Electrical & Computer Engineering Theses and Dissertations

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The Application of the Gyrator Concept to Transistors
(1956) Breeskin, Sol Daniel; Corcoran, George F.; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Sunspots, and the Solar Influence Upon High Frequency Radio Communications
(1960) Jacobs, George; Reed, Henry R.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Study of a UHF Command Destruct Missile Antenna System
(1960) Mullins, Elwood Hatcher; Schuchard, E.A.; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
PRESENTATION OF A NEW HIGH-FREQUENCY COMMUNICATION SYSTEM PERFORMANCE PREDICTION TECHNIQUE
(1965) Gatts, Thomas Fiscus Jr.; Reed, Henry R.; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The prediction technique developed by the National Bureau of Standards has been used extensively by high-frequency communicators. An adaption of this technique is used to demonstrate the type of results obtained when applied to the Buffalo, N.Y. to Boston, Mass. (B/B) link for January and July 1965. A new prediction technique is presented which will allow the HF communicator to predict system performance between the maximum useable frequency (MUF) and the lowest useable frequency (LUF) and which is flexible enough to allow system parameter changes to be made and the effect on the overall system determined. The new technique is demonstrated by applying it to the B/B link for January and July 1965 and displaying the results in the form of relative gain contours, which show the effect on communication capability of reducing the LUF by increasing system gain and the increase in process gain that may be achieved for the purpose of raising the data rate or decreasing transmission error rate. Some of the many applications of the results of this new technique are presented. The results are used: (1) to facilitate the selection of necessary operating frequencies to provide communication throughout a 24-hour period, (2) to estimate the severity and length of occurrence of multipath, (3) to investigate possible frequency adaption, and (4) to investigate possible power adaption.
A Set of Karnaugh Map Manipulation Computer Routines for Use in Logic Design
(1968) Shub, Charles Martin; Marcovitz, Alan B.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The Karnaugh map provides a convenient visual aid for the manipulation of switching functions for both the design engineer and the student of logic design. Algorithms for the minimization of switching functions by the manipulation of information displayed on a Karnaugh map are presented, along with a method of obtaining more information than was previously possible from the Karnaugh map. A dynamic, flexible, and easy to use collection of computer subroutines written in the MAD language to accomplish such manipulations as a subset of an entire logic design system of computer programs is described. A user's manual for the entire system is included, as well as descriptions of the programs used in conjunction with the map manipulation process. Several examples are included.
Some Characteristics of Broadband Delta-Sigma Modulation
(1971) Biegalski, Robert J.; Tretter, Steven; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This paper presents an analysis using correlation techniques of an idealized Delta-Sigma Modulation system. An analytical assumption of errors with a marginally Gaussian distribution is shown to yield accurate results for broadband modulation with a maximum input-output cross correlation. It is also shown that this maximum is greatest for the degenerate case of only "hard limiting" with no feedback and no integration. A case of highly correla~ed inputs for Delta- Sigma Modulation is also discussed to compare it with broad- band performance and "hard limiting."
Bleaching Kinetics of Visual Pigments
(1977) Resnik, Judith Arlene; Zajac, Felix E. III; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
A rapid scanning microspectrophotometer (RMSP) has been developed and utilized to study the photoproducts resulting from the bleaching of rhodopsin in the isolated retina of the frog. The RMSP is capable of measuring absorption spectra at multiple wavelengths within the milliseconds and longer time domain. The unusual characteristic of the instrument is the use of a special cathode ray tube as a measuring light source. Spectral scanning is accomplished electronically, with a sampling interval of 600 microseconds for each waveband. A lock-in amplifier system enables the RMSP to be utilized as either a single or dual beam instrument. The results discussed in this dissertation have shown that hydrogen ion availability is a primary cofactor in determining the relative concentration of the metarhodopsin III photoproduct, with less appearing, in lieu of greater free retinal formation, at low pH levels. Metabolic factors have also been shown to influence the pathways of photoproduct decay. The most significant effect has been observed in nonacidic intracellular environments, with deficiencies in metabolic energy production also favoring the direct formation of free retinal from metarhodopsin II. The half-times of formation and decay of metarhodopsin III have also been observed to vary, depending on the extracellular environment of photoreceptor cells. In general, both halftimes tend to be greater when proportionately more metarhodopsin III 1s formed. The ratio of the two half-times, however, remains relatively constant, except in anoxic conditions, in which the decay half-time is significantly prolonged with respect to the formation half-time. Several problems associated with the control of experimental conditions have been discussed as they relate to photoproduct sequence and kinetics. The elimination of as many metabolic, ionic, and other insufficiently controlled conditions as possible has been pointed out as a necessary requirement for obtaining meaningful quantitative results. In addition, the baseline magnitude of the optical density of the retina, which is, in part, a quantification of light scattering, has been shown to be significantly larger in conditions of low intracellular pH or insufficient substrate supply. The utilization of this parameter as an indirect indicator of the probably sequence of photoproducts has been discussed. In conclusion, this research has provided a greater insight into the mechanisms affecting the later, slow photoproduct processes in isolated retinas. In particular, the interaction of hydrogen ions and metabolic factors influences the pathways of photoproduct decay in isolated retinas, subsequent to metarhodopsin II. The results and methods described here should be useful in establishing a context in which to study the faster mechanisms involved in photochemical and electrical transduction in photoreceptor cells. In addition, these results may become important in understanding the normal and pathological functionings of the eye.
New Methods for the Detection and Interception of Unknown, Frequency-Hopped Waveforms
(1990) Snelling, William Edward; Geraniotis, Evaggelos; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Three new methods for the detection and interception of frequency-hopped waveforms are presented. The first method extends the optimal, fixed-block detection method based on the likelihood ratio to a sequential one based on the Sequential Probability Ratio Test (SPRT). The second method is structured around a compressive receiver and is highly efficient yet easily implemented. The third method is based on the new concept of Amplitude Distribution Function (ADF) and results in a detector that is an extension of the radiometer. The first method presents a detector structured to make a decision sequentially, that is, as each data element is collected. Initially, a purely sequential test is derived and shown to require fewer data for a decision. A truncated sequential method is also derived and shown to reduce the data needed for a decision while operating under poor signal-to-noise ratios (SNRs). A detailed performance analysis is presented along with numerical and Monte Carlo analyses of the detectors. The second method assumes stationary, colored Gaussian interference and presents a detailed model of the compressive receiver. A locally optimal detector is developed via the likelihood ratio theory and yields a reference to which previous ad hoc schemes are compared. A simplified, suboptimal scheme is developed that trades off duty cycle for performance, and a technique for estimating hop frequency is developed. The performance of the optimal and suboptimal detectors is quantified. For the suboptimal scheme, the trade-off with duty cycle is studied. The reliability of the hop frequency estimator is bounded and traded off against duty cycle. In the third method, a precise definition of the ADF is given, from which follows a convolutional relationship between the ADFs of signal and additive noise. A technique is given for deconvolving the ADF, with which signal and noise components can be separated. A detection statistic characterized, yielding a framework on which to synthesize a detector. The detector's performance is analyzed and compared with the radiometer.
Networks for Fast and Efficient Unicast and Multicast Communications
(1992) Lee, Ching-Yi; Oruç, A. Yavuz; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
This dissertation presents new results on networks for high-speed unicast and multicast communications which play key roles in communication networks and parallel computer systems. Specifically, (1) we present past parallel algorithms for routing any one-to-one assignment over Beneš network, we propose new multicasting networks that can efficiently realize any one-to-many assignments, and we give an explicit construction of linear-size expanders with very large expansion coefficients. Our parallel routing algorithms for Beneš networks are realized on two different topologies. Using these algorisms, we show that any unicast assignment that involves )(k) pairs of inputs and outputs can be routed through and n-input Beneš network in O(log2 k+lg n) time without pipelining and O(lg k) time with pipelining if the topology is complete, and in O(lg4k+lg2k lg n) time without pipelining and O(lg3 k+lg k lg n) time with pipelining if the topology is extended perfect shuffle. These improve the best-known routing time complexities of parallel algorithms of Lev et al. and Nassimi and Sahni by a factor of O(lg n). Our multicasting networks uses a very simple self-routing scheme which requires no separate computer model for routing. Including the routing cost, it can be constructed with O(n lg2 n) bit-level constant fanin logic gates, O(lg2 n) bit-level depth, and can realize any multicast assignment in O(lg3 n) bit-level time. These complexities match or are better than those of multicasting networks with the same cost that were reported in the literature. In addition to its attractive routing scheme, our multicasting network is input-initiated and can pipeline multicast assignments through itself. With pipelining, the average routing time for O(lg2 n) multicast assignments can be reduced to O(lg n) which is the best among those of the multicasting networks previously reported in the literature. Our linear-size expanders are explicitly constructed by following a traditional design and analysis technique. We construct a family of linear-size with density 33 and expansion coefficient 0.868. This expansion coefficient is the larges among the linear-size expanders that were similarly constructed. Using these expanders, we also report a family of explicitly constructed superconcentrators with density 208.
Data Acquisition Interface of a VLSI Cochlea Model
(1993) Edwards, Thomas G.; Shamma, Shihab; Electrical Engineering; Digital Repository at the University; University of Maryland (College Park, Md)
Computer models of cochlear processing take exceedingly long times to run, even for short data sets. A data acquisition system was developed for a new switched-capacitor VLSI cochlea model chip, in order to rapidly perform cochleaI processing on digitzed speech samples. The system is capable of processing very long speech samples. Processing is in near-real-time, though it, takes about 2 minutes per second of speech to write the large amount of data to a hard drive. Software has also been developed to convert the output data into a form readable by the ESPS digital signal processing package from Entropic Speech, Inc.
Microwave Nonlinearities in Photodiodes
(1994) Williams, Keith Jake; Dagenais, Mario; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
The nonlinearities in p-i-n photodiodes have been measured and numerically modeled. Harmonic distortion, response reduction, and sinusoidal output distortion measurements were made with two singlefrequency offset-phased-locked Nd: YAG lasers, which provided a source dynamic range greater than 130 dB, a 1 MHz to 50 GHz frequency range, and optical powers up to 10 mW. A semi-classical approach was used to solve the carrier transport in a one-dimensional p-i-n photodiode structure. This required the simultaneous solution of three coupled nonlinear differential equations: Poisson's equation and the hole and electron continuity equations. Space-charge electric fields, loading in the external circuit, and absorption in undepleted regions next to the intrinsic region all contributed to the nonlinear behavior described by these equations. Numerical simulations were performed to investigate and isolate the various nonlinear mechanisms. It was found that for intrinsic region electric fields below 50 kV/cm, the nonlinearities were influenced primarily by the space-charge electric-field-induced change in hole and electron velocities. Between 50 and 100kV/cm, the nonlinearities were found to be influenced primarily by changes in electron velocity for frequencies above 5 GHz and by p-region absorption below 1 GHz. Above 100 kV/cm, only p-region absorption could explain the observed nonlinear behavior, where only 8 to 14 nm of undepleted absorbing material next to the intrinsic region was necessary to model the observed second harmonic distortions of -60 dBc at 1 mA. Simulations were performed at high power densities to explain the observed response reductions and time distortions. A radially inward component of electron velocity was discovered, and under certain conditions, was estimated to have the same magnitude as the axial velocity. The model was extended to predict that maximum photodiode currents of 50 mA should be possible before a sharp increase in nonlinear output occurs. For capacitively-limited devices, the space-charge-induced nonlinearities were found to be independent of the intrinsic region length, while external circuit loading was determined to cause higher nonlinearities in shorter devices. Simulations indicate that second harmonic improvements of 40 to 60 dB may be possible if the photodiode can be fabricated without undepleted absorbing regions next to the intrinsic region.
Analysis of Control Strategies for a Human Skeletal System Pedaling a Bicycle
(1995) Abbott, Scott Bradley; Levine, William S.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The study of human locomotion has gained more attention recently with the availability of better analytic and computational tools with which to examine it. A subject under much study within the field today is the effort to model human motor control systems using control systems methods. Analytic, computational, and experimental studies of locomotion can produce models that provide further insight into the design and function of human systems, as well as provide directions for research into therapies for muscle and nerve related disorders affecting these systems. This thesis examines how computational methods can be utilized to study the functionality of these systems. Building on past research, dynamic models for a human skeletal system pedaling a bicycle are used as a basis for examining various methods of implementing inputs that will control the cycling. Two models are used – a three degree-of-freedom model implementing ideal torque inputs at the hip, knees, and feet, and a one degree-of-freedom model involving inputs at the hip and knee only. Both models are characterized by highly nonlinear dynamics, requiring the use of nonlinear analysis, optimization theory, and computational methods for examination. Control of the one degree-of-freedom model has been addressed in previous work; here, parameterization of the control and the process of learning it is examined. Next, control strategies for the more complex three degree-of-freedom model are developed. Finally, results for upright and recumbent cycling are compared using the three degree-of-freedom model.
Modeling Multi-Band Effects of Hot-Electron Transport in Simulation of Small Silicon Devices by a Deterministic Solution of the Boltzmann Transport Equation Using Spherical Harmonic Expansion
(1998) Singh, Surinder Pal; Mayergoyz, Isaak D.; Goldsman, Neil; Electrical Engineering; University of Maryland (College Park, Md.); Digital Repository at the University of Maryland
Solution of Boltzmann equation by a spherical-harmonic expansion approach is a computationally-efficient alternative to Monte Carlo. In this dissertation we extend this technique to compute the distribution function in multiple bands of silicon, using a multi-band band-structure which is accurate for high energies. A new variable transformation is applied on the spherical harmonic equations. This transformation (a) improves the numerical properties of the quations by enhancing the diagonal dominance of the resulting equations; (b) accounts for exponential dependence of the distribution function on energy as well as electric potential; and (c) opens the possibility of using superior Poisson solvers (d) while retaining the linearity of the original equations intact. The resulting Boltzmann equations are discretized using the current-conserving control-volume approach. The discretized equation are solved using line successive-over-relaxation (SOR) method. Numerical noise in the distribution was analyzed to be originating from the absence of coupling. Noise is removed by using acoustic phonons in inelastic approximation. A novel self-adjoint easy-to-discretize formulation for the inelastic acoustic phonons is developed. A test case of thermal equilibrium for multi-band is derived and used to validate the code. Hole-continuity and Poisson equation were solved along with the multi-band Boltzmann equations. The equations are solved in a Gummel-type decoupled loop. A \nnn\ device is simulated to test the simulator. The simulator is then applied to study a one-dimensional short-base bipolar junction transistor. While these simulations are self-consistent, a two-dimensional sub-micron MOSFET is simulated in a non-self-consistent manner.
Multi-User Security: A Signal Processing and Networking Perspective
(2002) Trappe, Wade; Liu, K.J. Ray; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The advancements in communication and multimedia technologies have paved the way for a new suite of multi-user applications that will allow users to interact. Although the new communication infrastructure makes it easier to reach the end user, it also makes it easier for adversaries to mount attacks against security measures intended to protect data. Thus, there must be mechanisms in place that guarantee the confidentiality and rights of both the customer and the service provider during the delivery of content across future communication networks. This thesis examines security issues related to communications involving more than two participants or adversaries. We approach the problem of multi-user security by developing security measures at different stages of the content distribution process, ranging from the establishment of initial keying information before transmission, to key management while delivering through networks, and finally to content protection and collusion prevention/tracing after delivery. We address the issue of establishing a group key prior to content delivery by introducing the butterfly scheme and a conference keying scheme that addresses user heterogeneity. These schemes employ the two-party Diffie-Hellman scheme in conjunction with an underlying algorithmic tree called the conference tree. In order to address client heterogeneity, we design the conference tree using source coding techniques to account for the different user cost and budget profiles. We also introduce the PESKY performance measure, which quantifies the likelihood that a conference key can be established in a heterogeneous environment. We then consider the problem of managing keys during content delivery by proposing a multicast key management system that uses a composite message format with member join and departure operations. Compared with the traditional format of the rekeying messages used in tree-based multicast key management, our composite message format reduces the amount of header information, while maintaining the same payload size. Finally, we address the issue of protecting the digital rights of multimedia content after it has left the protected or encrypted domain. Since traditional multimedia fingerprints are susceptible to collusion attacks made by a coalition of adversaries, we develop fingerprints for multimedia that are based upon code modulation and able to identify groups of colluders.
ON ROUTING AND PERFORMANCE EVALUATION OF BUFFERED SPARSE CROSSBAR CONCENTRATORS
(2002-12-10) Ratan, Rahul; Oruc, A. Yavuz; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD.)
We investigate the routing and performance of sparse crossbar packet concentrators under a buffered network model. The concentration property in packet switching concentrators is defined with respect to packets instead of input/output ports. This allows such concentrators to function as generalized connectors (with some constraints). This altered functionality for a packet concentrator over its circuit switched counterpart translates into differences in performance measures like complexity and delay. A model for constructing sparse crossbar packet switching concentrators with optimal cross point complexity has been introduced in literature. We use this construction to model the performance of a sparse crossbar packet concentrator and relate performance measures to its complexity, connectivity and buffer requirements. In this thesis, we address issues of routing and performance evaluation over such optimal sparse crossbar fabrics, in particular their relation to complexity and buffer requirements. We present an analysis of the packet loss suffered in such concentrators when excess packets are dropped. We go on to analyze the best performance possible when packets are stored and serviced in FIFO order. These results lead us to formulate a routing algorithm which tries to emulate the best case performance on the sparse crossbar. We present theoretical and simulation results for the best case performance and the algorithm. We find that the algorithm is efficient and allows concentration to be done with negligible loss of performance on the sparse crossbar.
Indium Phosphide Based Optical Micro-Ring Resonators
(2003-10-24) Grover, Rohit; Ho, Ping-Tong; Goldhar, Julius; Ghodssi, Reza; Ritter, Kenneth J; Electrical Engineering
Micro-ring resonators are a strong candidate for the basic building blocks of very-large-scale-integrated optics. They can be used in many applications, such as filters, routers, switches, lasers, and amplifiers. They are simple in design and concept, can be made very small, and do not require exotic materials or fabrication techniques. In this thesis, I describe my work on indium phosphide based active and passive micro-ring resonators. To enable low-loss devices, I develop a dry-etching process for InP using the methane chemistry in a capacitively-coupled reactive-ion-etching machine. Using the etch process, I demonstrate single-mode micro-ring resonators in the vertically- and laterally-coupled geometries, all-optical logic, and a tunable micro-ring notch filter. The best devices in the vertically-coupled geometry have bandwidth as low as $0.24~\nm$, free spectral range of $24~\nm$, $Q = 6200$, and finesse of $100$ while the laterally-coupled micro-rings have bandwidth as low as $0.25~\nm$, free spectral range of $8~\nm$, $Q = 6250$, and finesse of $32$. Some of the laterally-coupled devices have free spectral ranges as high as $28~\nm$, though the corresponding $Q$ is low. Tarek Ibrahim and I demonstrate all-optical logic (AND operation) using carrier-induced refractive index change by two-photon-absorption with switching speed of $100~\ps$, dominated by ambipolar diffusion. Finally, I demonstrate tuning by $100~\GHz$ ($0.8~\nm$) with $8~\volt$ reverse bias of an InP-based micro-ring resonator with a p-i-n structure using the quadratic electro-optic effect, obtaining $1.5~\GHz/\volt^2$ of tuning.
Nonlinear Optical Semiconductor Micro-Ring Resonators
(2003-11-05) Ibrahim, Tarek Adly; Goldhar, Julius; Ho, Ping-Tong; Lee, Chi H; Hill, Wendell T; Electrical Engineering
In the last few years, there has been a great interest in all-optical switching devices due to the high demand on optical communication systems and networks. Unlike conventional electronic switches, photonic switching devices are ideal candidates for ultrafast data stream processing, approaching the THz regime. It is the goal of this thesis to propose, study, and demonstrate a new class of compact optical switches based on semiconductor microring resonators. A detailed theoretical analysis of the nonlinear behavior of the microring resonator shows that, due to the resonance effect, there is an enhancement of the overall switching efficiency by up to the third power of the cavity finesse. Two different semiconductor materials are used in fabricating these devices, GaAs and InP. Both materials are analyzed and compared in terms of switching energy requirement, nonlinear coefficients, speed limitation and ease of fabrication. In addition, two different fabrications techniques are used to realize the ring structure layout, laterally and vertically coupled. The round trip phase of the microring resonator can be controlled by changing its refractive index. This can be accomplished by free carrier injection induced by two-photon absorption or single-photon absorption. As a result, a temporal blue shift in the resonator resonance wavelength is observed. When these carriers diffuse to the waveguide walls, the effect diminishes. A probe beam, tuned to one of the resonator resonant wavelengths, is used to capture the dynamic change in the transmission function of the resonator. All-optical switching is demonstrated using a single microring resonator, with few tens of picojoules switching energy and a switching window approaching 30 GHz, limited by the carrier lifetime of the guiding material. Moreover, such a device is used in time division demultiplexing a stream of data channels as well as spatial pulse routing with approximately 8~dB cross-talk noise, limited by fabrication tolerances. More complicated structures of these resonators are proposed and used to achieve a set of functionally complete photonic logic gates.
Algorithms for Gait-Based Human Identification from a Monocular Video Sequence
(2003-11-12) Kale, Amit A; Chellappa, Rama; Electrical Engineering
Human gait is a spatio-temporal phenomenon that characterizes the motion characteristics of an individual. It is possible to detect and measure gait even in low-resolution video. This makes it an attractive modality in surveillance applications, where it is often difficult to get face or iris information at high enough resolution for recognition applications. Psychophysical studies indicate that humans have the capability for recognizing people from even impoverished displays of gait, indicating the presence of identity information. From early medical studies it appears that there are twenty four different components to human gait, and that if all the measurements are considered, gait is unique. It is interesting, therefore, to study the utility of gait as a biometric. The goal of this thesis is to investigate the information contained in the video sequences of human gait and how to extract and exploit that information in ways that facilitate human identification. In our work, we present both deterministic and stochastic approaches for gait recognition. Human identification using gait, similar to text-based speaker identification, involves different individuals performing the same task and a template-matching approach is suitable for such problems. In situations where the amount of training data is limited, we show the utility of a simple feature viz. the width of the outer contour of the binarized silhouette of the subject and its derivatives for gait recognition in a dynamic time warping framework. By virtue of their deterministic nature, template matching methods have limited noise resilience. A careful analysis of gait would reveal that it has two important components. The first is a structural component that captures the physical build of a person while the second is the motion kinematics of the body during a gait cycle. We propose a systematic approach to gait recognition by building representations for the structural and dynamic components of gait using exemplars and hidden Markov models (HMMs). The stochastic nature of the HMM yields better noise resilience than the template matching technique. To recognize a person walking at a large distance, humans try to combine information such as posture, arm/leg swing, hip/upper body sway or some unique movements that are characteristic of that person. We demonstrate the same effect through fusion of different dynamic and static gait features in both determinisitic and stochastic frameworks. Most gait recognition algorithms rely on the availability of an exact side view in the probe. However, it is not realistic to expect that this assumption will be valid in most real-life scenarios. We present a view invariant gait recognition algorithm which is based on synthesizing a side view of a person from an arbitrary monocular view. The method is based on the planar approximation of a person that is valid when human identification at a distance is desired.
An Optimization Theoretical Framework for Resource Allocation over Wireless Networks
(2003-11-24) Han, Zhu; Liu, K.J. Ray; Electrical Engineering
With the advancement of wireless technologies, wireless networking has become ubiquitous owing to the great demand of pervasive mobile applications. Some fundamental challenges exist for the next generation wireless network design such as time varying nature of wireless channels, co-channel interferences, provisioning of heterogeneous type of services, etc. So how to overcome these difficulties and improve the system performance have become an important research topic. Dynamic resource allocation is a general strategy to control the interferences and enhance the performance of wireless networks. The basic idea behind dynamic resource allocation is to utilize the channel more efficiently by sharing the spectrum and reducing interference through optimizing parameters such as the transmitting power, symbol transmission rate, modulation scheme, coding scheme, bandwidth, etc. Moreover, the network performance can be further improved by introducing diversity, such as multiuser, time, frequency, and space diversity. In addition, cross layer approach for resource allocation can provide advantages such as low overhead, more efficiency, and direct end-to-end QoS provision. The designers for next generation wireless networks face the common problem of how to optimize the system objective under the user Quality of Service (QoS) constraint. There is a need of unified but general optimization framework for resource allocation to allow taking into account a diverse set of objective functions with various QoS requirements, while considering all kinds of diversity and cross layer approach. We propose an optimization theoretical framework for resource allocation and apply these ideas to different network situations such as: 1.Centralized resource allocation with fairness constraint 2.Distributed resource allocation using game theory 3.OFDMA resource allocation 4.Cross layer approach On the whole, we develop a universal view of the whole wireless networks from multiple dimensions: time, frequency, space, user, and layers. We develop some schemes to fully utilize the resources. The success of the proposed research will significantly improve the way how to design and analyze resource allocation over wireless networks. In addition, the cross-layer optimization nature of the problem provides an innovative insight into vertical integration of wireless networks.
HIGH-IMPEDANCE ELECTROMAGNETIC SURFACES FOR MITIGATION OF SWITCHING NOISE IN HIGH-SPEED CIRCUITS
(2003-11-24) Kamgaing, Telesphor; Ramahi, Omar M.; Granatstein, Victor; Mayergoyz, Isaak; Newcomb, Robert; Electrical Engineering
With the increasing gate density, the rising clock frequency, printed circuit board (PCB) level simultaneous switching noise (SSN) has become a major bottleneck for the signal integrity in high-speed microprocessors and computers. All approaches that are currently being used to address this problem have been proven inefficient for switching frequencies of 500 MHz and above. The research work carried out in this dissertation addresses a novel technique for mitigating high-frequency SSN by suppressing the natural parallel-plate resonant modes encountered in traditional power planes. This is done by replacing at least one of the power planes of the power distribution network with a high-impedance electromagnetic surface (HIS). The high-impedance electromagnetic surface, which indeed is an artificial magnetic conductor, prevents any surface wave propagation in its forbidden band-gap, therefore leading to the suppression of resonant modes. Using full wave electromagnetic simulation and experimental verification, the fundamental limitations of SSN mitigation using standard HIS is investigated. It is found that the thickness of the dielectric substrate and the metal line spacing offered by most PCB technologies are fundamental limitations for achieving broadband simultaneous switching noise mitigation at frequencies below 3 GHz for high-density packaging. This restriction is addressed by developing a new family of HIS, whose surface impedance is mainly controlled by the inductance density. These novel inductively-tuned HIS offer the possibility of mitigating switching noise at frequencies of 1 GHz and below frequencies and can be fabricated using conventional PCB technology. It is also demonstrated that the combination of these novel HIS with RC dissipative edge termination (DET) leads to broadband simultaneous switching noise mitigation from DC to about 3 or 4 GHz. Finally physics-based compact models that allow the use of the novel power planes with other components for full package simulation are developed and validated for power planes with integrated standard and double-layer HIS. These models utilize only frequency independent lumped-components and are, therefore, particularly attractive for transient analysis.