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IEEE Globecom Workshops

作者： Prasanna Madhusudhanan Juan G. Restrepo Youjian Liu Timothy X Brown Department of Electrical Computer and Energy Engineering University of Colorado Boulder CO USA Department of Applied Mathematics University of Colorado Boulder CO USA Department of Electrical Computer and Energy Engineering Interdisciplinary Telecommunications Program University of Colorado Boulder CO USA

We study the downlink signal-to-interference ratio (SIR) in a multi-tier heterogeneous cellular network under the open and closed access schemes. Each tier is characterized by a base-station (BS) arrangement according to a homogeneous Poisson point process with certain density, constant transmission power and random shadow fading factors with arbitrary distribution. The mobile-station (MS) communicates with the BS that has the maximum instantaneous received power among those to which it is allowed access. The chosen BS provides coverage to the MS if the SIR is above a certain threshold determined by the BS's tier. The coverage probability and average rate expressions are derived for the open access scheme for any arbitrary SIR threshold assigned for each tier, and for the closed access scheme when the SIR thresholds are greater than one.

关键词： Fading Macrocell networks Random variables Measurement Computational modeling Femtocell networks Downlink

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The Usefulness of Overheard Information for Collision Avoidance in a Single-hop Underwater Acoustic Networks

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Procedia engineering 2012年 32卷 329-335页

作者： N. Chirdchoo W.-S. Soh K.C. Chua P. Kovintavewat W. Cheunta Telecommunication Program Faculty of Science and Technology Nakhon Pathom Rajabhat UniversityNakhon Pathom 73000 Thailand Department of Electrical and Computer Engineering National University of Singapore Singapore Computer Industrial Technology Program Faculty of Science and Technology Nakhon Pathom Rajabhat UniversityNakhon Pathom73000 Thailand

A MAC protocol that depends on overheard information for its collision avoidance, such as Carrier Sense Multiple Access (CSMA) [1], may not work well in underwater, due to the long propagation delay characteristic of an underwater acoustic (UWA) channel. In such channel, the overheard information may already become obsolete by the time it reaches the node and, thus, should not be taken into account in the collision avoidance mechanism. Intuitively, the degree of usefulness of overheard information plays an important role in determining the network performance for channel listening-based MAC protocols. In this paper, we analytically study the usefulness of overheard information for collision avoidance in two different channel listening-based MAC protocols: (1) CSMA [1] and (2) Aloha-CA [2]. From our study, it is shown that the overheard information is beneficial for collision avoidance only if certain conditions can be satisfied. More specifically, in order for a node that overhears an ongoing transmission to be able to utilize the extracted information for collision avoidance, the node must be within a bounded region that is determined by the relative positions of the sender and the receiver, the packet's transmission time, as well as the length of the packet's header. Based on this analysis, we also present the “usefulness index (U)” which is defined as the degree of usefulness of information overheard.

关键词： Underwater acoustic network MAC protocol design Channel listening Collision avoidance

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All dielectric zero-index metamaterials at optical frequencies

All dielectric zero-index metamaterials at optical frequenci...

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Conference on Optoelectronic and Microelectronic Materials and Devices

作者： J. Valentine P. Moitra Y. Yang W. Wang Department of Mechanical Engineering Vanderbilt University Nashville TN USA Interdisciplinary Program in Materials Science Vanderbilt University Nashville TN USA Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN USA

Dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. However, demonstrations of dielectric metamaterials have so far been limited to microwave and mid-infrared frequencies. In this work, we outline the development of purely dielectric zero-index metamaterials operating at optical frequencies. The metamaterial, formed from silicon rods, exhibits impedance matching with air, resulting in unity transmission at the zero-index point. Design and experimental realization of the metamaterials is presented. The metamaterials can potentially be used for a number of applications including compact lens systems, directional emitters, and transformation optics devices.

关键词： Metamaterials Magnetic materials Silicon Optical device fabrication Dielectrics Optical refraction

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Performance evaluation of D3LS and NCLS smart antenna in mobile communications

Performance evaluation of D3LS and NCLS smart antenna in mob...

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International Symposium on Antennas and Propagation (ISAP)

作者： Akkarat Boonpoonga Phichet Nilsuwan Jukkrit Tagapanij Phaophak Sirisuk Department of Electrical and Computer Engineering Faculty of Engineering King Mongkuts University of Technology North Bangkok Bangkok Thailand The Electrical Engineering Graduate Program Faculty of Engineering Mahanakorn University of Technology Bangkok Thailand Department of Telecommunication Engineering Mahanakorn University of Technology Bangkok Thailand International College King Mongkut's Institute of Technology Ladkrabang Bangkok Thailand

In this paper, the performance evaluation of a smart antenna using D3LS and NCLS algorithms has been presented. The simulations are conducted with the scenario of mobile communication systems. They have confirmed the feasibility of the D3LS and NCLS smart antenna applied to mobile communications. It should be note that the smart antenna employed in this paperis purely blind and single snapshot operation. The simulation results show good performance of the smart antenna.

关键词： Direction of arrival estimation Interference Mobile communication Mobile antennas Adaptive arrays Estimation

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Smart antenna using a combination of D3LS and NCLS algorithms

Smart antenna using a combination of D3LS and NCLS algorithm...

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International Conference on electrical engineering/Electronics, computer, telecommunications and Information Technology, ECTI-CON

作者： Phichet Nilsuwan Akkarat Boonpoonga Jukkrit Tagapanij Phaophak Sirisuk The Electrical Engineering Graduate Program Faculty of Engineering Mahanakorn University of Technology Bangkok Thailand Department of Electrical and Computer Engineering Faculty of Engineering King Mongkuts University of Technology North Bangkok Bangkok Thailand Department of Telecommunication Engineering Mahanakorn University of Technology Bangkok Thailand International College King Mongkut's Institute of Technology Ladkmbang Bangkok Thailand

ISBN: (纸本)9781467320269

This paper presents a smart antenna system using a combination of nonconventional least square (NCLS) optimization and direct data domain least square (D3LS) for direction-of-arrival (DOA) estimation and beamforming, respectively. In the proposed system, NCLS optimization is utilized to estimate DOA of incoming signal first. The estimated DOA is then assisted for initial processing of D3LS in beamforming. The performance in term of estimated signal amplitude and estimated DOA of the proposed system is evaluated via simulations.

关键词： Direction of arrival estimation Optimization Interference Adaptive arrays Estimation Arrays

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Intrinsic defects and conduction characteristics of Sc2O3 in thermionic cathode systems

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Physical Review B 2012年第5期86卷 054106-054106页

作者： Ryan M. Jacobs John H. Booske Dane Morgan Interdisciplinary Materials Science Program University of Wisconsin–Madison 1509 University Avenue Madison Wisconsin 53706 USA Department of Electrical and Computer Engineering University of Wisconsin–Madison 1415 Engineering Drive Madison Wisconsin 53706 USA Department of Materials Science and Engineering University of Wisconsin–Madison 1509 University Avenue Madison Wisconsin 53706 USA

Recent experimental observations indicate that bulk Sc2O3 (∼200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the observed high emitted current densities and overall superior emission properties over conventional thermionic emitters which do not contain Sc2O3. Here, we employ ab initio methods using both semilocal and hybrid functionals to calculate the intrinsic defect energetics of Sc and O vacancies and interstitials and their effects on the electronic properties of Sc2O3 in an effort to explain the good conduction of Sc2O3 observed in experiment. The defect energetics were used in an equilibrium defect model to calculate the concentrations of defects and their compensating electron and hole concentrations at equilibrium. Overall, our results indicate that the conductivity of Sc2O3 solely due to the presence of intrinsic defects in the cathode operating environment is unlikely to be high enough to maintain the magnitude of emitted current densities obtained from experiment, and that the presence of impurities is necessary to raise the conductivity of Sc2O3 to a high enough value to explain the current densities observed in experiment. The necessary minimum impurity concentration to impart sufficient electronic conduction is very small (approximately 7.5 × 10−3 ppm) and is probably present in all experiments.

关键词： SCANDIUM oxides CATHODES PRESSURE ELECTRIC conductors POINT defects PHYSICS experiments EQUILIBRIUM

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Frequency regulation and economic dispatch using integrated storage in a hybrid renewable grid

Frequency regulation and economic dispatch using integrated ...

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2011 International Conference on Energy, Automation and Signal, ICEAS - 2011

作者： Chhabra, Mohit Harnesswalla, Taha Lim, Michelle Barnes, Frank Department of Electrical Engineering University of Colorado Boulder CO 80303 United States Interdisciplinary Telecommunication Program University of Colorado Boulder CO 80303 United States

ISBN: (纸本)9781467301367

Increasing penetration of renewable energy sources on the electrical grid, with intermittent and fluctuating supply, leads to frequency variations that are excessive in nature. This paper demonstrates the use of energy storage devices as a solution to reduce these variations. In addition to grid stability, renewable operators are also interested in arbitrage operation. A simple dispatch strategy is provided, for operation of a wind farm coupled with a utility scale battery. © 2011 IEEE.

关键词： Scheduling

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On the interference due to cooperative cognitive radios in the presence of multiple low-power primary users

On the interference due to cooperative cognitive radios in t...

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2011 49th Annual Allerton Conference on Communication, Control, and Computing, Allerton 2011

作者： Madhusudhanan, Prasanna Brown, Timothy X. Liu, Youjian Department of Electrical Computer and Energy Engineering University of Colorado Boulder CO 80309-0425 United States Interdisciplinary Telecommunications Program University of Colorado Boulder CO 80309-0425 United States

ISBN: (纸本)9781457718168

We analyze a cognitive radio network where the low-power primary users and cognitive radio (CR) devices are distributed according to two independent homogeneous Poisson processes over the k-dimensional space, where k = 1, 2, 3. The CRs cooperate among themselves in detecting the beacons transmitted by the primary users, to ensure that they cause reduced interference at the primary users. A range of cooperative sensing schemes including the no (NC), partial (PC) and full cooperation (FC) scenarios are analyzed. Using the concepts of stochastic geometry, we assess the impact of the presence of the multiple primary users on the distribution of the signal-to-interference-plus-noise ratio (SINR) at a given primary user, for each cooperation scheme. Further, we characterize the improvement in the spectrum usage due to the CR operation in the licensed frequency band in terms of the probability, denoted by rho, that a CR is able to operate within the k-dimensional space. Using our calculations of the SINR at the primary user and rho, it is shown that the PC scheme achieves enhanced spectrum usage vis-a-vis the FC scheme and an improved SINR as compared to the NC scheme. Moreover, the PC scheme can be tuned in such a way that any desired value for spectrum usage and SINR is achievable. © 2011 IEEE.

关键词： Cognitive radio

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Accelerated oxidation of silicon due to x-ray irradiation

Accelerated oxidation of silicon due to x-ray irradiation

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12th European Conference on Radiation and Its Effects on Component and Systems, RADECS 2011

作者： Bhandaru, Shweta Zhang, En Xia Fleetwood, Daniel M. Reed, Robert A. Weller, Robert A. Weiss, Sharon M. Interdisciplinary Graduate Program in Material Science Vanderbilt University Nashville TN 37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN 37235 United States

Enhanced rates of oxide growth have been observed on silicon when exposed to high-energy x-ray irradiation. This observed effect could potentially be utilized for remote total ionizing dose-sensing applications. ©... 详细信息

ISBN: (纸本)9781457705878

关键词： Silicon

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Frequency regulation and economic dispatch using integrated storage in a hybrid renewable grid

Frequency regulation and economic dispatch using integrated ...

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International Conference on Energy, Automation, and Signal (ICEAS)

作者： Mohit Chhabra Taha Harnesswalla Michelle Lim Frank Barnes Department of Electrical Engineering University of Colorado Boulder CO USA Interdisciplinary Telecommunication Program University of Colorado Boulder CO USA

关键词： Batteries Frequency control Smoothing methods Renewable energy resources Real time systems Time frequency analysis

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