Página 34 dos resultados de 2566 itens digitais encontrados em 0.037 segundos

Performance of IEEE 802.11a wireless LAN standard over frequency-selective, slow, ricean fading channels

Kao, Chi-Han
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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Approved for public release, distribution is unlimited; With the rapidly growing demand for more reliable and higher data rate wireless communications, the Institute of the Electrical and Electronics Engineers (IEEE) 802.11 working group approved a standard for 5 GHz band, wireless local area networks (WLAN) in 1999. This standard, IEEE 802.11a, supports data rates from 6 up to 54 Mbps, and uses orthogonal frequency division multiplexing (OFDM) for transmission in indoor wireless environments. This thesis examines the performance of the IEEE 802.11a standard for different combinations of sub-carrier modulation type and code rate and determines the signal-to-noise ratio required to obtain a probability of bit error b P of 10-5. The channel is modeled as a frequency-selective, slow, Ricean fading channel with additive white Gaussian noise (AWGN). Contrary to expectations, for the combinations of sub-carrier modulation type and code rate utilized by the IEEE 802.11a standard, some of the higher data rate combinations outperform some of the lower data rate combinations. On the other hand, the results also show significant coding gain when applying convolutional coding with Viterbi decoding, and hence highlight the importance of forward error correction (FEC) coding to the performance of wireless communications systems.

JPEG2000 image compression and error resilience for transmission over wireless channels

Kamaras, Konstantinos
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado
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Approved for public release, distribution is unlimited; This thesis examines the compression performance of the JPEG2000 standard for image transmission over noisy channels. Other features of the standard, such as error resilience and region of interest, have been studied and their effectiveness tested on several images. The JPEG2000 still image compression standard has provided higher compressions performance with lower distortion and better image quality than JPEG. JPEG2000 has the capability to define regions of interest of any shape and size and code the selected regions with a higher fidelity than the rest of the image. Compressed image data is transmitted over a noisy wireless channel based on Gilbert-Eliot model, which simulates both isolated and burst errors. JPEG2000 error resilient tools are used to allow the decoder to detect and conceal errors introduced in the channel. The results indicate up to 10 dB improvement in the peak signal to noise ratio when these tools are used.

Increasing prompt response from impulse radiating antenna by aperture shaping

Baretela, Michael J.
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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Approved for public release, distribution is unlimited; In order to improve the prompt response from an impulse radiating antenna (IRA)number of studies have suggested controlling the spatial distribution of the aperture fields by changing the feed arm angle. Other work has suggested that proper shaping of the aperture can further enhance the radiated signal for a given feed structure. This paper shows how the radiated prompt response can be maximized for a given feed arm configuration by shaping the aperture to eliminate fields orientated in the wrong direction. The percent increase in the prompt radiated electric field for a 200 . IRA with a ideally shaped aperture compared to a standard circular aperture ranged from 0.42% to 39.94% depending on the input electrode angle. For the most common electrode angles of 45Ê» and 60Ê» the increases are 6.00% and 16.63% respectively.

Hardware Assistance for Trustworthy Systems Through 3-D-Integration

Valamehr, Jonathan; Tiwari, Mohit; Sherwood, Timothy; Kastner, Ryan
Fonte: Association for Computing Machinery (ACM) Publicador: Association for Computing Machinery (ACM)
Tipo: Artigo de Revista Científica
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Hardware resources are abundant; state-of-the-art processors have over one billion transistors. Yet for a variety of reasons, specialized hardware functions for high assurance processing are seldom (i.e., a couple of features per vendor over twenty years) integrated into these commodity processors, despite a small flurry of late (e.g., ARM TrustZone, IntelVT-x/VT-d and AMD-V/AMD-Vi, Intel TXT and AMD SVM, and Intel AES-NI). Furthermore, as chips increase in complexity, trustworthy processing of sensitive information can become increasingly difficult to achieve due to extensive on-chip resource sharing and the lack of corresponding protection mechanisms. In this paper, we introduce a method to enhance the security of commodity integrated circuits, using minor modifications, in conjunction with a separate integrated circuit that can provide monitoring, access control, and other useful security functions. We introduce a new architecture using a separate control plane, stacked using 3-D integration, that allows for the function and economics of specialized security mechanisms, not available from a coprocessor alone, to be integrated with the underlying commodity computing hardware. We first describe a general methodology to modify the host computation plane by attaching an optional control plane using 3-D integration. In a developed example we show how this approach can increase system trustworthiness...

Line and circle formation of distributed autonomous mobile robots with limited sensor range

Albayrak, Okay
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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Approved for public release; distribution is unlimited.; In the literature, formation problems for idealized distributed autonomous mobile robots were studied. Idealized robots are represented by a dimensionless point, are able to instantaneously move in any direction and are equipped with perfect range sensors. In this thesis, line and circle formation problems of distributed mobile robots that are subjected to physical constraints are addressed. It is assumed that mobile robots have physical dimensions, and their motions are governed by physical laws. They are equipped with sonar and infrared sensors in which sensor ranges are limited. A new line algorithm based on least-square line fitting, a new circle algorithm, and a merge algorithm are presented. All the algorithms are developed with consideration of physical robots and realistic sensors, and are validated through extensive simulations. Formation problems for mobile robots with limited visibility are also studied. In this case, robots are assumed to be randomly distributed in a large rectangular field such that one robot may not see other robots. An algorithm is developed that makes each robot converge to the center of the field before executing a line or circle algorithm.

Time domain simulation MFSK communications system performance in the presence of wideband noise and co-channel interference

Tsiridis, Konstantinos
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
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Approved for public release; distribution is unlimited; In this thesis models of MFSK digital communications systems were developed using Matlab Simulink and Communications Toolbox. The models were employed to verify MFSK performance in the presence of additive noise and predict MFSK performance for additive noise and co-channel interference. Results are presented for bit-error rate as functions of the signal-to-noise and signal- to-interference power ratios. The results for coherent detection of MFSK (M=2,4, 8) in the presence of additive white Gaussian noise show excellent agreement with the theory. On the other hand, simulation results for the probability of bit error for non- coherent detection of MFSK differ (-21% average) from the theory suggesting a possible systematic error in the Communications Toolbox implementation of the non-coherent MFSK detection.

Analysis of a proposed third generation (3G) mobile communication standard, time division-synchronous code division mulitple access (TD-SCDMA)

Paulson, Donald H.
Fonte: Monterey, California: Naval Postgraduate School, 2002. Publicador: Monterey, California: Naval Postgraduate School, 2002.
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With a growing number of consumers utilizing the Internet, companies have foreseen a consumer demand for high-speed wireless access. Since current mobile cellular systems can transfer at most 115.2 kbps per user, a third generation of mobile cellular service has been under development by various organizations since 1997. This new generation of technology will support data rates up to 2 Mbps for stationary mobiles and up to 144 kbps for vehicular traffic. This thesis focuses mainly on TD-SCDMA, one of many candidates submitted to the International Telecommunications Union for third generation review. The standard, developed in China by the Chinese Academy of Telecommunications Technology, employs both code-division multiple access and time-division duplexing to support both forward and reverse transmissions on one physical layer. This aspect, along with other common features of TD-SCDMA, will be studied and evaluated to determine if this new technology is a viable option for future commercial or military deployment.

A hierarchical approach to the classification of digital modulation types in multipath environments

Fargues, Monique P.; Hatzichristos, G.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório
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The views expressed in this report are those of the author and do not reflect the offical policy or position of the Department of Defense or the United States Government.; This study presents a hierarchical classification approach to the classification of digital modulation schemes of types 2,4,8-PSK, 2,4,8-FSK and 16,64,256-QAM in low SNR levels and multipath propagation channel conditions. A hierarchical tree-based classification approach is selected as it leads to a relatively simple overall scheme with few parameters needed to differentiate between the various modulation types. Back-propagation neural network units are adopted at each tree node because they offer the flexibility needed to cope with varying propagation environments, as is the case in real-world communications. The selection of robust and well-defined higher-order statistics-based class features is considered and a small number of cumulates and moments chosen to differentiate between all various types of modulation types, except for specific M-QAM types. Simulations show that M-QAM types may be so affected by multipath and fading that higher-order statistic parameters become of very limited use. While being part of the hierarchical procedure, the identification of specific M-QAM types is conducted via equalization algorithms. Extensive simulations show overall classification performances to be strongly affected by the amount of multipath distortion and noise in the transmission channels. Results also show a much higher sensitivity of high-order M-QAM types to fading and multipath propagation distortions than other modulation types.

Evaluation and extensions of the probabilistic multi-hypothesis tracking algorithm to cluttered environments

Hutchins, Robert G.; Dunham, D. T.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório
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This research examines the probabilistic multi-hypothesis tracker (PHMT), a batch mode, empirical, Bayesian data association and tracking algorithm. Like a traditional multi-hypothesis tracker (MHT), track estimation is deferred until more conclusive data is gathered. However, unlike a traditional algorithm, PMHT does not attempt to enumerate all possible combinations of feasible data association links, but uses a probabilistic structure derived using expectation maximization. This study focuses on two issues: the behavior of the PMHT algorithm in clutter and algorithm initialization in clutter. We also compare performance between this algorithm and other algorithms, including a nearest neighbor tracker, a probabilistic data association filter (PDAF), and a traditional measurement oriented MHT algorithm.

A ring model for local mobile radio communications with variable packet length

Banh, Dennis V.
Fonte: Monterey, California: Naval Postgraduate School Publicador: Monterey, California: Naval Postgraduate School
Tipo: Tese de Doutorado
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Approved for public release; distribution unlimited.; This thesis presents an analysis of the performance of a local mobile radio communications system utilizing the Aloha random access protocol with variable length packets. The capture phenomenon due to the nearfar effect that enhances the performance of the system is investigated. A tagged packet will capture the base station if its signal-to-interference ratio exceeds a threshold gamma sub zero. Because of the nearfar effect, users near the base station typically have a stronger signal than those farther away. A multiple ring model is used to alleviate this problem. Users in one ring employ different retransmission strategy from those in other rings. A shorter retransmission delay is allocated to users in rings farther from the base station than those closer to the base station in order to achieve approximately the same average delay throughout the network regardless of location.

Study of sound propagation in a wedge-shaped ocean and comparison with other methods

Nassopoulos, George
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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Approved for public release; distribution is unlimited.; After several years of research, the image theory has been found acceptable to solve the sound propagation problem within a wedge-shaped fluid overlying either a slow or a fast bottom. Some further observations where done in this research. The primary purpose was the development and computer application of a new analysis, the doublet analysis, based on the image theory. In this analysis, the features of the image theory are studied from another point of view, based on a collection of acoustic doublets.

A computer code (SKINTEMP) for predicting transient missile and aircraft heat transfer characteristics

Terrence, Mary
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
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Software development in weapon systems is extremely challenging and has become a significant source of problems in DOD programs. The purpose of this thesis is to identify and document strategies and techniques for program offices to use in managing these software problems. This thesis documents the success of the Enhanced Position Location Responding System in applying corrective software management actions to specific problems encountered. Lessons learned have been drawn from the analysis and generalized for application to other DOD programs. The principal finding is that an effective software corrective action plan requires a focused effort devoted to identifying and correcting all software deficiencies. This is accomplished before further developmental work requiring software is attempted. The thesis concludes that an astute program office should be prepared to implement and manage this type of software corrective action plan. Two primary recommendations are for the development of a DOD policy on the management of software corrective action plan. Two primary recommendations are for the development of a DOD policy on the management of software corrective action and the development of a DOD model for software corrective action by program offices.

Optimizing gas generator efficiency in a forward operating base using an energy management system

Kelly, Ryan L.
Fonte: Monterey, California: Naval Postgraduate School Publicador: Monterey, California: Naval Postgraduate School
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Approved for public release; distribution is unlimited; A Forward Operating Base (FOB) is designed to support combat operations in an austere environment, which often lacks pre-existing infrastructure. On-site diesel generators are the primary source of FOB electricity. Traditionally, each generator is connected to its own set of loads and operates independently from other generators. The benefits of transitioning from traditional generator employment to an alternative architecture using an Energy Management System (EMS) were investigated in this thesis. The EMS provides an interface between power sources, loads, and energy storage elements to form a microgrid. Using power electronics and programmable logic, the EMS provides capabilities such as power source selection, power metering, flow control, and peak power management. These capabilities enable more efficient generator utilization by matching real time load demand to the smallest capable power source, reducing overall fuel consumption. The EMS offers redundancy as it can connect any one of multiple power sources to critical loads. A hardware-based laboratory experiment demonstrated the ability to transition from one power source to another while providing uninterrupted current to the load. The results of the experiment validate a Simulink model of the EMS. An example load profile was applied to the model to compare overall fuel consumption between the traditional architecture and EMS-enabled microgrid.

Analysis of input and output configurations for use in four-valued programmable logic arrays

Kerkhoff, Hans G.; Butler, Jon T.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, it may not be copyrighted.; Proceedings of the IEE-E: Computers and Digital Techniques, Vol. 134, No. 4, pp. 168-176, July 1987; As in binary, a multiple-valued programmable logic array (PLA) realises a sum-of-products, expression specified by the user. However, in multiple-valued logic, there are many more operations than in binary, and an important question is the choice of operations with provides the greatest number of functions for a given chip area. In this paper, we analyse various PLA configurations using operations realised in the peristaltic multiple-valued CCD technology. We compare a multiple-valued CCD PLA implementation with four other proposed designs and show that there is a significant different in chip area required to realise the same set of functions. The basis of comparison is the set of 4-valued unary functions.

Properties of c-correctability in self-diagnosing systems

Rosen, Yonina; Butler, Jon T.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, it may not be copyrighted.; Proceedings of the 26th Annual Allerton Conference on Communication, Control, and Computing, Sept. 1988, regular (full) paper, pp. 408-416 (Unrefereed); We propose a distributed disabling algorithm for a multiprocessing system in which each processor or unit is prevented from doing computation when it fails some number of tests by other units. The goal is to disable all faulty units and to enable all fault-free units. Specifically, a unit is disabled if it fails d or more tests by enabled units (d-disabling rule). A multiprocessor system is c-correctable using the d-disabling rule if all faulty units are permanently disabled and all fault-free units are permanently enabled after a finite number of applications of the disabling rule, provided there are no more thna c faulty units. This models an unattended system where the removal of faulty units is done locally by simple and reliable circuitry. We give a sufficient condition for c-correctability in general systems and a necessary and sufficient condition in general systems where c < d. Then...

Multiple-valued PLA minimization by concurrent multiple and mixed simulated annealing

Yildirim, Cem; Yang, Chyan; Butler, Jon T.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, it may not be copyrighted.; Proceedings of the 23rd International Symposium on Multiple-Valued Logic, May 1993, pp. 17-23; We analyze simulated annealing applied to multiple-valued programmable logic array (MVL PLA) design. Of spec@c interest is the use of parallel processors. We consider the use of loosely-coupled, coarse- grainedparallel systems, and study the relationship between the quality of the solution and computation time, on the one hand, and simulated annealing parameters, start temperature, cooling rate, etc., on the other. We also investigate simulated annealing where there is a mixture of move types. The mixed move approach provides improvement in both the number of product terms and computation time.

Floating-point numerical function generators using EVMDDs for monotone elementary functions

Nagayama, Shinobu; Sasao, Tsutomu; Butler, Jon T.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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39th International Symposium on Multiple-Valued Logic (ISMVL 2009) May 21-23, 2009, pp.349-355.; This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, it may not be copyrighted.; This paper proposes a design method for floating-point numerical function generators (NFGs) using multi-valued decision diagrams (MDDs). Our method applies to monotone elementary functions in which real values are converted into integer values that are presented by edge-valued MDDs (EVMDDs). We show that EVMDDs use fewer nodes by one or two orders of magnitude than two other types of decision diagrams, MTBDDs and BMDs . EVMDDs produce fast and compact floating-point NFGs for real-valued elementary functions, with a speed improvement of 86% over a recently proposed floating-point implementation.

Logic functions for cryptography - A tutorial

Sasao, Tsutomu; Butler, Jon T.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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Reed-Muller Workshop (RM2009), pp.127-136, May 23-24, 2009.; This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, it may not be copyrighted.; Significant research has been done on bent functions, yet researchers in switching theory have paid little attention to this important topic. The goal of this paper is to provide a concise exposition. Bent functions are the most nonlinear functions among n-variable switching functions, and are useful in cryptographic applications. This paper discusses three other kinds of cyptographic properties, strict avalanche criterion, propation criterion, and correlation immunity. We discuess known properties, as well as open questions. It assumes the reader is familiar with switching circuit theory. Familiarity with Reed-Muller expansions is helpful, but not essential.

Terrain analysis using Landsat thematic mapper imagery

Michael, Gerald T.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
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Approved for public release; distribution is unlimited; This thesis examined two sites from a Landsat scene of portions of Honduras and Nicaragua. One site was examined for potential water obstacles, and the other was examined for cover and concealment provided by vegetation. The results suggest that potential water obstacles can be detected. It is not clear if vegetative cover and concealment can be reliably detected. A study using better ground reference information than was available is necessary to answer that question. Several unsupervised classification algorithms were used and compared. A histogram clustering algorithm followed by a minimum distance classifier provided results comparable to the much slower K-means and isodatatype algorithms. Several methods to reduce the dimensionality of the classification problem were examined, including band subsets, between-band ratios, the principal component transformation, and the tasseled cap transformations. Band subsets provided adequate accuracy and is the easiest method to implement.

Second-layer polysilicon structures for gate end-around leakage-current compensation in bulk CMOS ICs

Fouts, Douglas J.; McKerrow, Gary R.; Lum, Gary K.; Noe, Sidney S.; Lambley, Andrew S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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CMOS integrated circuits (ICs) operating in space or other radiation environments can suffer from three different reliability problems due to the radiation: total dose effects, dose rate effects, and single event effects. The two most significant total-dose reliability problems are subthreshold, gat, end-around leakage current and threshold voltage shift. This article documents the theory, design, implementation, and testing of new, second-layer polysilicon structures that can compensate for radiation-induced, subthreshold, gate, end-around, leakage current. Second-layer polysilicon is available in many commercial, bulk CMOS processes and is normally used for floating-gate devices, such as EEPROMs and FPLAs, and charge-coupled devices such as CCD focal plan arrays. The use of the described structures in CMOS ICs would allow radiation tolerant ICs to be fabricated with commercial, bulk CMOS processors, greatly reducing manufacturing costs when compared to the cost of fabricating ICs on dedicated, radiation-hardened process lines.