The volume reduction in power converters over the past several decades can chiefly be attributed to increases in switching frequency. It is to be expected that the trends towards miniaturization will maintain steady pressure to keep this pace of increasing switching frequencies of power converters. However certain fundamental limits in high frequency power conversion are being reached as frequencies are being pushed deeper into the megahertz range, inhibiting substantial further increases. The work reported in this dissertation is intended to systematically investigate the fundamental frequency limitations, identify some of the solutions for HF/VHF power conversion and to provide guidelines and tools to optimize the performance of power converters by maximizing frequency. A number of multi-megahertz power converters are examined to evaluate the present status and future trend of HF/VHF power conversion. An interesting trend between power level and frequency is observed. A general limitation about the power level and frequency, independent of design details, is derived from the physics of the semiconductor devices, which determines the upper bound of the power levels as frequency increases. A 250 MHz DC-DC power converter (derived from the Class E power amplifier) is analyzed and demonstrated with discrete components, which again verifies the trend between power level and frequency. The power losses in the semiconductor devices are discussed, and optimization criteria for minimizing the power losses of the devices, are discussed. By relating the power losses to the semiconductor materials' properties, a methodology for selecting proper materials is identified for high frequency and high efficiency power conversion. The frequency scaling effects of passive components, still dominating the volume of the modern power converter, is analyzed. A generic multi-disciplinary methodology is developed to analyze and maximize frequency and performance of passive components in terms of power density and efficiency. It is demonstrated how the optimum frequency can be identified, and how power conversion efficiency deteriorates beyond this optimum under a fixed maximum temperature. Power loss measurement is becoming more challenging as higher frequency and higher efficiency power conversion. To achieve an accurate power loss measurement in a high frequency, high efficiency power electronics system or component, limitations of electrical measurement are identified, and various calorimetric methods are surveyed. Calorimetric methods are more accurate due to the direct heat loss measurement. An advanced calorimetric system is proposed, analyzed, and tested, demonstrating about 5% error in total losses up to 25W. / Ph. D.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / One approach to improving spectrum usage efficiency is to manage the scheduling of frequencies more effectively. The use of metrics to analyze frequency scheduling could aid frequency managers in a variety of ways. However, the basic question of what is a good metric for representing and analyzing spectral usage remains unanswered. Some metrics capture spectral occupancy. This paper introduces metrics that change the focus from occupancy to availability. Just because spectrum is not in use does not mean it is available for use. A significant factor in creating unused but unusable spectrum is fragmentation. A mission profile for spectrum usage can be considered a rectangle in a standard time versus frequency grid. Even intelligent placement of these rectangles (i.e., the scheduling of a missions spectrum usage) can not always utilize all portions of the spectrum. The average typical mission availability (ATMA) metric provides a way of numerically answering the question: Could we have scheduled another typical mission? This is a much more practical question than: Did we occupy the entire spectrum? If another mission couldn’t have been scheduled, then the entire spectrum was effectively used, even if the entire spectrum wasn’t occupied.

The demand for larger user traffic capacity and better service quality for wireless communications has been increasing drastically in the past decade due to the widespread use of internet and smart phones. However, such demand is severely limited by the shortage of radio spectrum. One of the key enabling techniques to enhance spectrum utilization efficiency is spectrum sharing, which allows unlicensed secondary users to access the spectrum of a licensed primary network under interference constraints. Traditional spectrum sharing strategies developed for finite and deterministic networks require accurate information on user locations or channel gains. It is trivial that acquiring such information consumes substantial resources in large-scale and randomly deployed wireless networks. In this thesis, innovative spectrum sharing techniques for large-scale and random geometric wireless networks are explored by utilizing stochastic geometry models. Our study covers situations where each node of both primary and secondary networks is equipped with one or more than one antenna. We also consider the scenario when multiple secondary networks are present in the communication system. / We first review the various important aspects of spectrum sharing between one primary network and one secondary network where each node is equipped with only one single antenna. We analyze the successful transmission probability of each network in this case, and derive the corresponding optimal transmit power for the secondary network. The main technical challenge is to manage intra-network and inter-network interference caused by the stochastic nature of channel propagation and node distribution. Given a decrement limit for the successful transmission probability of each network, the optimal transmit power of the secondary network is determined to boost the spectrum sharing throughput while preventing individual networks from experiencing severe performance degradation. / Secondly, two multiple-input single-output networks are investigated to further improve the performance of spectrum sharing. Multiple transmit antennas manage aggregate interference by strengthening the desired signal and nulling undesired interferers, as far as possible. Partial zero-forcing beamforming is applied to spectrum sharing networks to quantify the possible density increase in the secondary users while meeting the outage requirements of other spectrum sharing users. Furthermore, we analyze the effects of the nulled interferers, and show how spectrum sharing opportunities can be enhanced in large-scale and random geometric wireless networks by wisely allocating the degrees of freedom for interference nulling. / Lastly, motivated by the evolution of wireless networks toward heterogeneity, we study spectrum sharing between one primary network and multiple secondary networks that are distinguished by system parameters, such as network densities and target data rates. A power allocation strategy is developed for the secondary networks to improve the overall spectrum sharing throughput while guaranteeing the quality-of-service of each network. The joint power allocation problem is transformed into a power ratio allocation strategy, and a quasi-closed form solution that allows for water-filling interpretation is obtained. / 由於互网和智能手機的廣泛應用，對於無線通信中更大的用戶傳輸容量以及更好的服務質量的需求在過去十年得到了長足的增長。但是，這些需求嚴重受限于無線頻譜的不足。作為提升頻譜利用率的主要技術之一，頻譜共享允許無執照的次級用戶在干擾受限的條件下使用屬於有執照的主用戶的頻譜。傳統的頻譜共享策略針對于有限的、確定性的網絡，需要準確的用戶位置信息或信道增益信息。在大規模隨機分佈的無線網絡中，獲取這些信息會消耗大量的資源。本論文利用隨機幾何模型對於大規模隨機幾何無線網絡中的頻譜共享新技術進行了探索。我們的研究涵蓋主用戶和次用戶網絡的每個節點配置單天線和多天線的多種情況。我們還考慮了系統中有多個次用戶的情況。 / 我們首先考慮的是一個主要網絡和一個次級網絡之間的頻譜共享問題，其中每個節點配置單天線。我們分析了這個場景中每個網絡的成功傳輸概率，並提出了最優化的次級用戶傳輸功率。主要的技術挑戰是管理由於信道傳播和節點分佈的隨機性而造成的網絡內部和網絡之間的干擾。為了提升頻普共享的吞吐量並且同時防止個體網絡的性能嚴重下降，次級用戶傳輸功率在給定每個網絡的成功傳輸概率的下降限制的情況下進行優化。 / 為了進一步提高頻譜共享的性能，我們進而研究了多輸入單輸出傳輸的雙網絡頻譜共享問題。發送端利用多個天線可以盡量增加倍號強度和削減干擾，從而管理整體的干擾。在符合用戶中斷概率的要求下，利用頻譜共享網絡中的部份迫零波束成形，我們量化了次級用戶的分佈密度增長。我們進一步分析了干擾源消去的影響，其結果顯示合理分配用於干擾消去的自由度可以增加大規模隨機幾何無線網絡中的頻譜共享機會。 / 最後，基於異構無線網絡的發展趨勢，我們考慮了一個主要網絡和多個次要網絡之間的頻譜共享問題。這些網絡的系統參數，如網絡密度和目標數據速率等，不盡相同。在保證個體網絡服務質量的前提下，為了加強頻譜共享的整體吞吐量，我們提出了多個次級網絡間的功率分配策略。我們把功率分配問題轉化為功率比例分配問題，從而得到了基於注水算法的近似解析解。 / Cai, Ran. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 143-155). / Abstracts also in Chinese. / Title from PDF title page (viewed on 09, December, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

"Submitted in partial fulfillment of the requirements for the degree of Master of Business Administration from the Naval Postgraduate School, December 2009." / Advisor(s): Dew, Nicholas ; Hudgens, Bryan. "December 2009." "MBA Professional report"--Cover. Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: RFID, Radio Frequency Identification, airborne, vessel monitoring. Includes bibliographical references (p. 103-110). Also available in print.

Thesis (M.S.)--Ohio State University, 2008. / Title from first page of PDF file. Non-Latin script record Includes bibliographical references (p. 35-36).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 140-141). Also available via the Internet.

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 73-75).

Thesis (Ph. D.)--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 84-86).

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 121-123). Also available in electronic format on the Internet.

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