Browsing by Subject "Communications"
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Item Capacity of multi-antenna ad hoc networks via stochastic geometry(2012-12) Hunter, Andrew Marcus; Andrews, Jeffrey G.; de Veciana, Gustavo; Heath, Robert W.; Stone, Peter; Haenggi, MartinThis thesis takes as its objective quantifying, comparing, and optimizing multiple-antenna (MIMO) physical layer techniques in dense ad hoc wireless networks. A framework is developed from the spatial shot noise interference model for packet radio network analysis. The framework captures the behavior of a wide variety of signal and interference distributions, which permit inspection of a number of signal processing methods including representatives from most of the major MIMO techniques. Multi-antenna systems for point-to-point are becoming mature and being developed and deployed in many wireless communication systems due to their potential to combat fading, increase spectral efficiency, and overcome interference. The framework permits an algorithm or system designer to view the network from the perspective of a typical user, to optimize performance in the midst of a given environment, or to view the network as a whole, to determine behavior that maximizes network performance. In particular, it enables questions to be answered quantitatively, such as which MIMO techniques perform best in a given environment? Or what rate and power settings should be used across the available spatial modes? Or what is the maximum benefit of channel state information? Or what gain should an individual device, or the network as a whole expect to see given a particular physical layer strategy? The dissertation begins by developing the framework for a generic set of assumptions on network behavior and signal and interference distributions. It then presents a progression of applications to representative MIMO techniques. Broad and intuitive scaling laws are developed as well as detailed exact results for careful comparison. Capacity scaling with the number of antennas is given for systems employing beamforming, selection combining, space-time block coding, and spatial multiplexing. These applications are used as the basis for developing simple distributed algorithms for optimizing MIMO settings with QoS constraints and in heterogeneous networks. Lastly, the framework is expanded to permit comparison and optimization of MIMO performance under alternative medium access strategies. In general it is found that significant performance gains can be reaped with multi-antenna physical layers, provided the proper techniques are employed. It is also shown that the availability of multiple spatial channels impacts the inherent tradeoff between per-link throughput and spatial reuse.Item Competencies, Importance, and Motivations for Agricultural Producers' Use of Online Communications(2013-05) Shaw, Kelsey E; Meyers, Courtney; Doerfert, David; Irlbeck, EricaFarmer demographics are drastically changing and it is essential that farmers and ranchers are taking the story of agriculture directly to the consumer. Online communication tools may serve as a tool for this farmer to consumer communication. The purpose of this study was to determine agriculturists’ use of online communication tools. The target population for this study was members of organizations targeting beginning farmers and ranchers in Texas, Illinois, and Georgia. An online survey was administered electronically to members of seven organizations, and 185 completed questionnaires were analyzed for this study. It was determined that agriculturists of all levels of experience are not currently utilizing online communication tools to their full potential, for either business or personal reasons. Additionally, several specific training needs were identified regarding these tools. A wide variety of motivations and barriers were identified that might encourage or discourage agriculturists from attending future training sessions.Item Creating a promotional DVD for an international agricultural research center: a Delphi study(Texas Tech University, 2006-08) Stockard, Stacy A.; Brashears, Michael T.; Davis, Chad S.; Brooks, Chance J.; Akers, CindyThis study used a three-round Delphi to determine what content to put in a promotional DVD for the International Center for Food Industry Excellence, an animal and food science research center. Board members and staff of the center were selected to be in the panel of experts. The first round of open-ended questions yielded 97 items. The second round used a four-point Likert scale, and panelists reached a consensus on 65 items from Round 1 they believed should be included on the DVD. Round 3 found a consensus on 3 items which previously did not reach consensus in Round 2. The study recommended the DVD focus on items that reached 100% consensus and also show items which reached at least 80% and less than 100% consensus in less depth.Item Effects of an innovative recruitment workshop on selected Texas urban high school students' knowledge and perceptions of agriculture(2009-05-15) Fraze, Lacee BrianneThe Big City, Big Country Road Show (BC2BC) is a 2.5-year project designed to recruit non-traditional populations, urban and minorities, into post-secondary agricultural science degree programs. Through experiential learning, BC2BC introduces students to various agricultural communications skill sets in an effort to broaden students? views of opportunities in agriculture. This study attempted to measure Texas urban high school students? perceptions of agriculture as a subject, a college major, and a career, before and after participation in the BC2BC program in summer of 2007. The study also looked at students? perceptions of careers attainable with an agricultural degree and students? general agricultural knowledge levels, self-reported and tested. Pre?and post?test mean comparisons revealed positive increases in student perceptions of agriculture and an increase in self-reported agricultural knowledge levels after workshop participation. The results of this study have implications for year two BC2BC workshops and may serve as a potential model for recruitment programs of underrepresented populations into colleges of agriculture.Item Examining Texas diversity : identifying the composition of diversity and the coverage of a minority-related issue in the top ten daily Texas newspapers(2015-05) Mastervich, Ashley C.; Rivas-Rodriguez, Maggie; Jensen, RobertA newsroom may be fast-paced and exhilarating; and the prestige of reporting, editing or managing for a well-known newspaper in the United States is a dream that aspiring journalists long for. The first goal of this study is to examine the existing diversity in the top ten daily Texas newspapers. The second goal of this study is to analyze the newspapers' content, specifically relating to President Barack Obama's most recent immigration speech given in November 2014. Obama's speech expressed his interest in temporarily protecting undocumented parents of U.S. citizens or legal permanent residents, while making greater efforts to deport unlawful immigrants who could be considered dangerous. The social responsibility theory is consistent with this study's research question and hypotheses because it sets a standard of what the news media should owe the public, such as employing a diverse set of journalists and fairly reporting on a minority-related issue. Thus, this thesis identifies the composition of diversity in Texas newsrooms and the pertinence of understanding how a minority-related issue is covered in the top ten daily Texas newspapers.Item Interdisciplinary studies portfolio(2012-05) Weinert, Philip M.; Morse, Audra; Davis, Donna F.; Heuman, Amy N.For completion of my Masters degree I must complete a portfolio comprised of specific works of which I think would show growth and development as a collegiate scholar. I have chosen for my portfolio a composition of a case study analysis, research proposal, a term paper, and an overall reflection to show the growth I have developed over the last two and a half years. The three papers which I have included I have written for several of the many graduate courses I have taken while achieving my Masters of Science in Interdisciplinary Studies.Item Interference alignment from theory to practice(2013-05) El Ayach, Omar; Heath, Robert W., Ph. D.Wireless systems in which multiple users simultaneously access the propagation medium suffer from co-channel interference. Untreated interference limits the total amount of data that can be communicated reliably across the wireless links. If interfering users allocate a portion of the system's resources for information exchange and coordination, the effect of interference can be mitigated. Interference alignment (IA) is an example of a cooperative signaling strategy that alleviates the problem of co-channel interference and promises large gains in spectral efficiency. To enable alignment in practical wireless systems, channel state information (CSI) must be shared both efficiently and accurately. In this dissertation, I develop low-overhead CSI feedback strategies that help networks realize the information-theoretic performance of IA and facilitate its adoption in practical systems. The developed strategies leverage the concepts of analog, digital, and differential feedback to provide IA networks with significantly more accurate and affordable CSI when compared to existing solutions. In my first contribution, I develop an analog feedback strategy to enable IA in multiple antenna systems; multiple antennas are one of IA's key enabling technologies and perhaps the most promising IA use case. In my second contribution, I leverage temporal correlation to improve CSI quantization in limited feedback single-antenna systems. The Grassmannian differential strategy developed provides several orders of magnitude in CSI compression and ensures almost-perfect IA performance in various fading scenarios. In my final contribution, I complete my practical treatment of IA by revisiting its performance when CSI acquisition overhead is explicitly accounted for. This last contribution settles the viability of IA, from a CSI acquisition perspective, and demonstrates the utility of the proposed feedback strategies in transitioning interference alignment from theory to practice.Item LDPC code-based bandwidth efficient coding schemes for wireless communications(2009-06-02) Sankar, HariThis dissertation deals with the design of bandwidth-efficient coding schemes with Low-Density Parity-Check (LDPC) for reliable wireless communications. Code design for wireless channels roughly falls into three categories: (1) when channel state information (CSI) is known only to the receiver (2) more practical case of partial CSI at the receiver when the channel has to be estimated (3) when CSI is known to the receiver as well as the transmitter. We consider coding schemes for all the above categories. For the first scenario, we describe a bandwidth efficient scheme which uses highorder constellations such as QAM over both AWGN as well as fading channels. We propose a simple design with LDPC codes which combines the good properties of Multi-level Coding (MLC) and bit-interleaved coded-modulation (BICM) schemes. Through simulations, we show that the proposed scheme performs better than MLC for short-medium lengths on AWGN and block-fading channels. For the first case, we also characterize the rate-diversity tradeoff of MIMO-OFDM and SISO-OFDM systems. We design optimal coding schemes which achieve this tradeoff when transmission is from a constrained constellation. Through simulations, we show that with a sub-optimal iterative decoder, the performance of this coding scheme is very close to the optimal limit for MIMO (flat quasi-static fading), MIMO-OFDM and SISO OFDM systems. For the second case, we design non-systematic Irregular Repeat Accumulate (IRA) codes, which are a special class of LDPC codes, for Inter-Symbol Interference (ISI) fading channels when CSI is estimated at the receiver. We use Orthogonal Frequency Division Multiplexing (OFDM) to convert the ISI fading channel into parallel flat fading subchannels. We use a simple receiver structure that performs iterative channel estimation and decoding and use non-systematic IRA codes that are optimized for this receiver. This combination is shown to perform very close to a receiver with perfect CSI and is also shown to be robust to change in the number of channel taps and Doppler. For the third case, we look at bandwidth efficient schemes for fading channels that perform close to capacity when the channel state information is known at the transmitter as well as the receiver. Schemes that achieve capacity with a Gaussian codebook for the above system are already known but not for constrained constellations. We derive the near-optimum scheme to achieve capacity with constrained constellations and then propose coding schemes which perform close to capacity. Through linear transformations, a MIMO system can be converted into non-interfering parallel subchannels and we further extend the proposed coding schemes to the MIMO case too.Item Network and Index Coding with Application to Robust and Secure Communications(2011-02-22) El Rouayheb, Salim Y.Since its introduction in the year 2000 by Ahlswede et al., the network coding paradigm has revolutionized the way we understand information flows in networks. Traditionally, information transmitted in a communication network was treated as a commodity in a transportation network, much like cars on highways or fluids in pipes. This approach, however, fails to capture the very nature of information, which in contrast to material goods, can be coded and decoded. The network coding techniques take full advantage of the inherent properties of information, and allow the nodes in a network, not only to store and forward, but also to "mix", i.e., encode, their received data. This approach was shown to result in a substantial throughput gain over the traditional routing and tree packing techniques. In this dissertation, we study applications of network coding for guarantying reliable and secure information transmission in networks with compromised edges. First, we investigate the construction of robust network codes for achieving network resilience against link failures. We focus on the practical important case of unicast networks with non-uniform edge capacities where a single link can fail at a time. We demonstrate that these networks exhibit unique structural properties when they are minimal, i.e., when they do not contain redundant edges. Based on this structure, we prove that robust linear network codes exist for these networks over GF(2), and devise an efficient algorithm to construct them. Second, we consider the problem of securing a multicast network against an eavesdropper that can intercept the packets on a limited number of network links. We recast this problem as a network generalization of the classical wiretap channel of Type II introduced by Ozarow and Wyner in 1984. In particular, we demonstrate that perfect secrecy can be achieved by using the Ozarow-Wyner scheme of coset coding at the source, on top of the implemented network code. Consequently, we transparently recover important results available in the literature on secure network coding. We also derive new bounds on the required secure code alphabet size and an algorithm for code construction. In the last part of this dissertation, we study the connection between index coding, network coding, and matroid linear representation. We devise a reduction from the index coding problem to the network coding problem, implying that in the linear case these two problems are equivalent. We also present a second reduction from the matroid linear representability problem to index coding, and therefore, to network coding. The latter reduction establishes a strong connection between matroid theory and network coding theory. These two reductions are then used to construct special instances of the index coding problem where vector linear codes outperform scalar linear ones, and where non-linear encoding is needed to achieve the optimal number of transmission. Thereby, we provide a counterexample to a related conjecture in the literature and demonstrate the benefits of vector linear codes.Item Symmetrical public relations surgery : two-way symmetrical suggestions for physicians and the medical device industry(2012-05) Faulk, Eric Jonathan; Warner, David C.; Anderson, Ronald B.The public relations field is rapidly adopting two-way symmetrical communications as a way to achieve excellence and win-win solutions for multiple publics. This paper focuses on activism and industry public relations approaches involving a group of expert physicians in Houston and the medical devices industry. After exploring two-way symmetrical communications and the Excellence Theory of Public Relations, the paper explores these physicians’ viewpoints and provides an overview of the medical device industry. The discussion then provides public relations suggestions for the physicians to symmetrically approach the industry to create change. Next, the paper recommends how the medical device industry can respond to work with the physicians and to prevent possible public relations damage and crisis. The paper concludes by expressing the importance of applying symmetrical communications methods to solve challenges and create win-win solutions.Item Televising architecture : media, public engagement, and design in America(2014-05) Dodd, Samuel Tommy; Cleary, Richard LouisStarting in the 1940s, the cultural revolution associated with the popularity of television placed new demands on how and where designers communicated the value of their work with the American public. "Televising Architecture" explains how architects, planners, and other design professionals used television as a communication technology and as a cultural platform for shaping public opinion on the built environment. Each of the six chapters describes a specific purpose and context for the application of television to architectural practice. I consider public affairs programs produced by the American Institute of Architects; the use of closed-circuit television for space simulations; public service announcements meant to offset negative coverage on urbanism; interactive television projects that elicited community participation in planning; and PBS mini-series on the history of American architecture. I conclude by discussing Home and Garden Television (HGTV) as a lesson in media convergence for design professionals in the twenty-first century. "Televising Architecture" provides a new way to understand architecture not as a text, image, or built object, but as a complex system of communication models — including representation, negotiation, mediation, and participation — that occur between design experts and the public at large. I draw from the work of media and technology scholars who treat media as sites of negotiation and convergence. One of my primary methods is to analyze the largely untapped archive of architectural images, texts, and sound-bites found in television programming. I do so by examining programs themselves, including frame-by-frame analysis to identify what the programs communicated through visual tropes and camera and editing techniques, and a textual analysis, drawing on transcripts, program summaries, and press coverage. As a result, Televising Architecture provides historical perspectives— and a series of media lessons— for understanding the practice of architecture in our current digital culture, wherein architects must navigate a new media environment in the pursuit of social relevance.