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Articles 1 - 30 of 41
Full-Text Articles in Systems and Communications
Integrated Approach To Airborne Laser Communication, James A. Louthain
Integrated Approach To Airborne Laser Communication, James A. Louthain
Theses and Dissertations
Lasers offer tremendous advantages over RF communication systems in bandwidth and security, due to their ultra-high frequency and narrow spatial beamwidth. Atmospheric turbulence causes severe received power variations and high bit error rates (BERs) in airborne laser communication. Airborne optical communication systems require special considerations in size, complexity, power, and weight. Conventional adaptive optics systems correct for the phase only and cannot correct for strong scintillation, but here the two transmission paths are separated sufficiently so that the strong scintillation is \averaged out" by incoherently summing up the two beams in the receiver. This requisite separation distance is derived for …
A Three-Dimensional Pattern-Space Representation For Volumetric Arrays, William C. Barott, Paul G. Steffes
A Three-Dimensional Pattern-Space Representation For Volumetric Arrays, William C. Barott, Paul G. Steffes
Publications
A three-dimensional pattern-space representation is presented for volumetric arrays. In this representation, the radiation pattern of an array is formed by the evaluation of the three-dimensional pattern-space on a spherical surface. The scan angle of the array determines the position of this surface within the pattern-space. This pattern-space representation is used in conjunction with a genetic algorithm to minimize the sidelobe levels exhibited by a thinned volumetric array during scanning.
Collision-Tolerant Transmission With Narrow-Beam Antennas, Hong-Ning Dai, Kam-Wing Ng, Min-You Wu, Bo Li
Collision-Tolerant Transmission With Narrow-Beam Antennas, Hong-Ning Dai, Kam-Wing Ng, Min-You Wu, Bo Li
Hong-Ning Dai
The application of directional antennas in wireless ad hoc networks brings numerous benefits, such as increased spatial reuse and mitigated interference. Most MAC protocols with directional antennas are based on the RTS/CTS mechanism which works well in wireless ad hoc networks using omni-directional antennas. However, RTS/CTS frames cannot mitigate the interference completely. Besides, they also contribute a lot to the performance overhead. This paper studies the problem from a new perspective. We have found that the transmission success probability under directional transmission and directional reception is quite high when the antenna beamwidth is quite narrow. Motivated by the analytical results, …
Effects Of Lline Rate On Vvideo Qos Over Wireless Networks: An Experimental Approach, Stuart Wallace, Mark Davis
Effects Of Lline Rate On Vvideo Qos Over Wireless Networks: An Experimental Approach, Stuart Wallace, Mark Davis
Conference papers
Video streaming over Wireless Local Area Networks (WLANS) is becoming an increasingly popular service. However, end user OoS is highly influenced by many factors. These include the video codec used, the packetization scheme, error concealment and correction techniques, the complexity of the video, propagation losses, and the line rate. In this paper the effect of the line rate on the capacity of the network when streaming multimedia content is analyzed experimentally. It is shown that as the line rate decreases the bandwidth load of the video stream dramatically increases leading to poor QoS at the client side. As automatic line …
Cut Part Count And Increase Dynamic Range In The Hybrid Coupled Attenuator, Chin-Leong Lim
Cut Part Count And Increase Dynamic Range In The Hybrid Coupled Attenuator, Chin-Leong Lim
Chin-Leong Lim
Modern digital modulation formats are generally phase-sensitive. Therefore, the variable attenuators in digital wireless equipment should exhibit minimal phase variation over attenuation. The hybrid coupled attenuator (HCA) has substantially less phase variation than the competing constant-impedance attenuators such as the Pi and the Bridged-T. At microwave frequencies, HCA implementations tend to suffer from reduced dynamic (attenuation) range due to component parasitics, especially when plastic-packaged PIN diodes are selected to lower cost. To maximize the dynamic range in a low-cost 1.9 GHz HCA , we first identified the critical components and then compensated for their deleterious effect. This paper describes the …
Novel Variable Step Size Nlms Algorithms For Echo Cancellation, Mohammad Asif Iqbal, Steven L. Grant
Novel Variable Step Size Nlms Algorithms For Echo Cancellation, Mohammad Asif Iqbal, Steven L. Grant
Electrical and Computer Engineering Faculty Research & Creative Works
In this paper we present two new variable step size (VSS) methods for adaptive filters. These vs.S methods are so effective; they eliminate the need for a separate double-talk detection algorithm in echo cancellation applications. the key feature of both approaches is the introduction of a new near-end signal energy estimator (NE-SEE) that provides accurate and computationally efficient estimates even during double-talk and echo path change events. the first vs.S algorithm applies the NESEE to the recently proposed Nonparametric vs.S NLMS (NPVSS-NLMS) algorithm. the resulting algorithm has excellent convergence characteristics with an intrinsic immunity to double-talk. the second approach is …
Clarifying The Use Of Formative Measurement In The Is Discipline: The Case Of Computer Self-Efficacy, Andrew M. Hardin, Jerry Cha-Jan Chang, Mark A. Fuller
Clarifying The Use Of Formative Measurement In The Is Discipline: The Case Of Computer Self-Efficacy, Andrew M. Hardin, Jerry Cha-Jan Chang, Mark A. Fuller
Management, Entrepreneurship and Technology Faculty Publications
The article offers insights on the use of formative measurement in the information system (IS) discipline. It focuses on the comment which warns researchers on the pitfalls of misapplying formative measures in information system domain as well as on the issues related to computer self-efficacy (CSE) and formative measurement. It then asserts that formative indicator weights are sued in determining the conceptual meaning of constructs and notes that the conceptual definition of CSE will likely differ as they are used in different research models and contexts.
Inhibition Of Linear Absorption In Opaque Materials Using Phase-Locked Harmonic Generation, Marco Centini, Vito Roppo, Eugenio Fazio, Federico Pettazzi, Concita Sibilia, Joseph W. Haus, John V. Foreman, Neset Akozbek, Mark J. Bloemer, Michael Scalora
Inhibition Of Linear Absorption In Opaque Materials Using Phase-Locked Harmonic Generation, Marco Centini, Vito Roppo, Eugenio Fazio, Federico Pettazzi, Concita Sibilia, Joseph W. Haus, John V. Foreman, Neset Akozbek, Mark J. Bloemer, Michael Scalora
Electrical and Computer Engineering Faculty Publications
We theoretically predict and experimentally demonstrate inhibition of linear absorption for phase and group velocity mismatched second- and third-harmonic generation in strongly absorbing materials, GaAs, in particular, at frequencies above the absorption edge.
A 100-fs pump pulse tuned to 1300 nm generates 650 and 435 nm second- and third-harmonic pulses that propagate across a 450−μm-thick GaAs substrate without being absorbed.
We attribute this to a phase-locking mechanism that causes the pump to trap the harmonics and to impress on them its dispersive properties.
Performance Analysis Of Multicarrier Code Division Multiple Access (Mc-Cdma) Systems, Pravinkumar Patil
Performance Analysis Of Multicarrier Code Division Multiple Access (Mc-Cdma) Systems, Pravinkumar Patil
Morehead State Theses and Dissertations
A thesis presented to the faculty of the College of Science and Technology at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Science by Pravinkumar Patil on August 11, 2008.
Architecture For Intelligent Power Systems Management, Optimization, And Storage., J. Chris Foreman
Architecture For Intelligent Power Systems Management, Optimization, And Storage., J. Chris Foreman
Electronic Theses and Dissertations
The management of power and the optimization of systems generating and using power are critical technologies. A new architecture is developed to advance the current state of the art by providing an intelligent and autonomous solution for power systems management. The architecture is two-layered and implements a decentralized approach by defining software objects, similar to software agents, which provide for local optimization of power devices such as power generating, storage, and load devices. These software device objects also provide an interface to a higher level of optimization. This higher level of optimization implements the second layer in a centralized approach …
Design A Pin Diode Switch For High-Linearity Applications, Chin-Leong Lim
Design A Pin Diode Switch For High-Linearity Applications, Chin-Leong Lim
Chin-Leong Lim
This paper describes the semiconductor technology, packaging and characterization of a new PIN diode for switching WCDMA signal up to 10W. PIN semiconductor technology was picked as the basis for this switch because of the various performance and reliability advantages that can be had. A model for the PIN diode is generated based on the measured RF performance. How the various model parameters affect the RF performance is also discussed. This is followed by an application description of a 2.0 GHz switch based on the said model and a discussion of some circuit changes to further improve the performance. The …
A Finite Queue Model Analysis Of Pmrc-Based Wireless Sensor Networks, Qiaoqin Li, Mei Yang, Hongyan Wang, Yingtao Jiang, Jiazhi Zeng
A Finite Queue Model Analysis Of Pmrc-Based Wireless Sensor Networks, Qiaoqin Li, Mei Yang, Hongyan Wang, Yingtao Jiang, Jiazhi Zeng
Electrical & Computer Engineering Faculty Research
In our previous work, a highly scalable and fault- tolerant network architecture, the Progressive Multi-hop Rotational Clustered (PMRC) structure, is proposed for constructing large-scale wireless sensor networks. Further, the overlapped scheme is proposed to solve the bottleneck problem in PMRC-based sensor networks. As buffer space is often scarce in sensor nodes, in this paper, we focus on studying the queuing performance of cluster heads in PMRC-based sensor networks. We develop a finite queuing model to analyze the queuing performance of cluster heads for both non-overlapped and overlapped PMRC-based sensor network. The average queue length and average queue delay of cluster …
The 5 Ghz Airport Surface Area Channel: Part Ii, Measurement And Modeling Results For Small Airports, Indranil Sen, David W. Matolak
The 5 Ghz Airport Surface Area Channel: Part Ii, Measurement And Modeling Results For Small Airports, Indranil Sen, David W. Matolak
Faculty Publications
This paper describes results from a channel measurement campaign performed at several small airports in the U.S. in the 5-GHz band. This paper is a companion to another paper, which describes channel models for large airports. We classify the small airport surface channel into three propagation regions based upon different delay dispersion conditions. The channel characteristics of these regions in the delay and frequency domains are discussed with examples. We provide empirical stochastic channel models (of different bandwidths) to accurately represent the channel on the airport surface area for all propagation regions. The models are provided in the form of …
Rf Applications Of Pin Diodes, Chin-Leong Lim
Rf Applications Of Pin Diodes, Chin-Leong Lim
Chin-Leong Lim
PIN diodes are the ubiquitous "nuts & screws" components that hold together RF equipment as varied as the television, radio, 2-way radios, WLAN equipment etc. This talk covers PIN diode characteristics and RF applications such as switches, attenuators and limiters. Performance improvement techniques will also be discussed.
Significance Of Logic Synthesis In Fpga-Based Design Of Image And Signal Processing Systems, Mariusz Rawski, Henry Selvaraj, Bogdan J. Falkowski, Tadeusz Luba
Significance Of Logic Synthesis In Fpga-Based Design Of Image And Signal Processing Systems, Mariusz Rawski, Henry Selvaraj, Bogdan J. Falkowski, Tadeusz Luba
Electrical & Computer Engineering Faculty Research
This chapter, taking FIR filters as an example, presents the discussion on efficiency of different implementation methodologies of DSP algorithms targeting modern FPGA architectures. Nowadays, programmable technology provides the possibility to implement digital systems with the use of specialized embedded DSP blocks. However, this technology gives the designer the possibility to increase efficiency of designed systems by exploitation of parallelisms of implemented algorithms. Moreover, it is possible to apply special techniques, such as distributed arithmetic (DA). Since in this approach, general-purpose multipliers are replaced by combinational LUT blocks, it is possible to construct digital filters of very high performance. Additionally, …
A Secure And Efficient Communications Architecture For Global Information Grid Users Via Cooperating Space Assets, Victor P. Hubenko
A Secure And Efficient Communications Architecture For Global Information Grid Users Via Cooperating Space Assets, Victor P. Hubenko
Theses and Dissertations
With the Information Age in full and rapid development, users expect to have global, seamless, ubiquitous, secure, and efficient communications capable of providing access to real-time applications and collaboration. The United States Department of Defense’s (DoD) Network-Centric Enterprise Services initiative, along with the notion of pushing the “power to the edge,” aims to provide end-users with maximum situational awareness, a comprehensive view of the battlespace, all within a secure networking environment. Building from previous AFIT research efforts, this research developed a novel security framework architecture to address the lack of efficient and scalable secure multicasting in the low earth orbit …
Vehicle-Vehicle Channel Models For The 5 Ghz Band, Indranil Sen, David W. Matolak
Vehicle-Vehicle Channel Models For The 5 Ghz Band, Indranil Sen, David W. Matolak
Faculty Publications
In this paper, we describe the results of a channel measurement and modeling campaign for the vehicle-to-vehicle (V2V) channel in the 5-GHz band. We describe measurements and results for delay spread, amplitude statistics, and correlations for multiple V2V environments. We also discuss considerations used in developing statistical channel models for these environments and provide some sample results. Several statistical channel models are presented, and using simulation results, we elucidate tradeoffs between model implementation complexity and fidelity. The channel models presented should be useful for system designers in future V2V communication systems.
Channel Modeling For Vehicle-To-Vehicle Communications, David W. Matolak
Channel Modeling For Vehicle-To-Vehicle Communications, David W. Matolak
Faculty Publications
Physical layer channel modeling is critical for design and performance evaluation at multiple layers of the communications protocol stack. In this article we describe and provide results for modeling vehicle-to-vehicle (V2V) wireless channels. V2V settings produce some unique conditions, and due to these conditions, V2V channels often exhibit greater dynamics than many conventional channels and, in addition, can also exhibit more severe fading. Thus, new channel models are needed to characterize this setting in order to evaluate contending transmission schemes and aid in V2V communication system design. A brief review of key statistical channel parameters is provided. Then both analytical …
Spectrally Shaped Generalized Mc-Ds-Cdma With Dual Band Combining For Increased Diversity, Wenhui Xiong, David W. Matolak
Spectrally Shaped Generalized Mc-Ds-Cdma With Dual Band Combining For Increased Diversity, Wenhui Xiong, David W. Matolak
Faculty Publications
A new multicarrier spread spectrum modulation scheme is proposed in this paper. This scheme uses sinusoidal chip waveforms to shape the spectrum of each subcarrier of a multicarrier direct sequence spread spectrum (DS-SS) signal. As a result, each subcarrier has two distinct spectral lobes, one a lower sideband (LSB) and the other an upper sideband (USB). By properly selecting the parameters of the sinusoidal chip waveforms, the two sideband signals can be made to undergo independent fading in a dispersive fading channel. These two independently-faded sideband signals, when combined at the receiver, provide diversity gain to the system. Our analysis …
Analysis Of Mimo Communications Systems Based On Experimentally Observed Channels, Pat Chambers
Analysis Of Mimo Communications Systems Based On Experimentally Observed Channels, Pat Chambers
Doctoral
This thesis presents an analysis of multiple-input/multiple-output (MIMO) communications systems where the objective is to provide a unified solution to the problems of (i) crosstalk coupling in transmission line channels (ii) multi-path fading in the time variant high frequency wireless channel. In the case of transmission line channels, a comparative analysis is presented of the performance of MIMO communications systems based on balanced CAT 5 twisted-pair transmission lines, balanced twisted-pair telephone transmission lines scheme as well as unbalanced flat-pair transmission lines. The unbalanced flat-pair transmission lines are viewed as a model for digital subscriber lines (DSLs) which may be deemed …
Modeling And Characterization Of Adaptive Lanthanum-Modified Lead Zirconate Titanate (Plzt) Microlenses, Yasser A. Abdelaziez, Partha P. Banerjee
Modeling And Characterization Of Adaptive Lanthanum-Modified Lead Zirconate Titanate (Plzt) Microlenses, Yasser A. Abdelaziez, Partha P. Banerjee
Electrical and Computer Engineering Faculty Publications
We report the modeling and characterization of adaptive voltage controlled electro-optic microlenses. First, we utilize finite element analysis (FEA) to simulate the induced electro-optic effect in lanthanum-modified lead zirconate titanate (PLZT). FEA simulation provides microlens parameters such as phase and focal length. A simple z-scan method is developed to fully characterize the adaptive voltage controlled linear lens. Experimental z-scan results are shown to match the theoretical predictions from FEA.
Cut Loss In Low-Voltage, Wideband Pin Attenuators, Chin-Leong Lim
Cut Loss In Low-Voltage, Wideband Pin Attenuators, Chin-Leong Lim
Chin-Leong Lim
Many RF applications, including Cable and Satellite TV (CATV / SATV) networks, rely on voltage-variable attenuators (VVAs) for gain adjustment. VVAs consisting of PIN diodes arranged as a PI network are popular in CATV / SATV service owing to their constant impedance, high linearity, multi-decade bandwidth, low part count and compactness. When fabricated from thick bulk PIN diodes for high linearity, the PI VVA configuration typically requires a 0-15V control range. But modern equipment typically operates at 5V or less. Capping the control voltage at 5V adversely raises the VVA's minimum attenuation. To enable low voltage operation without degrading the …
Tailoring Metallodielectric Structures For Superresolution And Superguiding Applications In The Visible And Near-Ir Ranges, Domenico De Ceglia, Maria Antonietta Vincenti, M. G. Cappeddu, Marco Centini, Neset Akozbek, Antonella D'Orazio, Joseph W. Haus, Mark J. Bloemer, Michael Scalora
Tailoring Metallodielectric Structures For Superresolution And Superguiding Applications In The Visible And Near-Ir Ranges, Domenico De Ceglia, Maria Antonietta Vincenti, M. G. Cappeddu, Marco Centini, Neset Akozbek, Antonella D'Orazio, Joseph W. Haus, Mark J. Bloemer, Michael Scalora
Electrical and Computer Engineering Faculty Publications
We discuss propagation effects in realistic, transparent, metallodielectric photonic band gap structures in the context of negative refraction and super-resolution in the visible and near infrared ranges. In the resonance tunneling regime, we find that for transverse-magnetic incident polarization, field localization effects contribute to a waveguiding phenomenon that makes it possible for the light to remain confined within a small fraction of a wavelength, without any transverse boundaries, due to the suppression of diffraction. This effect is related to negative refraction of the Poynting vector inside each metal layer, balanced by normal refraction inside the adjacent dielectric layer: The degree …
Effects Of Multipath And Oversampling On Navigation Using Orthogonal Frequency Division Multiplexed Signals Of Opportunity, Christopher M. Schexnayder
Effects Of Multipath And Oversampling On Navigation Using Orthogonal Frequency Division Multiplexed Signals Of Opportunity, Christopher M. Schexnayder
Theses and Dissertations
The Global Positioning System (GPS) has become the primary system for navigation and precise positioning. GPS has limitations, though, and is not suitable in environments where a line-of-site (LOS) path to multiple satellites is not available. Reliable alternatives need to be developed to provide GPS-like positioning when GPS is unavailable. One such alternative is to use signals of opportunity (SoOP). This concept refers to navigation using signals which inherently exist in the environment and were developed for non-navigation applications. This research focuses on exploiting the Orthogonal Frequency Division Multiplexed (OFDM) signal for the purpose of navigation. An algorithm was developed …
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Nader Engheta
The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly “invisible” or “transparent” to an outside observer—a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and …
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Andrea Alù
The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly “invisible” or “transparent” to an outside observer—a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and …
Trade-Off Investigation Between Diversity And Spatial Multiplexing In Practical Systems Using Numerical Results, Neda Adib, Hafez Hadinejad Mahram
Trade-Off Investigation Between Diversity And Spatial Multiplexing In Practical Systems Using Numerical Results, Neda Adib, Hafez Hadinejad Mahram
Neda Adib
Using multiple antennas in wireless communication systems proposes some degrees of freedom in system design, these degrees of freedom can be applied to improve the system reliability by using Space Time Block Coding (STBC) which provides diversity gain. Degrees of freedom also can be applied to increase the system capacity using Spatial Multiplexing (SM) methods. It is possible to achieve a trade-off between diversity gain and Spatial multiplexing gain. Selecting the method which provides best efficiency for a specific system is an important issue. In this paper we will show which space-time architecture achieves the best efficiency for a specific …
Cognitive State Estimation In Mobile Environments, Michael C. Dorneich, Santosh Mathan, Patricia May Ververs, Stephen D. Whitlow
Cognitive State Estimation In Mobile Environments, Michael C. Dorneich, Santosh Mathan, Patricia May Ververs, Stephen D. Whitlow
Michael C. Dorneich
This chapter presents the unique challenges encountered, difficult trade-offs required, and promising techniques em-ployed when moving cognitive state assessment from the la-boratory to a mobile field environment.
Throughput Enhancement Through Combined Fragmentation And Rate Method In Ieee 802.11b Wlans, Marek Bykowski, Karol Kowalik, Brian Keegan, Mark Davis
Throughput Enhancement Through Combined Fragmentation And Rate Method In Ieee 802.11b Wlans, Marek Bykowski, Karol Kowalik, Brian Keegan, Mark Davis
Conference papers
IEEE 802.11 allows for fragmentation tuning and rate selection. Their combined usage is referred sometimes to link adaptation. However, the algorithms of link adaptation are beyond the 802.11 standards. In this paper we investigate the benefits arising from proper use of link adaptation. Particularly, we develop a mathematical model describing the fragmented transmission in 802.11b. We examine potential benefits of it over AWGN and fading channels. More significantly we combine fragmentation tuning with bit-rate selection to yield the highest achievable throughput performance for any given channel conditions. Finally, we propose an algorithm that performs the optimal link adaptation.
High Performance Zno Varistors Prepared From Nanocrystalline Precursors For Miniaturised Electronic Devices, Suresh Pillai, Declan Mccormack, John Kelly, Raghavendra Ramesh
High Performance Zno Varistors Prepared From Nanocrystalline Precursors For Miniaturised Electronic Devices, Suresh Pillai, Declan Mccormack, John Kelly, Raghavendra Ramesh
Articles
An industrially viable solution-based processing route using minimal amounts of solvent has been used to prepare bulk quantity nanopowders (average particle size 15.3 nm) for the fabrication of ZnO varistors. The xerogels, calcined powders and sintered materials were fully characterised. The preparation of varistors from nanopowders has been optimised by studying the effect of temperature on grain growth, densification and breakdown voltage. The varistors are prepared by sintering at 1050 C for 2 hours, a temperature that is significantly lower than that used in the current industrial process. Highly dense varistor discs prepared from the sintered material produce devices, with …