In single-input multiple-output (SIMO) systems based on orthogonal frequency division multiplexing (OFDM), adaptive beamforming at the receiver side can be used to combat the effect of directional co-channel interference (CCI). Since pilot-aided beamforming suffers from consuming precious channel bandwidth, there has been much interest in blind beamforming approaches that can adapt their weights by restoring certain properties of the transmitted signals. Within this class of blind algorithms, the recursive least squares constant modulus algorithm (RLS-CMA) is of particular interest due to its good overall CCI cancelation performance and fast convergence. Nevertheless, the direct use of RSL-CMA within a SIMO-OFDM receiver induces considerable computational complexity, since a distinct copy of the RLS-CMA must be run on each individual sub-carriers. In this thesis, we present two approaches to reduce the computational complexity of SIMO-OFDM beamforming based on the RLS-CMA, namely: frequency interpolation and distributed processing. The former approach, which exploits the coherence bandwidth of the broadband wireless channels, divides the sub-carriers into several contiguous groups and applies the RLS-CMA to a selected sub-carrier in each group. The weight vectors at other frequencies are then obtained by interpolation. The distributed processing approach relies on the partitioning of the receiving array into sub-arrays and the use of a special approximation in the RLS-CMA. This allows a partial decoupling of the algorithm which can then be run on multiple processors with reduced overall complexity. This approach is well-suited to collaborative beamforming i~ multi-node distributed relaying. Through numerical simulation experiments of a SIMO-OFDM system, it is demonstrated that the proposed modifications to the RLS-CMA scheme can lead to substantial computational savings with minimal losses in adaptive cancelation performance.

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Wireless systems that have traditionally been designed using a layered approach have seen a recent paradigm shift to a cross-layered approach where the interactions between two or more layers are considered explicitly in an integrated framework. This dissertation presents new methodologies that aim to improve the performance of wireless systems through consideration of cross-layer based design. The physical (PHY) and the medium access control (MAC) layers are the primary layers responsible for data transmission and user selection/control, respectively, in wireless systems. This dissertation begins with an analysis illustrating the use of multiple antennas and antenna arrays at. the PHY layer. A framework combining space-time block coding and beamforming for uplink in a wireless systems is con¬sidered for studying the trade-offs between antennas and antenna arrays at the receiver. Results indicate that in high noise environments the diversity achieved by using a large number of antennas combats bit error rate (BER) more efficiently than beamforming. On the other hand, in low noise environments beamforming plays an important role in reducing BER by minimizing the effect of interference from other co-channel users. Two approaches of cross-layer design that are currently available are the bottom-up and top-down approaches. The bottom-up approach uses the PHY laver infor¬mation at the MAC and higher layers to make decisions that affect the system performance. Following a bottom-up approach, a new scheduling algorithm is designed that uses the channel state information and direction of arrival information of mobile users to efficiently schedule users for service. Both semi-analytical (based on the probability density and cumulative distribution functions) and numerical frameworks are used to compare the performance of this algorithm with the traditional round-robin and greedy scheduling algorithms. Both the numerical and semi-analytical frameworks which are shown to be consistent with each other yield improved system capacity for the proposed algorithm compared to the traditional algorithms. This is the result of explicitly considering the angular location of mobile users around the base station that results into the reduced interference between simultaneously served users on one other. The effect of channel availability on the scheduling algorithms is also investigated within a queuing framework and the results indicated that the system performance is also dependent on channel availability and traffic conditions. A top-down approach is based on modifying the PHY layer to support the require¬ments or protocols used at the MAC layer to improve system throughput. Following a top-down approach, a new methodology is presented that reduces null depths of a given beam to address the hidden beam problem in IEEE 802.11 systems. The hidden beam problem occurs in carrier sensing multiple access (CSMA) systems when mobile users lying in deep nulls are unable to sense an ongoing downlink transmission and start transmitting data in an uplink. The modified beam with reduced null depths is compared with the original beam in terms of reducing the hidden beam problem when used in non-persistent CSMA systems. The modified beam is shown to improve the throughput of a slotted non-persistent CSMA system significantly when compared to original beam with relatively small changes to directivity and half power beamwidth. The bottom-up and top-down approaches used in this dissertation illustrate that by jointly addressing the PHY and MAC layer issues in an integrated cross-layer framework the performance of wireless systems can be significantly improved.

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The optics and photonics development is currently driven towards nanometer scales. However, diffraction imposes challenges for this development because it prevents confinement of light below a physical limit, commonly known as the diffraction limit. Several implications of the diffraction limit include that conventional optical microscopes are unable to resolve objects smaller than 250nm, and photonic circuits have a physical dimension on the order of the wavelength. Metals at optical frequencies display collective electron oscillations when excited by photon energy, giving rise to the surface plasmon modes with subdiffractional modal profile at metal-dielectric interfaces. Therefore, metallo-dielectric structures are promising candidates for alleviating the obstacles due to diffraction. This thesis investigates a particular branch of plasmonic structures, namely plasmonic antennas, for the purpose of optical imaging and sensing applications. Plasmonic antennas are known for their ability of dramatic near-field enhancement, as well as effective coupling of free-space radiation with localized energy. Such properties are demonstrated in this thesis through two particular applications. The first one is to utilize the interference of evanescent waves from an array of antennas to achieve near-field subdiffraction focusing, also known as superfocusing, in both one and two dimensions. Such designs could alleviate the tradeoffs in the current near-field scanning optical microscopy by improving the signal throughput and extending the imaging distance. The second application is to achieve more efficient radiation from single-emitters through coupling to a highly directive leaky-wave antenna. In this case, the leaky-wave antenna demonstrates the ability of enhancing the directivity over a very wide spectrum.

The optics and photonics development is currently driven towards nanometer scales. However, diffraction imposes challenges for this development because it prevents confinement of light below a physical limit, commonly known as the diffraction limit. Several implications of the diffraction limit include that conventional optical microscopes are unable to resolve objects smaller than 250nm, and photonic circuits have a physical dimension on the order of the wavelength. Metals at optical frequencies display collective electron oscillations when excited by photon energy, giving rise to the surface plasmon modes with subdiffractional modal profile at metal-dielectric interfaces. Therefore, metallo-dielectric structures are promising candidates for alleviating the obstacles due to diffraction. This thesis investigates a particular branch of plasmonic structures, namely plasmonic antennas, for the purpose of optical imaging and sensing applications. Plasmonic antennas are known for their ability of dramatic near-field enhancement, as well as effective coupling of free-space radiation with localized energy. Such properties are demonstrated in this thesis through two particular applications. The first one is to utilize the interference of evanescent waves from an array of antennas to achieve near-field subdiffraction focusing, also known as superfocusing, in both one and two dimensions. Such designs could alleviate the tradeoffs in the current near-field scanning optical microscopy by improving the signal throughput and extending the imaging distance. The second application is to achieve more efficient radiation from single-emitters through coupling to a highly directive leaky-wave antenna. In this case, the leaky-wave antenna demonstrates the ability of enhancing the directivity over a very wide spectrum.

Includes bibliographies. / xix, [252] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This research addresses probe fed classical rectangular microstrip antenna elements and arrays, that are fabricated on substrate materials with various thicknesses and relative permittivities. Formulae are developed for calculating the patch dimensions, the resonant input resistance, the resonant frequency, the bandwidth and the radiation patterns of elements, as well as the mutual coupling coefficients of arrays. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1996

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Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 169-173).