Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 151-153). Also available via the Internet.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains ix, 124 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 119-124).

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains ix, 60 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 59-60).

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xi, 84 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 75-79).

Different from multiple-input multiple-output (MIMO) systems, a major challenge for cooperative communications is the problem of synchronization because multiple transmissions undertaken by cooperative systems may not be synchronized in time and/or frequency. With synchronization errors, conventional space-time (ST) codes may not be directly applicable any longer. To tackle the problem of timing synchronization, space-frequency (SF) coded orthogonal frequency division multiplexing (OFDM) cooperative systems have recently been proposed to achieve asynchronous diversity due to their insensitivity to timing errors. However, these systems still need to face the problem of multiple carrier frequency offsets (CFOs). Since each node in a cooperative system is equipped with its own oscillator, the received signals from different relay nodes may have multiple CFOs which cannot be compensated simultaneously at the destination node. For SF coded OFDM cooperative systems, this problem becomes more complicated because CFOs can lead to inter-carrier interference (ICI). To address this challenge, in this thesis we consider the signal detection problem in cooperative systems having multiple CFOs. / First, we investigate the effect of multiple CFOs on two classic ST codes. They are delay diversity and the Alamouti code. For delay diversity, we find that both its achieved diversity order and diversity product are not decreased by multiple CFOs arising from maximum-likelihood (ML) detection. For the Alamouti code, the diversity product may be decreased by multiple CFOs. In the worst case situation, full diversity order 2 cannot be achieved. / For deeper insights into the SF coded communication system with multiple CFOs, we then carry out diversity analysis. By treating the CFOs as part of the SF codeword matrix, we show that if all the absolute values of normalized CFOs are less than 0.5, then the full diversity order for the SF codes are not affected by the multiple CFOs in the SF coded OFDM cooperative system. We further prove that this full diversity property can still be preserved if the zero forcing (ZF) method is used to equalize the multiple CFOs. This method, by some reasonable approximations, is actually equivalent to the MMSE-F detection method. To improve the robustness of the SF codes to multiple CFOs, we propose a novel permutation method. With this method, the achieved diversity order of SF codes remains the same even when the absolute values of normalized CFOs are equal to or greater than 0.5. To reduce computational complexity, we further propose two full diversity achievable detection methods, namely the ZF-ML-Zn and ZF-ML-PIC detection methods, which are suitable for the case when the ICI matrix is singular. / In summary, in this study, we demonstrate that with proper design, the SF coded OFDM approach can be made robust to both timing errors and CFOs in a cooperative communication system. / Since OFDM systems are robust to timing errors, we turn to an SF coded cooperative communication system with multiple CFOs, where the SF codes are rotational based and can achieve both full cooperative and full multipath diversity orders. We begin with the traditional way of ICI mitigation. To preserve the performance of the SF code, we suggest increasing the SINR of each subcarrier but not equalizing the SF precoding matrix. By exploiting the structure of the SF codes, we propose three signal detection methods to deal with the multiple CFOs problem in SF coded OFDM systems. They are the minimum mean-squared filtering (MMSE-F) method, the two-stage simple frequency shift Q taps (FS-Q-T) method, and the multiple fast Fourier transform (M-FFT) method, all of which offer different tradeoffs between performance and computational complexity. Our simulation results indicate that the proposed detection methods perform well as long as the CFOs between nodes are small. / Tian, Feng. / Adviser: Ching Pak-Chung. / Source: Dissertation Abstracts International, Volume: 71-01, Section: B, page: 0559. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 146-160). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.

Wireless communication continues to make a profound impact upon our daily lives. The oft-touted benefits of high data rates and improved reliability via wireless communication are limited by its inherent drawbacks, including path loss, fading and interference. One promising strategy for overcoming these problems is to deploy nodes in the region between a transmitter and its intended receiver. These intermediate nodes can improve communication for this transmitter-receiver pair by receiving a transmitted message, processing it and relaying the processed output to the receiver. This transmission strategy, known as relay-assisted communication, can be especially beneficial when the transmitter-receiver pair are either separated by a large distance or when a large obstruction blocks the path between them. In a reasonably dense network, several relays may be available to assist a particular transmitter-receiver pair. Deciding which relays should forward the transmitted message is actually quite difficult. For example, the relay with the best physical-layer channel gain to the destination may also be running low on battery power. Another relay may have a good physical-layer channel gain to the destination and a reasonable amount of remaining battery power, but its queue may be full of messages from other transmitters, so it cannot forward a newly arrived message within a given delay constraint. Thus, optimal relay selection entails carefully balancing all system parameters, which is prohibitively complex in current wireless systems. This dissertation provides novel results for dealing with the relay selection problem in two distinct types of wireless systems. First, several selection algorithms are designed for single-antenna wireless networks, including a decentralized random access-based strategy and centralized methods that are based on throughput maximization and downlink user scheduling. Second, selection algorithms based on transmission hop length are designed for multipleantenna wireless networks. The presented strategies for both single-antenna and multiple-antenna relaying are highly intuitive, as they allow for concise descriptions, making them amenable to practical implementation. Also, the presented strategies illustrate the importance of application-specific design, since each of them yields good performance by focusing on a small set of system parameters. For example, observed latency is of paramount importance for wireless networks that support a significant level of video traffic. / text

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 49 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 47-49).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references and index.

Designers of low-power radio systems for use in urban areas would benefit from the capability for accurate computer-based predictions of signal loss due to shadowing. This thesis is intended to fill a need for prediction methods that exploit a building database and consider the three-dimensional profile of the radio path. Models are presented that allow the application of Fresnel-Kirchoff diffraction theory to arbitrarily oriented buildings of simple shapes. Building location information used by the diffraction models is in a form compatible with a geographic information systems (GIS) database. Diffraction screens are constructed at all building edges, including those of both horizontal and vertical orientations, in order to consider all possible diffractions and to compute field contributions often ignored. Multiple buildings and edges of the same building that introduce multiple successive diffractions are considered with a rigorous, recursive application of the diffraction theory that requires sampling the field distribution in each aperture. Robust and computationally efficient numerical methods are applied to solve the diffraction integrals. The software implementation of these methods is tested with example runs and comparisons with 914 MHz continuous-wave measurements taken on the Virginia Tech campus. / Master of Science

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