Techniques used to model a field-effect transistor's equivalent circuit parameters are investigated and applied to an on-wafer AlGaN/GaN HFET using high-frequency S-parameters. Analysis of a THRU line allowed substrate permittivity characterization, improving parasitic capacitance estimation. Drain-source output admittance dispersion was observed in the measured devices. This dispersion phenomena was attributed to parallel conduction and was primarily present for low drain-source bias. Dispersion complicated parameter calculation and required modification of commonly used model extraction techniques. Effective mobility was also estimated by only using information contained in the S-parameter measurements. Small-signal parameter temperature dependence was also investigated to determine each parameter's associated temperature coefficient.

Performances of closed-loop control systems operated over a data network are typically degraded by network-induced delays. Furthermore, the closed-loop control systems can become unstable. The purpose of this research has been to develop a control methodology to handle network-induced delay effects using optimal gain scheduling on existing controllers. The proposed gain scheduling technique adapts controller gains externally by modifying a controller output to enable the controller for uses over a data network. Since existing controllers can still be utilized, the proposed methodology can reduce control system reinstallation and replacement costs. First, the effectiveness of the proposed gain scheduling technique on networked DC motor speed control using a PI (Proportional-Integral) controller is investigated. Also, the concept of network traffic condition measurement to select optimal controller gains is presented. Then, a middleware framework to measure network traffic conditions on an IP network based on delays and delay variations and to modify controller gains is described. Suggestion of using neural network in the gain scheduling scheme is also given. Finally, the gain scheduling technique with the middleware framework is then extended to mobile robot path-tracking control.

Multiple-antenna systems have generated tremendous research interest in the recent past mainly because of their promise of significant gains in capacity and performance as compared to single-antenna systems. Most work on multiple antennas has focused on the design of coding and modulation schemes, channel estimation algorithms and decoding architectures. Information is sent by the transmitter as electromagnetic (EM) waves which subsequently undergo multipath fading before they reach the receiver. The EM properties of the antennas and the nature of the scattering environment jointly impact the performance of communication algorithms. However, there are relatively few works in the literature that consider this interrelation in the design of transmitter-receiver architectures. In this dissertation we study three such problems: the dependence of capacity on the EM properties of antennas and the scattering environment, the limits on performance of parameter estimation algorithms at the receiver and finally, the fundamental limits on the capacity that volume-limited multiple-antenna systems can achieve. We first consider the joint design of multi-element antennas and capacity-optimal signalling for a multiple-input multiple-output (MIMO) wireless channel. We use EM theory and ray-tracing methods to derive a channel propagation model for antennas that can detect or excite more than one component of the electric field vector (known as vector antennas) in a discrete-multipath channel environment. This model provides insights into the inter-relation between the spatial multiplexing gain and the nature of the multipath environment for vector antennas. We then generalize this model to the case of antennas with more general electric-field patterns in a fading environment with clusters of scatterers. Capacity-optimal signalling and the impact of antenna electric field patterns on capacity are studied. We focus on joint antenna-signal design and derive optimality criterion for multi-element antenna systems for maximizing the ergodic capacity. We show that antennas that have orthogonal and equal norm electric-field patterns maximize the ergodic capacity. Vector antennas satisfy this criteria, but a uniform linear array does not. We next consider the problem of positioning and direction-of-arrival (DOA) estimation with ultrawideband (UWB) vector antennas. Due to the wideband nature of the antenna response and directional sensitivity of vector antennas, precise ranging and DOA estimation of a transmitting source can be jointly performed. We first derive a frequency-domain Cramer-Rao Bound formula in the asymptotic case of a large number of observation samples in stationary noise. We apply this formula to two UWB vector antennas and obtain closed-form lower-bound expressions for the ranging and DOA error covariances. A criterion based on the linearized confidence region is used to design signal pulses that give uniform resolving capability to the antennas for any DOA. Finally, we consider the fundamental capacity limits that a multi-element antenna system that is restricted to occupy a finite volume can achieve. For simplicity, we consider the problem of a spherical volume current source radiating into space with a receiver in the far-field capable of detecting the electric field on a concentric spherical surface. The system is first described as a linear operator, and the exact singular values of the system are derived in closed form. The singular values and hence the capacity is shown to depend on the transmitter volume only through its radius. We calculate the capacity of such a system, and provide capacity formulas that are accurate at high signal-to-noise ratio.

Development of digital core chips poses serious challenges to the power supply design. High performance switching DC-DC converter must meet requirements of high current, low voltage tolerance, fast transient response, high power efficiency, small profile and low cost. The conventional PWM control with constant switching frequency has limitation to improve both transient response and power efficiency because there is a conflicting requirement on switching frequency. The control scheme with variable frequency has promising features to achieve better overall performance, but the issues in the reported design approaches limit their usefulness in the practical applications. This dissertation reviews and summarizes the issues and the design considerations in the high current switching DC-DC converters. To improve the system performance, novel control architecture with variable switching frequency and novel implementation of the integrated controller are proposed in this dissertation. The proposed control architecture is modeled and analyzed. Fully differential circuits are designed to implement the control core functions. The design methodology and the design considerations are discussed. The control concept and the proposed circuits are verified by the prototype controller chip.

Time-frequency effects in wireless communication systems caused by narrowband resonances and coupled with device nonlinearities are revealed as new sources of co-site interference, exploited for the metrology of bandpass circuits, and employed to linearize amplitude-modulated transmissions. The transient properties of bandpass filters are found to last much longer than traditional time/bandwidth rules-of-thumb. The cause of this long-tail behavior is attributed to the coupled-resonator structure of the filter circuit. A solution method which uses lowpass prototyping is developed to reduce, by a factor of two, the complexity of the differential equation set describing a narrowband filter's transient response. Pulse overlap caused by the frequency dependence of long tails produced by filters is shown to cause intersymbol interference and intermodulation distortion in RF front-ends during frequency-hopped communications. The same properties which cause the ISI and IMD are used to develop three new transient methods for measuring resonant circuit parameters and a one-port method for extracting the operating band of a filter. A new signal-processing technique which combines time- and frequency-selectivity, Linear Amplification by Time-Multiplexed Spectrum, is developed to reduce IMD associated with amplitude modulation. Distortion reduction is demonstrated experimentally for multisines up to 20 tones.

This dissertation deals with research into the design and implementation of a new wide field of view retroreflector device for autonomous mobile robot communication. In order to demonstrate effective and efficient optical communication for robots, the research had first to address the problem of expanding the field of view of retroreflectors. Experimentation shows that the device is beneficial for robotics navigation and localization, and for underwater optical communication. The retroreflector is similar to other conventional cat?s-eye retroreflector designs, but the use of a fisheye lens and compensating lens to collimates the light before it enters a spherical retroreflector was found facilitate a wider field of view. Using this approach the retroreflector FOV was increased to 180 degrees although at the expense of divergence angle due to spherical aberration. The combination of both a laser transceiver unit and the retroreflector formed a very useful device for several short-range wireless optical communication scenarios including robot to robot communication in situations whereby navigation and localization was executed for collaborating robots and potentially underwater optical communication in turbid water. For ease in testing and implementation visible and near infrared wavelengths were used with a relatively low speed, polarization independent, liquid crystal modulator. While the data rate and range of the tested system are limited, the results of the project indicate that with high speed optical modulators and a suitable pointing and tracking system that collaborative robot activities and robot to robot communications can be substantially advance by using free space optical communications with wide field of view retroreflectors.

Due to correlated fading in frequency hopping (FH) wireless communication systems, it is possible to predict the future channel state information (CSI) for one frequency based on the channel observations of other frequencies. As a result, the performance of slow FH systems can be improved by utilizing adaptive transmission techniques. We propose the optimal Minimum Mean Square Error (MMSE) Long Range Prediction algorithm for slow FH systems that employ coherent detection. A recursive autocorrelation update method and a simplified prediction algorithm are explored to reduce the complexity. Statistical model of the prediction accuracy is developed and used in the design of the reliable adaptive transmission systems. We investigate the performance of adaptive transmission for high-speed data transmission in SFH systems based on the proposed Long Range Prediction algorithms. For slow frequency hopping communications in the presence of partial-band interference, we propose to employ adaptive transmitter frequency diversity and adaptive modulation to mitigate the effects of partial-band interference and fading. Both standard Jakes model and realistic physical model are used to test the performance. Analysis and simulation results show that significant performance gains can be achieved relative to non-adaptive methods.

The use of a shared network, as a communication channel, in a Networked Control System (NCS) can provide an economical and easily accessible resource. However, it can also result in performance degradation or even destabilization of the control system. Similar effects may arise from different operating conditions of the system. In this research, the effect of the network is compared with the effects exerted by three other parameters in an Unmanned Ground Vehicle (UGV) path-tracking problem. The system?s performance is quantified by means of three characteristics: the deviation error, the system?s runtime and the error-time product. Design of Experiments (DOE) and regression analysis are utilized to appropriately collect and analyze experimental data. For the ranges of variation studied, it is shown that the system is two times more sensitive to the speed of the vehicle than to network?s delay. The effect of the look-ahead distance is shown to be similar to the network?s delay effect, indicating a potential control strategy to alleviate the network?s effect by appropriately adjusting the look-ahead distance. The above results are drawn with respect to the completion time and the error-time product characteristics of the system. The deviation error is shown to have a more complex relationship with the four parameters studied and their effects can only be calculated locally, based on the operating conditions of the system.

Stroke is the third leading cause of death in the United States. Nearly 700,000 people suffered from stroke last year and two thirds of them survived but were left with any number of disabilities, one such disability is upper extremity hemiplegia. If the hand and arm doesn?t have therapy immediately after stroke, it will lose it power and muscle control, resulting in a claw like appearance and loss of function. Activities of the patient daily living will be significantly effected. Current therapy on the affected limb in the hospital is expensive and difficult to manage due to the limited amount of resources compared to the number of patients. We introduce a pneumatic actuated wearable hand and forearm device in this thesis. It is designed according to the hand and arm kinematics. It can help the patients keep power on each finger and help maintain the coordination of different fingers to achieve daily living movements. It consists of forearm brace, rehabilitation glove and artificial muscles. The custom made artificial muscles also known as McKibben Artificial Muscles are used in antagonistic pairs to control the fingers flexion and extension. The rehabilitation device is small, lightweight, home-based, and has large force capabilities. It is also affordable to the patients due to the specially designed low-cost artificial muscles. The rehabilitation device was controlled by solenoid valves in conjunction with a Mitsubishi M32/83C 16-bit micro controller. Experiments on the pneumatic elbow brace have shown that it is capable of moving each finger from full extension to flexion, to perform actions like pinching and allows the coordinated movement of two fingers.

Simulation of Radio Frequency Switches used in the cellular phone industry is the main focus of this study. The RF pHEMT?s used in an antenna switch for multiband cell phone circuits requires the use of an accurate model during simulation of the RF system. The pHEMT model extracted in this study utilizes theoretical methods within the extraction software and an analysis of simulated data and measured data. This study describes the techniques of calibration, model extraction, and data analysis.