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<p> Telemedicine traffic transmission over wireless cellular networks has gained in importance during the last few years. Most of the current research in the field has focused on software and hardware implementations for telemedicine transmission, without discussing the case of simultaneous transmission of both urgent telemedicine traffic and regular multimedia traffic over the network.</p> <p> Due to the fact that telemedicine traffic carries critical information regarding the patients' condition, it is vitally important that this traffic has highest transmission priority in comparison to all other types of traffic in the cellular network. However, the need for expedited and correct transmission of telemedicine traffic calls for a guaranteed bandwidth to telemedicine users. This creates a tradeoff between the satisfaction of the very strict Quality of Service (QoS) requirements of telemedicine traffic and the loss of the guaranteed bandwidth in the numerous cases when it is left unused, due to the infrequent nature of telemedicine traffic. This waste of the bandwidth may lead to a lack of sufficient bandwidth for regular traffic, hence degrading its QoS.</p> <p> To resolve this complex problem, in this thesis, we propose a) an adaptive bandwidth reservation scheme based on road map information and on users' mobility, and b) a fair scheduling scheme for video traffic transmission over wireless cellular networks. The proposed combination of the two schemes, which is evaluated over a hexagonal cellular structure, is shown to achieve high channel bandwidth utilization while offering full priority to telemedicine traffic.</p> / Thesis / Master of Applied Science (MASc)

No / Effective media server placement strategies are critical for the quality and cost of multimedia services. Existing studies have primarily focused on optimization-based algorithms to select server locations from a small pool of candidates based on the entire topological information and thus these algorithms are not scalable due to unavailability of the small pool of candidates and low-efficiency of gathering the topological information in large-scale networks. To overcome this limitation, a novel scalable framework called NetClust is proposed in this paper. NetClust takes advantage of the latest network coordinate technique to reduce the workloads when obtaining the global network information for server placement, adopts a new Kappa -means-clustering-based algorithm to select server locations and identify the optimal matching between clients and servers. The key contribution of this paper is that the proposed framework optimizes the trade-off between the service delay performance and the deployment cost under the constraints of client location distribution and the computing/storage/bandwidth capacity of each server simultaneously. To evaluate the performance of the proposed framework, a prototype system is developed and deployed in a real-world large-scale Internet. Experimental results demonstrate that 1) NetClust achieves the lower deployment cost and lower delay compared to the traditional server selection method; and 2) NetClust offers a practical and feasible solution for multimedia service providers.

This research solves current RF propagation modeling gaps by modifying a single-frequency electromagnetic propagation analysis technique for use on communication signals and propagation channels. This research extended the Methods of Ordered Multiple Interactions (MOMI) algorithm to communication signal propagation studies through the use of Fourier decomposition thereby allowing the analysis and prediction of communication signals propagating over rough surfaces. Current methods of predicting and analyzing communication signal propagation rely on either using only a single frequency instead of a band of frequencies, stochastic techniques that model the environmental effect on the propagated signal, or on empirical models based of large amounts of measured situational data. None of these methods fully capture the actual effect that an environment imparts on a communication signal as it propagates. This research also modifies the Physical Optics (PO) algorithm utilizing Fourier decomposition to compare the Extended MOMI algorithm to. Both algorithms are applied to propagation scenarios utilizing frequencies in the 1-GHz and 5-GHz bands against a series of signal bandwidths and surface roughnesses. The results are analyzed singularly for Extended-MOMI and against Extended-Physical Optics to better understand the benefits associated with using the Extended-MOMI, the limits of the narrowband approximation, the errors incurred when utilizing a simpler or faster propagation algorithm, and to generally characterize these rough surface propagation channels. This research also defines and explores which metrics provide the best characterization and utility for communication signal propagation with the additional insights of amplitude-frequency-phase relationships the new algorithm provides. / Doctor of Philosophy / Communication signal propagation, defined as the propagation of signals that have non-zero bandwidths from one point to another, has significant importance in communication signal design, system design, and deployment as well as in spectrum planning applications. Current methods of predicting and analyzing communication signal propagation rely on either using only a single frequency instead of a band of frequencies, stochastic techniques that model the environmental effect on the propagated signal, or on empirical models based of large amounts of measured situational data. None of these methods fully capture the actual effect that an environment imparts on a communication signal as it propagates. A technique that accurately models the environmental effect on propagating communication signals would result in knowledge about a communication signal strength and shape as it passes through the propagation space. Analyzing communication signals with single frequency propagation algorithms requires assuming all the frequencies that make up the communication signal propagate exactly the same way, an assumption known as the narrowband approximation. It is not known when the narrowband approximation breaks down in various circumstances. Consequently a more rigorous approach needed to be identified to enable a more accurate and complete analysis of communication signals, which is the objective of the research. This research solves these modeling gaps by modifying a single-frequency electromagnetic propagation analysis technique, the Method of Ordered Multiple Interactions, for use on communication signals and propagation channels. The new algorithm, Extended-MOMI, allows for an examination of communication signal propagation over rough surfaces. This new algorithm incorporates all of the information needed for communication signal propagation analysis; something that is missing from current methods. This technique enables tailored communication signal propagation studies as well as an investigations into when the narrowband assumption is valid and when simpler and faster algorithms could be utilized for a now known increase in error. This research also explores which metrics are best utilized with the additional signal information the new algorithm enables.

Yes / This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC) and capacity loss. These characteristics indicate that the proposed antenna suitable for some wireless applications.

No / This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm 2 . It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC) and capacity loss. These characteristics indicate that the proposed antenna suitable for some wireless applications. Mutual Coupling Reduction of Two Elements Antenna for Wireless Applications. Available from: https://www.researchgate.net/publication/261064207_Mutual_Coupling_Reduction_of_Two_Elements_Antenna_for_Wireless_Applications [accessed Aug 1, 2017].

Advances in transistor-integration technology and multi-core technology of the latest microprocessors have driven transient requirements to become more and more stringent. Rather than relying on the bulky output capacitors as energy-storage devices, increasing the control bandwidth (BW) of the multiphase voltage regulator (VR) is a more cost-effective and space-saving approach. However, it is found that the stability margin of current-mode control in high-BW design is very sensitive to operating conditions and component tolerance, depending on the performance of the current-sensing techniques, modulation schemes, and interleaving approaches. The primary objective of this dissertation is to investigate an advanced multiphase current-mode control, which provides accurate current sensing, enhances the stability margin in high-BW design, and adaptively compensates the parameter variations. Firstly, an equivalent circuit model for generic current-mode controls using DCR current sensing is developed to analyze the impact of component tolerance in high-BW design. Then, the existing state-of-the-art auto-tuning method used to improve current-sensing accuracy is reviewed, and the deficiency of using this method in a multiphase VR is identified. After that, enlightened by the proposed model, a novel auto-tuning method is proposed. This novel method features better tuning performance, noise-insensitivity, and simpler implementation than the state-of-the-art method. Secondly, the current state-of-the-art adaptive current-mode control based on constant-frequency PWM is reviewed, and its inability to maintain adequate stability margin in high-BW design is recognized. Therefore, a new external ramp compensation technique is proposed to keep the stability margin insensitive to the operating conditions and component tolerance, so the proposed high-BW constant-frequency control can meet the transient requirement without the presence of bulky output capacitors. The control scheme is generic and can be used in various kinds of constant-frequency controls, such as peak-current-mode, valley-current-mode, and average-current-mode configurations. Thirdly, an interleaving technique incorporating an adaptive PLL loop is presented, which enables the variable-frequency control to push the BW higher than proposed constant-frequency control, and avoids the beat-frequency input ripple. A generic small-signal model of the PLL loop is derived to investigate the stability issue caused by the parameter variations. Then, based on the proposed model, a simple adaptive control is developed to allow the BW of the PLL loop to be anchored at the highest phase margin. The adaptive PLL structure is applicable to different types of variable-frequency control, including constant on-time control and ramp pulse modulation. Fourthly, a hybrid interleaving structure is explored to simplify the implementation of the adaptive PLL structure in an application with more phases. It combines the adaptive PLL loop with a pulse-distribution technique to take the advantage of the high-BW design and fast transient response without adding a burden to the controller implementation. As a conclusion, based on the proposed analytical models, effective control concepts, systematic optimization strategies, viable implementations are fully investigated for high-BW current-mode control using different modulation techniques. Moreover, all the modeling results and the system performance are verified through simulation with a practical output filter model and an advanced mixed-signal experimental platform based on the latest MHz VR design on the laptop motherboard. In consequence, the multiphase VRs in future computation systems can be scalable easier with proposed multiphase configurations, increase the system reliability with proposed adaptive loop compensation, and minimize the total system footprint of the VR with the superior transient performance. / Ph. D.

Recently there has been a significant amount of interest in the area of wideband and ultra-wideband (UWB) signaling for use in indoor wireless systems. This interest is in part motivated by the notion that the use of large bandwidth signals makes systems less sensitive to the degrading effects of multipath propagation. By reducing the sensitivity to multipath, more robust and higher capacity systems can be realized. However, as signal bandwidth is increased, the complexity of a Rake receiver (or other receiver structure) required to capture the available power also increases. In addition, accurate channel estimation is required to realize this performance, which becomes increasingly difficult as energy is dispersed among more multipath components. In this thesis we quantify the channel response for six signal bandwidths ranging from continuous wave (CW) to 1 GHz transmission bandwidths. We present large scale and small scale fading statistics for both LOS and NLOS indoor channels based on an indoor measurement campaign conducted in Durham Hall at Virginia Tech. Using newly developed antenna positioning equipment we also quantify the spatial correlation of these signals. It is shown that the incremental performance gains due to reduced fading of large bandwidths level off as signals approach UWB bandwidths. Furthermore, we analyze the performance of Rake receivers for the different signal bandwidths and compare their performance for binary phase modulation (BPSK). It is shown that the receiver structure and performance is critical in realizing the reduced fading benefit of large signal bandwidths. We show practical channel estimation degrades performance more for larger bandwidths. We also demonstrate for a fixed finger Rake receiver there is an optimal signal bandwidth beyond which increased signal bandwidth produces degrading results. / Master of Science