular band W-CDMA voice signal was used to evaluate the performance of the overall PA. The PA achieved 50% efficiency while passing all required spectral specifications of W-CDMA standard. To increase the inherent low dynamic range of an EER PA, a dual-mode power amplifier combining an EER PA and power-level tracking PA was proposed. This work will contribute to the development of high efficiency, small-sized multi-mode linear PAs for battery-operated wireless handheld devices.

Thesis (Ph. D.)--University of Amsterdam, 1936. / Cover title.

Thesis (doctoral)--Aarhus universitet, 1993. / Summary in English. Includes bibliographical references (p. [343]-371) and index.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-01T12:55:12Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertacao Antonio Nascimento.pdf: 2311695 bytes, checksum: b542c4d4f9b8c4d8e7e4f07b723f9f93 (MD5) / Made available in DSpace on 2016-07-01T12:55:12Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertacao Antonio Nascimento.pdf: 2311695 bytes, checksum: b542c4d4f9b8c4d8e7e4f07b723f9f93 (MD5) Previous issue date: 2015-08-27 / Um diagrama EER para ser válido deve estar em conformidade com as regras sintáticas da sua linguagem de modelagem e não deve possuir construções que se contradizem estruturalmente. Considerando um diagrama EER sintaticamente correto, existem trabalhos que definem validações estruturais para os tipos básicos de relacionamentos (i.e., unários, binários e ternários), mas que não abordam construções avançadas (e.g., relacionamento identificador, herança e atributo discriminador). Neste contexto, tendo como base os trabalhos relacionados, a contribuição original desta dissertação é a definição de um catálogo de regras para validação estrutural de construções avançadas da linguagem de modelagem EER. A sistemática para definição deste catálogo consiste em realizar todas as combinações, sintaticamente válidas, entre os principais construtores da EER e avaliar quais destas têm problemas estruturais. Por fim, são propostas definições matemáticas das regras e a implementação destas em uma ferramenta do tipo Computer-Aided Software Engineering (CASE). / A EER diagram to be valid must be in accordance with the syntactic rules of their modeling language and must not have buildings that structurally contradict. Considering a syntactically correct EER diagram, there are works that define structural validations for the basic types of relationships (i.e., unary, binary and ternary), but do not address advanced buildings (e.g., identifier relationship, inheritance and discriminator attribute). In this context, based on the related works, the original contribution of this work is the definition of Catalog of Rules for Structural Validation of advanced buildings of the EER modeling language. The systematic for definition this catalog consists to realize all combinations, syntactically valid, among the main builders of EER and evaluate which of these are structural problems. Finally, the work proposes mathematical definitions of rules and implementation of these in one Computer-Aided Software Engineering (CASE) tool.

Modern communication systems operate with high peak-to-average-power ratio (PAPR) over wide bandwidth. Linearity requirements force operation in a low efficient highly linear back-off region. Then increasing efficiency is becoming critical. One of the most promising technologies to accomplish this is using supply modulation, e.g. envelope tracking (ET) and envelope elimination and restoration (EER). Supply modulated systems have been studied extensively in the past years, but no systems have been presented with flexibility in the envelope amplifier circuit.   In this work the supply modulator amplifiers have been studied. The focus is on hybrid switching amplifier (HSA) as envelope amplifier. Two envelope amplifier prototypes P-I and P-II have been designed. They are both designed for 15W output but P-II has 28V maximum supply voltage and P-I has 15V maximum supply voltage. P-II developed in version A, using silicon (Si) based switching transistor and version B using gallium-nitride (GaN) switching transistor. The efficiency is limited to a maximum 97 % possible by the circuit components.   The linearity was mainly analyzed by AM-AM diagrams. P-I, P-IIA and P-IIB, were analyzed in simulations and measurements. Results show high possibility of improvement with digital processing, i.e. digital pre-distortion (DPD). Linearization will improve the overall performance in the supply modulator (SM) systems, improving the delay issues and distortion produced by the implementation of the system.   The developed flexible board has made it possible to investigate alternative technologies of ET, focused in the hybrid switching amplifier (HSA). This has given the possibility to compare the overall performance for a traditional Si based switch with the novel Ferdinand Braun Institute’s (FBH) GaN-HEMT based switch with regards to bandwidth, efficiency and non-linearities introduced by the envelope tracking amplifier. P-I and P-II show high efficiency (> 60%) in results. For signals with adequate average power levels the efficiency is high, with around 70% efficiency for WCDMA signals. Phase distortions are evident already at a 5 MHz bandwidth.

The Psychrometric Testing Facility at the Riverside Energy Efficiency Laboratory at Texas AandM University has not been operational for several years. The goal of this project was to restore the testing facility to a fully operational condition for the purpose of supporting research and cooling capacity testing, with the latter following the appropriate standards. Numerous changes were made to the coolant piping system, the data acquisition system, instrumentation, and temperature and humidity control to update and improve the facility. In addition, a computer program was developed and implemented that allows for flexible control of the facility’s conditions and collection of data while showing real time performance and refrigerant and psychrometric calculations. The current program flexibility, along with the proper combination of instrumentation, allows the Psychrometric Facility to operate with separate steady state environmental conditions in each room, according to, and meeting, the AHRI 210/240 standard. Cooling capacity testing done on a split system residential unit was compared to the published AHRI rating to benchmark the state of the facility. Tested cooling capacity was about 3 percent below the published cooling capacity; tested EER was about 7 percent below the published EER; and finally, the calculated SEER based on the default degradation coefficient was about 10 percent below the published SEER. The difference in the calculated performance parameters to the published are expected due to unknown testing conditions used to calculate the published rating.

Intelligent Tutoring Systems (ITSs) have been shown to significantly improve students' learning in a variety of domains, including physics, mathematics, and thermodynamics. Tutorial dialogues is one of the strategies used by ITSs and has been empirically shown to significantly improve learning. This project investigates how different students interact with the tutorial dialogues in EER-Tutor, using both eye-gaze data and student-system interaction logs. EER-Tutor is a constraint-based ITS that teaches conceptual database design. In order to have a more comprehensive and accurate picture of a user's interactions with a learning environment, we need to know which interface features s/he visually inspected, what strategies s/he used and what cognitive efforts s/he made to complete tasks. Such knowledge allows intelligent systems to be proactive, rather than reactive, to users' actions. Eye-movement tracking is therefore a potential source of real-time adaptation in a learning environment. Our findings indicate that advanced students are selective of the interface areas they visually focus on whereas novices waste time by paying attention to interface areas that are inappropriate for the task at hand. Novices are also unaware that they need help with understanding the domain concepts discussed in the tutorial dialogues. We were able to accurately classify students, for example as novice or advanced students, using only eye-gaze or EER-Tutor log data as well as a combination of EER-Tutor and eye-gaze features. The cost of eye-tracking is justified as classifiers using only eye-gaze features sometimes perform as well as those utilising both EER-Tutor and eye-gaze data and outperform classifiers using only EER-Tutor data. The ability to classify students will therefore allow an ITS to intervene when needed and better guide students' learning if it detects sub-optimal behaviour.

As one of the central problems in the area of Intelligent Tutoring Systems (ITSs), student modelling has been widely used to assist in systems’ decision making and students’ learning. On the one hand, by reasoning about students’ knowledge in the instructional domain, a system is able to adapt its pedagogical actions in order to provide a customized learning environment. These actions may include individualized problem-selection, tailored instructions and feedback, as well as updating the presentation of student models. On the other hand, students can reflect on their own learning progress by viewing individual Open Student Models (OSMs) and enhance their meta-cognitive skills by learning from the system’s estimation of their knowledge levels. It is believed that making the information in the student model available to students can raise students’ awareness of their strengths and weaknesses in the corresponding domain and hence allow them to develop a more effective and efficient way of learning. An OSM has been developed in EER-Tutor. EER-Tutor is a web-enhanced ITS that supports university students in learning conceptual database modelling. Students design Enhanced Entity-Relationship (EER) diagrams and receive different level of feedback in a problem-solving environment. The pedagogical decisions on feedback generation and problem selection are made according to student models. Previously, student models in EER-Tutor are presented to students on request as skill meters. Skill meters have been proved useful in helping students to improve their meta-cognitive skills. However, as the simplest presentation of a student model, skill meters contain very limited information. Some studies show that an OSM with multiple views is more effective since it supports individual preferences and different educational purposes. The focus of our work is to develop a variety of presentations for the OSM in EER-Tutor. For this purposes, we have modified the system to include not only skill meters but also other presentation styles. An evaluation study has been performed after the development. Both subjective and objective results have been collected. This thesis presents the extended EER-Tutor, followed by the analysis of the evaluation study.

Inaug. diss.--Gothenburg University. / Extra t.p., with thesis statement, inserted. Includes bibliographical references.

Submitted by Natalia de Souza Gonçalves (natalia.goncalves@ufpe.br) on 2016-09-28T12:45:56Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Helton_10_05_16.pdf: 2471864 bytes, checksum: 84ec1446c8bac02d76bd26a6c12e8896 (MD5) / Made available in DSpace on 2016-09-28T12:45:56Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Helton_10_05_16.pdf: 2471864 bytes, checksum: 84ec1446c8bac02d76bd26a6c12e8896 (MD5) Previous issue date: 2016-02-12 / O modelo Entidade-Relacionamento Estendido (EER) e o Diagrama de Classes (DC) da Unified Modeling Language (UML) são as notações gráficas mais utilizadas para a fase de projeto conceitual de banco de dados. Neste contexto, considerando que existem diferenças entre estas notações e poucos trabalhos que as comparem a partir de uma avaliação quantitativa, este trabalho busca evidências empíricas, por meio da execução de um survey, sobre a compreensão e preferência de uso dessas notações. Como resultado, constatou-se que as duas notações cumprem os requisitos em um ambiente de desenvolvimento de banco de dados, variando sua utilização conforme o perfil do usuário. Contudo, apesar da notação do DC ser a mais compreendida, a notação EER foi a mais preferida. / The Entity-Relationship Extended (EER) model and the Class Diagram (DC) of the Unified Modeling Language (UML) are the most used graphical notations during the conceptual design phase of a database development project. In this context, considering that there are significant differences between these two notations and few studies that compare them from a quantitative approach, this paper seeks empirical evidence through the execution of a survey on the understanding and preference of use of such notations. As a result, it was found that both notations meet the requirements in a database development environment, with their use varying according to the user profile. However, despite the DC notation be better understood, the EER notation was the most preferred among the survey participants