No / Two novel reduced-size, printed spiral antennas are proposed for use in personal communications mobile terminals exploiting the “big low earth orbit” (Big-LEO) satellite system (uplink 1.61–1.63 GHz; downlink 2.48–2.5 GHz). The two proposed antenna give 3.12―6.25% bandwidth at lower resonant mode of 1600MHz, while at the higher resonant mode of 2450MHz a bandwidth of around 6% is obtained. The experimental and simulated return losses of the proposed antennas show good agreement. The computed and measured gains, and axial ratios are presented, showing that the performance of the proposed two antennas meets typical specifications for the intended applications.

Physiological process models, productivity studies, and wildlife abundance studies all require accurate representations of tree crowns. In the past, geometric shapes or flexible mathematical equations approximating geometric shapes were used to represent crown profiles. Crown profile of loblolly pine (<I>Pinus taeda</I> L.) was described using single-regressor, nonparametric regression analysis in an effort to improve crown representations. The resulting profiles were compared to more traditional representations. Nonparametric regression may be applicable when an underlying parametric model cannot be identified. The modeler does not specify a functional form. Rather, a data-driven technique is used to determine the shape a curve. The modeler determines the amount of local curvature to be depicted in the curve. A class of local-polynomial estimators which contains the popular kernel estimator as a special case was investigated. Kernel regression appears to fit closely to the interior data points but often possesses bias problems at the boundaries of the data, a feature less exhibited by local linear or local quadratic regression. When using nonparametric regression, decisions must be made regarding polynomial order and bandwidth. Such decisions depend on the presence of local curvature, desired degree of smoothing, and, for bandwidth in particular, the minimization of some global error criterion. In the present study, a penalized PRESS criterion (PRESS*) was selected as the global error criterion. When individual- tree, crown profile data are available, the technique of nonparametric regression appears capable of capturing more of the tree to tree variation in crown shape than multiple linear regression and other published functional forms. Thus, modelers should consider the use of nonparametric regression when describing crown profiles as well as in any regression situation where traditional techniques perform unsatisfactorily or fail. / Ph. D.

The aim of suspension systems in vehicles is to provide the best balance between ride and handling depending on the operating conditions of a vehicle. Active suspensions are far more effective over a variety of different road conditions compared to passive suspension systems. This is because of their ability to store and dissipate energy at different rates. Additionally, they can even provide energy of their own into the rest of the system. This makes active suspension systems an important topic of research in suspension systems. The biggest benefit of having an active suspension system is to be able to provide energy into the system that can minimize the response of the sprung mass. This is done using actuators. Actuator design in vehicle suspension system is an important research topic and a lot of work has been done in the field but little work has been done to estimate the peak control force and bandwidth required to minimize the response of the sprung mass. These two are very important requirements for actuator design in active suspensions. The aim of this study is estimate the peak control force and bandwidth to minimize the acceleration of the sprung mass of a vehicle while it is moving on a compliant surface. This makes the road surface a bi-lateral boundary and hence, the total system is a combination of the vehicle and the compliant road. Generalized vehicle and compliant road models are created so that parameters can be easily changed for different types of vehicles and different road conditions. The peak control force is estimated using adaptive filtering. A least mean squares (LMS) algorithm is used in the process. A case study with fixed parameters is used to show the results of the estimation process. The results show the effectiveness of an adaptive LMS algorithm for such an application. The peak control force and the bandwidth that are obtained from this process can then be used in actuator design. / Master of Science

Variable bit rate (VBR) compressed video traffic, such as live video news, is expected to account for a large portion of traffic in future integrated networks. This real-time video traffic has strict delay and loss requirements, and exhibits burstiness over multiple time scales, thus imposing a challenge on network resource allocation and management. The renegotiated VBR (R-VBR) scheme, dynamically allocating resources to capture the burstiness of VBR traffic, substantially increases network utilization while satisfying any desired quality of service (QoS) requirements. This thesis focuses on the performance evaluation of R-VBR in the context of different R-VBR approaches. The renegotiated deterministic VBR (RED-VBR) scheme, proposed by Dr. H. Zhang et al., is thoroughly investigated in this research using a variety of real-world videos, with both high quality and low quality. A new Virtual-Queue-Based RED-VBR is then developed to reduce the implementation complexity of RED-VBR. Simulation results show that this approach obtains a comparable network performance as RED-VBR: relatively high network utilization and a very low drop rate. A Prediction-Based R-VBR based on a multiresolution learning neural network traffic predictor, developed by Dr. Y. Liang, is studied and the use of binary exponential backoff (BEB) algorithm is introduced to efficiently decrease the renegotiation frequency. Compared with RED-VBR, Prediction-Based R-VBR obtains significantly improved network utilization at a little expense of the drop rate. This work provides evaluations of the advantages and disadvantages of several R-VBR approaches, and thus provides a clearer big picture on the performance of the studied R-VBR approaches, which can be used as the basis to choose an appropriate R-VBR scheme to optimize network utilization while enabling QoS for the application tasks. / Master of Science

Ionic polymer materials are a class of electroactive polymers that have been used in recent applications that take advantage of their large bending deflection. Although these materials have been around since the 1960s, it has only been in the last decade that their electromechanical coupling has been discovered. Because their life as a transducer has been relatively short, the underlying mechanisms for their mechanical motion have not yet been fully characterized. Modeling has been performed with ionic polymers, but there is no existing model, to date, that explains all the physical phenomena associated them. The work presented in this document will contribute to the characterization of these materials. To better understand the dehydration effect of ionic polymers operating in an open air environment, research was performed to help characterize this effect. Through the use of frequency response analysis, trends were established showing how the material's response characteristics varied with time, as the polymer dehydrated. These tests were also run at different humidity levels to assess the impact environmental conditions had on the response. It was shown that lower humidity levels cause the system parameters to shift at a higher rate. The two configurations tested were clamped-free and clamped-clamped, in an effort to bound the performance of the actuators for engineering applications. The clamped-clamped condition also facilitated applying tension to the polymers for evaluation of the dehydrating effects. Several comparisons to beam theory were made throughout the analysis, using it as a baseline condition illustrator. Though qualitative results were obtained with the polymers, there was much discrepancy in quantitative measures. This was to be expected though, because ionic polymers are composite actuators that exhibit nonlinear behavior, while uniform beams are linear. Environmental testing was not all that was done, however. Control techniques were applied to improve the closed-loop performance of the actuators. Using proportional-integral control, it was demonstrated that ionic polymers are capable of tracking reference inputs better than it was previously thought. This result will validate future experimentation with ionic polymers for micro-manipulation applications. The simplicity of integral control also eliminated the need for cumbersome model derivations and control system designs, reducing the time necessary to implement and test an actuator. Through the use of this control algorithm, the closed-loop bandwidth was also characterized for the cantilever and clamped-clamped polymers. / Master of Science

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / A rocket launch, as high dynamics target, was used to demonstrate X-band tracking and also to verify high bit rate frequency planning while demonstrating significant bandwidth reduction with IRIG standard advanced modulation methods. X-band tracking by a modified 8-foot mobile telemetry antenna was excellent. Three separate S-band transmitters with three separate wraparound antennas were launched as a piggyback payload on an Enhanced Orion sounding rocket at White Sands Missile Range (WSMR) to compare the performance of 10 Mbs and 20 Mbs bit error rate (BER) pattern data transmission from CPFSK, FQPSK-JR and ARTM CPM modulation formats under high dynamic conditions. The test is more remarkable in that another S-band wideband spread spectrum signal was also transmitted with good success. These results show that all three modulation methods performed well during ignition and liftoff, low aspect angle (receiving through the rocket motor plume during ascent from a tracker near the launch pad), spin stabilization antenna lobe fades and payload tumbling. Spectrum pictures are provided to show the dramatic reduction in transmission bandwidth from CPFSK to FQPSK-JR to ARTM CPM. Confirmation of the preflight RF adjacent channel interference planning procedures from IRIG 106-05 is described by spectrum pictures and data quality measurements.

Energy conservation in next generation Passive Optical Network system (NG-PON) has gained more and more attention. NG-PON system can not only deliver best-effort data traffic, but also real-time data traffic, e.g. voice and video, that have strict bandwidth, delay, and jitter requirements. To meet the energy and service requirements, a NG-PON system must have energy efficiency and differentiated QoS mechanism built in. Few research efforts have been reported on maximizing energy efficiency while maintaining QoS in the fairly new PON system design. We have extended the Upstream Centric Scheme (UCS-based) scheduling scheme idea into a novel QoS-differentiated energy-efficient PON system consisting of two main modules: firstly, the proposed differentiated QoS analytical model is described in detail to reduce the packet delay in the upstream traffic scheduling. The simulations further demonstrate the QoS metrics of the system: packet delay, bandwidth utilization, dropped packet rate, and queue length. Secondly, a novel analysis is proposed for downstream traffic scheduling with limited service discipline at Optical Line Terminal (OLT) side under the UCS-based Green Bandwidth Allocation (GBA) framework. We, first, derive the mean packet delay expression of this model. Then, the sleep time for each Optical Network Unit (ONU) is derived by setting identical upstream/downstream transmission cycle time. Based on the analytical model, an approach is developed to save the maximum energy in a dynamic PON system while without violating the delay requirement. Moreover, simulation is conducted to verify the developed analytical model and the proposed approach. In the end, considering the differentiated QoS and downstream traffic scheduling, an algorithm of the energy efficient scheduling scheme is proposed as well under the UCS-based GBA.

Energy conservation in next generation Passive Optical Network system (NG-PON) has gained more and more attention. NG-PON system can not only deliver best-effort data traffic, but also real-time data traffic, e.g. voice and video, that have strict bandwidth, delay, and jitter requirements. To meet the energy and service requirements, a NG-PON system must have energy efficiency and differentiated QoS mechanism built in. Few research efforts have been reported on maximizing energy efficiency while maintaining QoS in the fairly new PON system design. We have extended the Upstream Centric Scheme (UCS-based) scheduling scheme idea into a novel QoS-differentiated energy-efficient PON system consisting of two main modules: firstly, the proposed differentiated QoS analytical model is described in detail to reduce the packet delay in the upstream traffic scheduling. The simulations further demonstrate the QoS metrics of the system: packet delay, bandwidth utilization, dropped packet rate, and queue length. Secondly, a novel analysis is proposed for downstream traffic scheduling with limited service discipline at Optical Line Terminal (OLT) side under the UCS-based Green Bandwidth Allocation (GBA) framework. We, first, derive the mean packet delay expression of this model. Then, the sleep time for each Optical Network Unit (ONU) is derived by setting identical upstream/downstream transmission cycle time. Based on the analytical model, an approach is developed to save the maximum energy in a dynamic PON system while without violating the delay requirement. Moreover, simulation is conducted to verify the developed analytical model and the proposed approach. In the end, considering the differentiated QoS and downstream traffic scheduling, an algorithm of the energy efficient scheduling scheme is proposed as well under the UCS-based GBA.

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Modern wireless communication systems call for ultra wideband operations to meet the continuous growth in the number of users of these systems. Since antenna is an integral part of any wireless communication system (transmitter or receiver), designing antennas with good gain over large bandwidth needs to be considered first. To meet the popular demand, wireless communication systems should be as cheap as possible which require antennas with small size, light weight, low profile and low cost, and that are easy to fabricate and assemble. A type of antenna that satisfies most of these requirements is the microstrip antenna. Most of the wideband techniques for microstrip antennas utilize complicated geometries such as stacked multiple metal/dielectric layers, complicated feed arrangements etc., which elude the primary attraction of microstrip antennas. On the other hand, single layer suspended configurations are considered the best choice as these are simple to fabricate and assemble. The objective of this research is to investigate simple microstrip antennas with large bandwidth. A single layer suspended microstrip configuration was chosen for the purpose. In the first part of the research, the bandwidth was increased to about 50% with linear phase characteristics by optimizing the feed configurations while retaining the overall simplicity. This study has resulted in proposing a criterion for obtaining maximum bandwidth in the suspended microstrip configuration. An analytical model has been developed for such an antenna configuration. Although several analytical tools are available for the microstrip antenna analysis, equivalent circuit based approach proves to be a simple one and offers convincingly accurate results. Another advantage of the proposed equivalent circuit modeling scheme is that it is suitable for computer aided design (CAD). In order to make this approach even more useful, the antenna designed in the first part was modified to meet desired specifications such as reduction in the air gap to make the antenna compact, symmetrical patterns, making antenna circularly polarized (LHCP or RHCP) without changing the feed configuration. Nearly symmetrical patterns were obtained throughout the band of operation by modifying the profile of patch close to the feed strip. Circular polarization (CP) operation has been obtained from the basic antenna by cutting a diagonal slot on the radiator patch. Here the slot orientation decides the type of CP i.e., LHCP or RHCP. In this work obtained of 7.1% axial ratio (3dB) bandwidth with other characteristics unaffected. The overall height of the antenna is reduced by 55% by cutting a slot and re-optimizing the feed strip dimensions. These studies emphasize flexibility offered by the design approach in realizing practical antennas for various applications.