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(1 - 7 of 7)
- Title
- DATA TRANSMISSION SCHEDULING FOR DISTRIBUTED SIMULATION USING PACKET ALLOYING.
- Creator
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Vargas-Morales, Juan, DeMara, Ronald, University of Central Florida
- Abstract / Description
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Communication bandwidth and latency reduction techniques are developed for Distributed Interactive Simulation (DIS) protocols. Using logs from vignettes simulated by the OneSAF Testbed Baseline (OTB), a discrete event simulator based on the OMNeT++ modeling environment is developed to analyze the Protocol Data Unit (PDU) traffic over a wireless flying Local Area Network (LAN). Alternative PDU bundling and compression techniques are studied under various metrics including slack time, travel...
Show moreCommunication bandwidth and latency reduction techniques are developed for Distributed Interactive Simulation (DIS) protocols. Using logs from vignettes simulated by the OneSAF Testbed Baseline (OTB), a discrete event simulator based on the OMNeT++ modeling environment is developed to analyze the Protocol Data Unit (PDU) traffic over a wireless flying Local Area Network (LAN). Alternative PDU bundling and compression techniques are studied under various metrics including slack time, travel time, queue length, and collision rate. Based on these results, Packet Alloying, a technique for the optimized bundling of packets, is proposed and evaluated. Packet Alloying becomes more active when it is needed most: during negative spikes of transmission slack time. It produces aggregations that preserve the internal PDU format, allowing the resulting packets to be subjectable to further bundling and/or compression by conventional techniques. To optimize the selection of bundle delimitation, three online predictive strategies were developed: Neural-Network based, Always-Wait, and Always-Send. These were compared with three offline strategies defined as Type, Type-Length and Type-Length-Size. Applying Always-Wait to the studied vignette using the wireless links set to 64 Kbps, a reduction in the magnitude of negative slack time from -75 to -9 seconds for the worst spike was achieved, which represents a reduction of 88 %. Similarly, at 64 Kbps, Always-Wait reduced the average satellite queue length from 2,963 to 327 messages for a 89% reduction. From the analysis of negative slack-time spikes it was determined which PDU types are of highest priority. The router and satellite queues in the case study were modified accordingly using a priority-based transmission scheduler. The analysis of total travel times based of PDU types numerically shows the benefit obtained. The contributions of this dissertation include the formalization of a selective PDU bundling scheme, the proposal and study of different predictive algorithms for the next PDU, and priority-based optimization using Head-of-Line (HoL) service. These results demonstrate the validity of packet optimizations for distributed simulation environments and other possible applications such as TCP/IP transmissions.
Show less - Date Issued
- 2004
- Identifier
- CFE0000302, ucf:46312
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000302
- Title
- Enhancement of Bandwidth and Laser Deflection Angle of Acousto-optic Deflectors by Dynamic Two-dimensional Refractive Index Modulation.
- Creator
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Wang, Tiansi, Kar, Aravinda, Likamwa, Patrick, Moharam, Jim, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
-
Acousto-Optic Deflectors (AODs) are inertialess optical solid state devices that have advantages over conventional mechanically controlled mirror-based deflectors in numerous scientific and industrial applications. These applications include fluorescence microscopy, sensing, variable-focus lens, photolithography and laser materials processing. AODs are currently operated with a single piezoelectric transducer that modulates the refractive index only in one direction. This operating principle...
Show moreAcousto-Optic Deflectors (AODs) are inertialess optical solid state devices that have advantages over conventional mechanically controlled mirror-based deflectors in numerous scientific and industrial applications. These applications include fluorescence microscopy, sensing, variable-focus lens, photolithography and laser materials processing. AODs are currently operated with a single piezoelectric transducer that modulates the refractive index only in one direction. This operating principle limits the performance of AODs to a narrow acoustic bandwidth of the transducer and a small angle of laser deflection governed by the Bragg diffraction. To overcome these two limitations, the operation of AODs with phased array ultrasonic transducers is analyzed in this study. Only the amplitude and frequency of the acoustic waves are modulated in conventional AODs. The phased array mechanism enables modulating the acoustic phase in addition to the amplitude and frequency modulations. The latter two phenomena affect the refractive index variation and its periodicity in the AOD medium, respectively, and the phase modulation produces tilted wavefronts due to diffraction and interference of the ultrasonic waves. Consequently, a tilted phase grating is formed inside the AOD device and the tilt angle automatically modifies the laser incident angle on the grating compared to the original angle of incidence on the AOD device. The acoustic frequency and amplitude are, therefore, modulated to achieve the Bragg diffraction under the new angle of incidence and maximize the diffraction efficiency, respectively. The phase grating can be tilted at any arbitrary angle by steering the ultrasonic beam in different directions. The beam steering can be achieved by operating the transducers with various time delays to generate ultrasonic waves of different phases. Due to the diffraction pattern of the ultrasonic intensity distribution, the refractive index varies both longitudinally and transversely to the beam steering direction, and two-dimensional refractive index modulation occurs when the transducers are very long in the third dimension. The acoustic waves affect the refractive index through the photoelastic effect by inducing mechanical strain waves in the AOD medium. The ultrasonic beam steering and the mechanical strain are determined using a modified Rayleigh-Sommerfeld diffraction integral. This integral represents the mechanical displacement vector field produced by ultrasonic waves in solid media. An analytic expression is obtained for the displacement field and the resulting strain distribution is calculated using this expression. Based on the strain and the photoelastic constants, the two-dimensional variation in the refractive index is determined for single-crystal paratellurite TeO2 which is an excellent AOD material. Conventional two-dimensional coupled mode theory of AOD, which is based on only one-dimensional refractive index modulation, is extended in this study to analyze the effect of two-dimensional index variation on the performance of AODs. The diffraction efficiency and the laser beam deflection angle are determined for both plane waves and Gaussian laser beams by obtaining analytic solutions for the coupled mode equations. The diffraction efficiency is found to be nearly unity over a broad range of the acoustic frequency, and the deflection angle can also be increased by steering the ultrasonic beam at large angles.
Show less - Date Issued
- 2017
- Identifier
- CFE0006672, ucf:51219
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006672
- Title
- CONTROL AND TOPOLOGY IMPROVEMENTS IN HALF-BRIDGE DC-DC CONVERTERS.
- Creator
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Deng, Songquan, Batarseh, Issa, University of Central Florida
- Abstract / Description
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Efficiency and transient response are two key requirements for DC-DC converters. Topology and control are two key topics in this dissertation. A variety of techniques for DC-DC converter performance improvement are presented in this work. Focusing on the efficiency issue, a variety of clamping techniques including both active and passive methods are presented after the ringing issues in DC-DC converters are investigated. By presenting the clamping techniques, a big variety of energy...
Show moreEfficiency and transient response are two key requirements for DC-DC converters. Topology and control are two key topics in this dissertation. A variety of techniques for DC-DC converter performance improvement are presented in this work. Focusing on the efficiency issue, a variety of clamping techniques including both active and passive methods are presented after the ringing issues in DC-DC converters are investigated. By presenting the clamping techniques, a big variety of energy management concepts are introduced. The active bridge-capacitor tank clamping and FET-diode-capacitor tank clamping are close ideas, which transfer the leakage inductor energy to clamping capacitor to prevent oscillation between leakage inductor and junction capacitor of MOSFETs. The two-FET-clamping tank employs two MOSFETs to freewheeling the leakage current when the main MOSFETs of the half-bridge are both off. Driving voltage variation on the secondary side Synchronous Rectifier (SR) MOSFETs in self-driven circuit due to input voltage variation in bus converter applications is also investigated. One solution with a variety of derivations is proposed using zerner-capacitor combination to clamping the voltage while maintaining reasonable power losses. Another efficiency improvement idea comes from phase-shift concept in DC-DC converters. By employing phase-shift scheme, the primary side and the secondary side two MOSFETs have complementary driving signals respectively, which allow the MOSFET to be turned on with Zero Voltage Switching (ZVS). Simulation verified the feasibility of the proposed phase-shifted DC-DC converter. From the control scheme point of view, a novel peak current mode control concept for half-bridge topologies is presented. Aiming at compensating the imbalanced voltage due to peak current mode control in symmetric half-bridge topologies, an additional voltage compensation loop is used to bring the half-bridge capacitor voltage back to balance. In the proposed solutions, one scheme is applied on symmetric half-bridge topology and the other one is applied on Duty-cycle-shifted (DCS) half-bridge topology. Both schemes employ simple circuitry and are suitable for integration. Loop stability issues are also investigated in this work. Modeling work shows the uncompensated half-bridge topology cannot be stabilized under all conditions and the additional compensation loop helps to prevent the voltage imbalance effectively.
Show less - Date Issued
- 2005
- Identifier
- CFE0000840, ucf:46674
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000840
- Title
- The Performance and Power Impact of Using Multiple DRAM Address Mapping Schemes in Multicore Processors.
- Creator
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Jadaa, Rami, Heinrich, Mark, DeMara, Ronald, Yuan, Jiann-Shiun, University of Central Florida
- Abstract / Description
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Lowest-level cache misses are satisfied by the main memory through a specific address mapping scheme that is hard-coded in the memory controller. A dynamic address mapping scheme technique is investigated to provide higher performance and lower power consumption, and a method to throttle memory to meet a specific power budget. Several experiments are conducted on single and multithreaded synthetic memory traces -to study extreme cases- and validate the usability of the proposed dynamic...
Show moreLowest-level cache misses are satisfied by the main memory through a specific address mapping scheme that is hard-coded in the memory controller. A dynamic address mapping scheme technique is investigated to provide higher performance and lower power consumption, and a method to throttle memory to meet a specific power budget. Several experiments are conducted on single and multithreaded synthetic memory traces -to study extreme cases- and validate the usability of the proposed dynamic mapping scheme over the fixed one. Results show that applications' performance varies according to the mapping scheme used, and a dynamic mapping scheme achieves up to 2x increase in peak bandwidth utilization and around 30% higher energy efficiency than a system using only a single fixed scheme Moreover, the technique can be used to limit memory accesses into a subset of the memory devices by controlling data allocation at a finer granularity, providing a method to throttle main memory by allowing un-accessed devices to be put into power-down mode, hence saving power to meet a certain power budget.
Show less - Date Issued
- 2011
- Identifier
- CFE0004121, ucf:49118
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004121
- Title
- A Study of Internet Spending and Graduation Rates: A Correlational Study.
- Creator
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Violette, Diana, Murray, Kenneth, Baldwin, Lee, Doherty, Walter, Jaffe, Larry, University of Central Florida
- Abstract / Description
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The purpose of this study was to examine the relationship between school district spending on Internet access and student achievement, defined by graduation rates, in the state of Florida. Internet funding received for Internet access from E-rate funding administered by the Universal Service Administration Company (USAC) and graduation rates of the 67 school districts in the state of Florida were compared. Further, the data were adjusted for socio-economic status (SES) to determine the...
Show moreThe purpose of this study was to examine the relationship between school district spending on Internet access and student achievement, defined by graduation rates, in the state of Florida. Internet funding received for Internet access from E-rate funding administered by the Universal Service Administration Company (USAC) and graduation rates of the 67 school districts in the state of Florida were compared. Further, the data were adjusted for socio-economic status (SES) to determine the relationship between school districts' SES and spending on Internet access. Lastly, school district connectivity and bandwidth were examined to determine whether the ConnectED initiative requirements were related to student achievement and the implementation of school district digital learning programs. E-rate funding and graduation rates were not correlated. Regression and multiple regression analyses demonstrated that Internet spending, bandwidth, and ratio of computers to students did not statistically predict graduation rates during the years of the study.
Show less - Date Issued
- 2017
- Identifier
- CFE0006816, ucf:51771
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006816
- Title
- Broad Bandwidth, All-fiber, Thulium-doped Photonic Crystal Fiber Amplifier for Potential Use in Scaling Ultrashort Pulse Peak Powers.
- Creator
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Sincore, Alex, Richardson, Martin, Shah, Lawrence, Amezcua Correa, Rodrigo, University of Central Florida
- Abstract / Description
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Fiber based ultrashort pulse laser sources are desirable for many applications; however generating high peak powers in fiber lasers is primarily limited by the onset of nonlinear effects such as self-phase modulation, stimulated Raman scattering, and self-focusing. Increasing the fiber core diameter mitigates the onset of these nonlinear effects, but also allows unwanted higher-order transverse spatial modes to propagate. Both large core diameters and single-mode propagation can be...
Show moreFiber based ultrashort pulse laser sources are desirable for many applications; however generating high peak powers in fiber lasers is primarily limited by the onset of nonlinear effects such as self-phase modulation, stimulated Raman scattering, and self-focusing. Increasing the fiber core diameter mitigates the onset of these nonlinear effects, but also allows unwanted higher-order transverse spatial modes to propagate. Both large core diameters and single-mode propagation can be simultaneously attained using photonic crystal fibers.Thulium-doped fiber lasers are attractive for high peak power ultrashort pulse systems. They offer a broad gain bandwidth, capable of amplifying sub-100 femtosecond pulses. The longer center wavelength at 2 ?m theoretically enables higher peak powers relative to 1 ?m systems since nonlinear effects inversely scale with wavelength. Also, the 2 ?m emission is desirable to support applications reaching further into the mid-IR.This work evaluates the performance of a novel all-fiber pump combiner that incorporates a thulium-doped photonic crystal fiber. This fully integrated amplifier is characterized and possesses a large gain bandwidth, essentially single-mode propagation, and high degree of polarization. This innovative all-fiber, thulium-doped photonic crystal fiber amplifier has great potential for enabling high peak powers in 2 ?m fiber systems; however the current optical-to-optical efficiency is low relative to similar free-space amplifiers. Further development and device optimization will lead to higher efficiencies and improved performance.
Show less - Date Issued
- 2014
- Identifier
- CFE0005260, ucf:50611
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005260
- Title
- On Distributed Estimation for Resource Constrained Wireless Sensor Networks.
- Creator
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Sani, Alireza, Vosoughi, Azadeh, Rahnavard, Nazanin, Wei, Lei, Atia, George, Chatterjee, Mainak, University of Central Florida
- Abstract / Description
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We study Distributed Estimation (DES) problem, where several agents observe a noisy version of an underlying unknown physical phenomena (which is not directly observable), and transmit a compressed version of their observations to a Fusion Center (FC), where collective data is fused to reconstruct the unknown. One of the most important applications of Wireless Sensor Networks (WSNs) is performing DES in a field to estimate an unknown signal source. In a WSN battery powered geographically...
Show moreWe study Distributed Estimation (DES) problem, where several agents observe a noisy version of an underlying unknown physical phenomena (which is not directly observable), and transmit a compressed version of their observations to a Fusion Center (FC), where collective data is fused to reconstruct the unknown. One of the most important applications of Wireless Sensor Networks (WSNs) is performing DES in a field to estimate an unknown signal source. In a WSN battery powered geographically distributed tiny sensors are tasked with collecting data from the field. Each sensor locally processes its noisy observation (local processing can include compression,dimension reduction, quantization, etc) and transmits the processed observation over communication channels to the FC, where the received data is used to form a global estimate of the unknown source such that the Mean Square Error (MSE) of the DES is minimized. The accuracy of DES depends on many factors such as intensity of observation noises in sensors, quantization errors in sensors, available power and bandwidth of the network, quality of communication channels between sensors and the FC, and the choice of fusion rule in the FC. Taking into account all of these contributing factors and implementing a DES system which minimizes the MSE and satisfies all constraints is a challenging task. In order to probe into different aspects of this challenging task we identify and formulate the following three problems and address them accordingly:1- Consider an inhomogeneous WSN where the sensors' observations is modeled linear with additive Gaussian noise. The communication channels between sensors and FC are orthogonal power and bandwidth-constrained erroneous wireless fading channels. The unknown to be estimated is a Gaussian vector. Sensors employ uniform multi-bit quantizers and BPSK modulation. Given this setup, we ask: what is the best fusion rule in the FC? what is the best transmit power and quantization rate (measured in bits per sensor) allocation schemes that minimize the MSE? In order to answer these questions, we derive some upper bounds on global MSE and through minimizing those bounds, we propose various resource allocation schemes for the problem, through which we investigate the effect of contributing factors on the MSE.2- Consider an inhomogeneous WSN with an FC which is tasked with estimating a scalar Gaussian unknown. The sensors are equipped with uniform multi-bit quantizers and the communication channels are modeled as Binary Symmetric Channels (BSC). In contrast to former problem the sensors experience independent multiplicative noises (in addition to additive noise). The natural question in this scenario is: how does multiplicative noise affect the DES system performance? how does it affect the resource allocation for sensors, with respect to the case where there is no multiplicative noise? We propose a linear fusion rule in the FC and derive the associated MSE in closed-form. We propose several rate allocation schemes with different levels of complexity which minimize the MSE. Implementing the proposed schemes lets us study the effect of multiplicative noise on DES system performance and its dynamics. We also derive Bayesian Cramer-Rao Lower Bound (BCRLB) and compare the MSE performance of our porposed methods against the bound.As a dual problem we also answer the question: what is the minimum required bandwidth of thenetwork to satisfy a predetermined target MSE?3- Assuming the framework of Bayesian DES of a Gaussian unknown with additive and multiplicative Gaussian noises involved, we answer the following question: Can multiplicative noise improve the DES performance in any case/scenario? the answer is yes, and we call the phenomena as 'enhancement mode' of multiplicative noise. Through deriving different lower bounds, such as BCRLB,Weiss-Weinstein Bound (WWB), Hybrid CRLB (HCRLB), Nayak Bound (NB), Yatarcos Bound (YB) on MSE, we identify and characterize the scenarios that the enhancement happens. We investigate two situations where variance of multiplicative noise is known and unknown. Wealso compare the performance of well-known estimators with the derived bounds, to ensure practicability of the mentioned enhancement modes.
Show less - Date Issued
- 2017
- Identifier
- CFE0006913, ucf:51698
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006913
