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Interference characterization and suppression for multiuser direct-sequence spread-spectrum system

Fan, Mingxi, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 184 p.; 6539812 bytes; 6539619 bytes; application/pdf; application/pdf
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In this thesis we investigate efficient modulation and detection techniques for the uplink (i.e. transmission from mobile to base station) of a DS-CDMA network. Specifically, the thesis contains three parts. In the first part, we focus on the mobile transmitter. In particular, we evaluate and compare the spectral efficiency of two promising variable rate DS-CDMA transmission techniques, multicode (MCD) and variable-spreading-gain (VSG), under the presence of multiple-access (user-to-user) interferences (MAI) and multipath interferences. The uniqueness of our study is that in bit-error-rate evaluation, instead of approximating the interference as Gaussian noise (which has been done in most of the previous studies), we incorporate both power and distribution of interferences into consideration. We show where the Gaussian assumption may give misleading answers and how our results in these cases are different from those obtained in the past. In part two and three of the thesis, we focus on the base station receiver. Specifically, we present effective joint detection techniques that have good performance-complexity tradeoff. Part two of the thesis introduces a class of novel multistage parallel interference cancellation algorithms based on stage-by-stage minimum mean-squared error (MMSE) optimization. We show that this scheme is capable of achieving significantly better performance than other algorithms with similar complexity. Part three of the thesis presents a low-complexity dual-mode multiuser detector that dynamically switches its detection mode between the matched-filter receiver and the decorrelator. We show that this detector is capable of achieving the performance of a decorrelator but with significant savings in processing power and complexity.; by Mingxi Fan.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

Cooperative diversity in wireless networks : algorithms and architectures

Laneman, J. Nicholas
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 187 p.; 6889171 bytes; 6888980 bytes; application/pdf; application/pdf
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To effectively combat multipath fading across multiple protocol layers in wireless networks, this dissertation develops energy-efficient algorithms that employ certain kinds of cooperation among terminals, and illustrates how one might incorporate these algorithms into various network architectures. In these techniques, sets of terminals relay signals for each other to create a virtual antenna array, trading off the costs-in power, bandwidth, and complexity-for the greater benefits gained by exploiting spatial diversity in the channel. By contrast, classical network architectures only employ point-to-point transmission and thus forego these benefits. After summarizing a model for the wireless channel, we present various practical cooperative diversity algorithms based upon different types of relay processing and re-encoding, both with and without limited feedback from the ultimate receivers. Using information theoretic tools, we show that all these algorithms can achieve full spatial diversity, as if each terminal had as many transmit antennas as the entire set of cooperating terminals. Such diversity gains translate into greatly improved robustness to fading for the same transmit power, or substantially reduced transmit power for the same level of performance. For example...

Predicting the beta-trefoil fold from protein sequence data

Menke, Matthew Ewald, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 47 p.; 1848213 bytes; 1848021 bytes; application/pdf; application/pdf
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A method is presented that uses [beta]-strand interactions at both the sequence and the atomic level, to predict the beta-structural motifs in protein sequences. A program called Wrap-and-Pack implements this method, and is shown to recognize β-trefoils, an important class of globular β-structures, in the Protein Data Bank with 92% specificity and 92.3% sensitivity in cross-validation. It is demonstrated that Wrap-and-Pack learns each of the ten known SCOP β-trefoil families, when trained primarily on β-structures that are not β-trefoils, together with 3D structures of known β-trefoils from outside the family. Wrap-and-Pack also predicts many proteins of unknown structure to be β-trefoils. The computational method used here may generalize to other β-structures for which strand topology and profiles of residue accessibility are well conserved.; by Matthew Ewald Menke.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.; Includes bibliographical references (p. 45-47).

Photovoltaic devices using photosynthetic protein complexes

Das, Rupa, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 leaves; 2334411 bytes; 2334219 bytes; application/pdf; application/pdf
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Photosynthetic proteins have been used as an active material in design of organic solar cells. Traditional organic solar cells have the limitation of not being able to absorb light in the visible-NIR region of the solar spectrum. This region corresponds to over 70% power of the total solar radiation. Using molecular proteins obtained from nature these limitations can be overcome. Biological photosynthetic complexes contain reaction centers with a quantum yield of >95% and a bandgap of less than l.leV allowing absorption in the 600-11 00nm visible-NIR range. Two types of photosynthetic complexes are employed to demonstrate the generality of the solid state integration technique to make solar cells. The simplest photosynthetic complex used is a bacterial reaction center (RC), isolated from the purple bacterium R. sphaeroides. The other protein being used is Photosystem I (PSI), a much larger complex, which is isolated from spinach chloroplasts. Electronic integration of devices is achieved by depositing organic semiconducting protective layer over a self-assembled monolayer of photosynthetic reaction centers oriented via an engineered metal-affinity polyhistidine tag. Various analytical and spectroscopic techniques have been used to examine solution spectrum and solid state device characteristics. Reasonable efficiencies have been obtained which demonstrates applicability of such techniques. The efficiency obtained is higher than a wet cell made using same proteins. The next immediate goal is to optimize processing conditions and therefore improve efficiency to reach levels comparable traditional organic solar cells.; by Rupa Das.; Thesis (S.M.)--Massachusetts Institute of Technology...

Fine-grained fault-tolerance : reliability as a fungible resource

Impens, François, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 134 p.; 4982767 bytes; 4982576 bytes; application/pdf; application/pdf
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The traditional design of logic circuits, based on reliable components, is incompatible with the next generation of devices relying on fewer resources and subject to high rates of soft errors. These allow a trade-off between failure probability and their space and power consumption. Using this, we show that reliability can be a fungible resource, interconvertible with other physical resources in multiple, unusual ways, via fault-tolerant architectures. This thesis investigates the potentialities offered by a fault-tolerant design in devices whose reliability is limited by shrinking resources. Surprisingly, we find that an appropriate use of structured redundancy could lead to more efficient components. The performance of a fine-grained multiplexed design can indeed be systematically evaluated in terms of resource savings and reliability improvement. This analysis is applied to characterize technologies at the nano scale, such as molecular electronics, which may benefit enormously by fault-tolerant designs.; by François Impens.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.; Includes bibliographical references (p. 131-134).

Modeling and measurement of intermolecular interaction forces between cartilage ECM macromolecules

Dean, Delphine Marguerite Denise, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 151 p.; 8276401 bytes; 8296751 bytes; application/pdf; application/pdf
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The mechanical properties of cartilage tissue depend largely on the macromolecules that make up its extracellular matrix (ECM). Aggrecan is the most abundant proteoglycan in articular cartilage. It is composed of a core protein with highly charged, densely packed glycosaminoglycan (GAG) side chains, which are responsible for [approximately] 50% of the equilibrium compressive stiffness of the tissue. Using atomic force microscopy (AFM) and high resolution force spectroscopy (HRFS), it is now possible to directly measure nanoscale interactions between ECM macromolecules in physiologically relevant aqueous solution conditions. In order to interpret these data and compare them to macroscopic tissue measurements, a combination of experiments and theoretical modeling must be used. In this thesis, a new molecular-scale continuum Poisson-Boltzmann (PB)-based model was developed to predict the intermolecular interactions between GAG macromolecules by taking into account nanoscale space varying electric potential and fields between neighboring GAGs. A rod-like charge density distribution describing the time averaged space occupied by a single GAG chain was formulated. The spacing and size of the rods greatly influenced the calculated force even when the total charge was kept constant. The theoretical simulations described HRFS experimental data of the normal interaction force between two surfaces chemically end-grafted with an array of GAGs ("brushes") more accurately than simpler models which approximate the GAG charge as a homogeneous volume or planar surface charge. Taken together...

Techniques for mitigating congestion in wireless sensor networks

Hull, Bret Warren, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 105 p.; 5985493 bytes; 5997971 bytes; application/pdf; application/pdf
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Network congestion occurs when offered traffic load exceeds available capacity at any point in a network. In wireless sensor networks, congestion causes overall channel quality to degrade and loss rates to rise, leads to buffer drops and increased delays (as in wired networks), and tends to be grossly unfair toward nodes whose data has to traverse a larger number of radio hops. Congestion control in wired networks is usually done using end-to-end and network-layer mechanisms acting in concert. However, this approach does not solve the problem in wireless networks because concurrent radio transmissions on different "links" interact with and affect each other, and because radio channel quality shows high variability over multiple time-scales. In this thesis, we examine three techniques that span different layers of the traditional protocol stack: hop-by-hop flow control, rate limiting source traffic when transit traffic is present, and a prioritized medium access control (MAC) protocol. We implement these techniques and present experimental results from a 55-node in-building wireless sensor network. We demonstrate that the combination of these techniques can improve network efficiency by a factor of three under realistic workloads.; by Bret Warren Hull.; Thesis (S.M.)--Massachusetts Institute of Technology...

Carbon nanotube applications for CMOS back-end processing

Wu, Tan Mau, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75 p.; 3719310 bytes; 3727171 bytes; application/pdf; application/pdf
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Carbon nanotubes are a recently discovered material with excellent mechanical, thermal, and electronic properties. In particular, they are potential ballistic transporters and are theorized to have thermal conductivities greater than any other material currently known. In this thesis, we will examine two possible applications of carbon nanotubes in CMOS back-end processing. The first application is as a replacement for copper interconnects. As interconnect line widths shrink, the electrical resistivity of copper will rise dramatically due to surface scattering effects. Carbon nanotube ballistic transporters may be able to overcome this obstacle, as well as being able to withstand current densities much greater than copper. The second application is an enhanced thermal conductivity dielectric for thermal management purposes. Carbon nanotube-oxide composites demonstrate improved thermal characteristics, and integration into CMOS technology may be able to alleviate some of the heat-removal and distribution problems future integrated circuits will face. We will also examine some of the processing techniques that will be necessary for carbon nanotube commercial deployment. Some of the issues we will discuss are nanotube growth, purification...

Perceptual picture emphasis using texture power maps

Su, Sara Lee, 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 p.; 4947146 bytes; 4954249 bytes; application/pdf; application/pdf
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Applying selective emphasis to photographs is a critical aspect of the visual design process. There is evidence from psychophysics that contrast in texture is a key contributor to saliency in an image, yet unlike other low-level perceptual features, texture cannot be directly modified with existing image-processing software. We present a post-processing technique to subtly change the salience of regions of an image by modifying spatial variation in texture. Our method is inspired by computational models of visual attention that capture sensitivity to outliers in local feature distributions. We use the steerable pyramid, which encodes multi-scale oriented image features and compute a set of power maps which capture the local texture content at each scale and orientation. With this representation, texture variation can be modified to selectively add or remove emphasis in the image. Two user studies provide qualitative and quantitative psychophysical validation of our approach.; by Sara Lee Su.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; Includes bibliographical references (p. 65-70).

Declarative symbolic pure-logic model checking

Shlyakhter, Ilya, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 181 p.; 9773619 bytes; 9796412 bytes; application/pdf; application/pdf
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Model checking, a technique for findings errors in systems, involves building a formal model that describes possible system behaviors and correctness conditions, and using a tool to search for model behaviors violating correctness properties. Existing model checkers are well-suited for analyzing control-intensive algorithms (e.g. network protocols with simple node state). Many important analyses, however, fall outside the capabilities of existing model checkers. Examples include checking algorithms with complex state, distributed algorithms over all network topologies, and highly declarative models. This thesis addresses the problem of building an efficient model checker that overcomes these limitations. The work builds on Alloy, a relational modeling language. Previous work has defined the language and shown that it can be analyzed by translation to SAT. The primary contributions of this thesis include: a modeling paradigm for describing complex structures in Alloy; significant improvements in scalability of the analyzer; and improvements in usability of the analyzer via addition of a debugger for over constraints. Together, these changes make model-checking practical for important new classes of analyses. While the work was done in the context of Alloy...

Design and analysis of a two-dimensional camera array

Yang, Jason C. (Jason Chieh-Sheng), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 158 p.; 9544111 bytes; 9565776 bytes; application/pdf; application/pdf
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I present the design and analysis of a two-dimensional camera array for virtual studio applications. It is possible to substitute conventional cameras and motion control devices with a real-time, light field camera array. I discuss a variety of camera architectures and describe a prototype system based on the "finite-viewpoints" design that allows multiple viewers to navigate virtual cameras in a dynamically changing light field captured in real time. The light field camera consists of 64 commodity video cameras connected to off-the-shelf computers. I employ a distributed rendering algorithm that overcomes the data bandwidth problems inherent in capturing light fields by selectively transmitting only those portions of the video streams that contribute to the desired virtual view. I also quantify the capabilities of a virtual camera rendered from a camera array in terms of the range of motion, range of rotation, and effective resolution. I compare these results to other configurations. From this analysis I provide a method for camera array designers to select and configure cameras to meet desired specifications. I demonstrate the system and the conclusions of the analysis with a number of examples that exploit dynamic light fields.; by Jason Chieh-Sheng Yang.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

Equivalence checking of retimed circuits

Netolická, Karolína
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 25 p.; 520268 bytes; 543745 bytes; application/pdf; application/pdf
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This thesis addresses the problem of verifying the equivalence of two circuits, one or both of which have undergone register retiming as well as logic resynthesis. The aim of the thesis is to improve the ability of Formality, an equivalence checking tool written at Synopsys, to handle retimed circuits. At the beginning of this project Formality already had an implementation of peripheral retiming, an algorithm that can handle a large set of retimed circuits. In this thesis, I explain the performance, usability and special case coverage problems found in the original implementation. I review other retiming verification algorithms and conclude that none of them would perform satisfactorily in Formality. Finally, I explain the modifications made to peripheral retiming in order to solve some of the identified issues and propose partial solutions for the problems that have not been solved yet.; by Karolína Netolická.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; Includes bibliographical references (p. 25).

Multi-source contingency clustering

Bouvrie, Jacob V
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 96 p.; 4795615 bytes; 4800564 bytes; application/pdf; application/pdf
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This thesis examines the problem of clustering multiple, related sets of data simultaneously. Given datasets which are in some way connected (e.g. temporally) but which do not necessarily share label compatibility, we exploit co-occurrence in- formation in the form of normalized multidimensional contingency tables in order to recover robust mappings between data points and clusters for each of the individual data sources. We outline a unifying formalism by which one might approach cross-channel clustering problems, and begin by defining an information-theoretic objective function that is small when the clustering can be expected to be good. We then propose and explore several multi-source algorithms for optimizing this and other relevant objective functions, borrowing ideas from both continuous and discrete optimization methods. More specifically, we adapt gradient-based techniques, simulated annealing, and spectral clustering to the multi-source clustering problem. Finally, we apply the proposed algorithms to a multi-source human identification task, where the overall goal is to cluster grayscale face images according to identity, using additional temporally connected features. It is our hope that the proposed multi-source clustering framework can ultimately shed light on the problem of when and how models might be automatically created to account for...

Enhancing availability and security through boundless memory blocks

Cadar, Cristian
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 52 leaves; 2070965 bytes; 2071920 bytes; application/pdf; application/pdf
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We present a new technique, boundless memory blocks, that automatically eliminates buffer overflow errors, enabling programs to continue to execute through memory errors without memory corruption. Buffer overflow vulnerabilities are caused by programming errors that allow an attacker to cause the program to write beyond the bounds of an allocated memory block to corrupt other data structures. The standard way to exploit a buffer overflow vulnerability involves a request that is too large for the buffer intended to hold it. The buffer overflow error causes the program to write part of the request beyond the bounds of the buffer, corrupting the address space of the program and causing the program to execute injected code contained in the request. Our boundless memory blocks compiler inserts checks that dynamically detect all out of bounds accesses. When it detects an out of bounds write, it stores the value away in a hash. Our compiler can then return the stored value as the result of an out of bounds read to that address. In the case of uninitialized addresses, our compiler simply returns a predefined value. We have acquired several widely used open source applications (Apache, Sendmail, Pine, Mutt, and Midnight Commander). With standard compilers...

A global maximum power point tracking DC-DC converter

Duncan, Joseph, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 80 p.; 2261802 bytes; 2265322 bytes; application/pdf; application/pdf
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This thesis describes the design, and validation of a maximum power point tracking DC-DC converter capable of following the true global maximum power point in the presence of other local maximum. It does this without the use of costly components such as analog-to-digital converters and microprocessors. It substantially increases the efficiency of solar power conversion by allowing solar cells to operate at their ideal operating point regardless of changes in load, and illumination. The converter switches between a dithering algorithm which tracks the local maximum and a global search algorithm for ensuring that the converter is operating at the true global maximum.; by Joseph Duncan.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; Includes bibliographical references (p. 79-80).

Communication between layers in biological transcriptional networks

Tsankov, Alex
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves; 2107488 bytes; 2120757 bytes; application/pdf; application/pdf
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Chromatin-immunoprecipitation experiments in combination with microarrays (known as ChIP-chip) have recently allowed biologists to map where proteins bind in the yeast genome. The combinatorial binding of different proteins at or near a gene controls the transcription (copying) of a gene and the production of the functional RNA or protein that the gene encodes. Therefore, ChIP-chip data provides powerful insight on how genes and gene products (i.e., proteins, RNA) interact and regulate one another in the underlying network of the cell. Much of the current work in modeling yeast transcriptional networks focuses on the regulatory effect of a class of proteins known as transcription factors (TF). However, other sets of factors also influence transcription, including histone modifications and states (HS), histone modifiers (HM) and remodelers, nuclear processing (NP), and nuclear transport (NT) proteins. In order to gain a holistic understanding of the non-linear process of transcription, our work examines the communication between all five forementioned classes (or layers) of regulators. We use vastly available rich-media ChIP-chip data for various proteins within the five classes to model a multi-layered transcriptional network of the yeast species Saccharomyces cerevisiae.; (cont.) Following the introduction in Chapter 1...

Semi-supervised learning for natural language

Liang, Percy
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 86 p.; 4273216 bytes; 4277241 bytes; application/pdf; application/pdf
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Statistical supervised learning techniques have been successful for many natural language processing tasks, but they require labeled datasets, which can be expensive to obtain. On the other hand, unlabeled data (raw text) is often available "for free" in large quantities. Unlabeled data has shown promise in improving the performance of a number of tasks, e.g. word sense disambiguation, information extraction, and natural language parsing. In this thesis, we focus on two segmentation tasks, named-entity recognition and Chinese word segmentation. The goal of named-entity recognition is to detect and classify names of people, organizations, and locations in a sentence. The goal of Chinese word segmentation is to find the word boundaries in a sentence that has been written as a string of characters without spaces. Our approach is as follows: In a preprocessing step, we use raw text to cluster words and calculate mutual information statistics. The output of this step is then used as features in a supervised model, specifically a global linear model trained using the Perception algorithm. We also compare Markov and semi-Markov models on the two segmentation tasks. Our results show that features derived from unlabeled data substantially improves performance...

Aircraft position prediction using neural networks

Doshi, Anuja
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 72 leaves; 3878638 bytes; 3881358 bytes; application/pdf; application/pdf
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The Federal Aviation Administration (FAA) has been investigating early warning accident prevention systems in an effort to prevent runway collisions. One system in place is the Airport Movement Area Safety System (AMASS), developed under contract with the FAA. AMASS uses a linear prediction system to predict the position of an aircraft 5 to 30 seconds in the future. The system sounds an alarm to warn air traffic controllers if it foresees a potential accident. However, research done at MIT and Volpe National Transportation Systems Center has shown that neural networks more accurately predict the future position of aircraft. Neural networks are self-learning, and the time required for the optimization of safety logic will be minimized using neural networks. More accurate predictions of aircraft position will deliver earlier warnings to air traffic controllers while reducing the number of nuisance alerts. There are many factors to consider in designing an aircraft position prediction neural network, including history length, types of inputs and outputs, and applicable training data. This document chronicles the design, training, performance, and analysis of a position prediction neural network, and the presents the resulting optimal neural network for the AMASS System. Additionally...

Clock division as a power saving strategy in a system constrained by high transmission frequency and low data rate

Selbst, Andrew D. (Andrew David)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 p.; 2281684 bytes; 2284209 bytes; application/pdf; application/pdf
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Systems are often restricted to have higher transmission frequency than required by their data rates. Possible constraints include channel attenuation, power requirements, and backward compatibility. As a result these systems have unused band- width, leading to inefficient use of power. In this thesis, I propose to slow the internal operating frequency of a cochlear implant receiver in order to reduce the internal power consumption by more than a factor of ten. I have created a new data encoding scheme, called "N-[pi] Shift Encoding", which makes clock division a viable solution. This clock division technique can be applied to other similarly constrained systems.; by Andrew D. Selbst.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; Includes bibliographical references (p. 63).

Implementing rate-distortion optimization on a resource-limited H.264 encoder

Syu, Eric
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 59 leaves; 2165564 bytes; 2167944 bytes; application/pdf; application/pdf
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This thesis models the rate-distortion characteristics of an H.264 video compression encoder to improve its mode decision performance. First, it provides a background to the fundamentals of video compression. Then it describes the problem of estimating rate and distortion of a macroblock given limited computational resources. It derives the macroblock rate and distortion as a function of the residual SAD and H.264 quantization parameter QP. From the resulting equations, this thesis implements and verifies rate-distortion optimization on a resource-limited H.264 encoder. Finally, it explores other avenues of improvement.; by Eric Syu.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; Includes bibliographical references (leaves 57-59).