Speech coding is a very important area of research in digital signal processing. It is a fundamental element of digital communications and has progressed at a fast pace in parallel to the increase of demands in telecommunication services and capabilities. Most of the speech coders reported in the literature are based on linear prediction (LP) analysis. Code Excited Linear Predictive (CELP) coder is a typical and popular example of this class of coders. This coder performs LP analysis of speech for extracting LP coefficients and employs an analysis-by-synthesis procedure to search a stochastic codebook to compute the excitation signal. The method used for performing LP analysis plays an important role in the design of a CELP coder. The autocorrelation method is conventionally used for LP analysis. Though this works reasonably well for noise-free (clean) speech, its performance goes down when signal is corrupted by noise. Spectral analysis of speech signals in noisy environments is an aspect of speech coding that deserves more attention. This dissertation studies the application of recently proposed robust LP analysis methods for estimating the power spectrum envelope of speech signals. These methods are the moving average, moving maximum and average threshold methods. The proposed methods will be compared to the more commonly used methods of LP analysis, such as the conventional autocorrelation method and the Spectral Envelope Estimation Vocoder (SEEVOC) method. The Linear Predictive Coding (LPC) spectrum calculated from these proposed methods are shown to be more robust. These methods work as well as the conventional methods when the speech signal is clean or has high signal-to-noise ratio. Also, these robust methods give less quantisation distortion than the conventional methods. The application of these robust methods for speech compression using the CELP coder provides better speech quality when compared to the conventional LP analysis methods.

The protection of digital images and video from unauthorized access is important for a number of applications, including privacy protection in video surveillance and digital rights management for consumer applications. However, traditional cryptographic methods are not well suited to digital visual content. Applying standard encryption approaches to the entire content can require significant computational resources due to the large size of the data. Furthermore, digital images and video often need to be manipulated,such as by resizing or transcoding, which traditional encryption would hinder. A number of image and video-specific encryption approaches have been proposed in the literature, but many of the them have significant negative impact on the ability to compress the data, which is a necessary requirement of most imaging systems. In this work, a secure image coder, called Secure Set Partitioning in Hierarchical Trees (SecSPIHT), is proposed. It combines wavelet-based image coding (compression) with efficient encryption. The encryption is applied to a small number of selected bits in the code domain, to achieve complete confidentiality of all the content while having no negative impact on compression performance. The output of the system is a secure code that cannot be decrypted and decoded without the provision of a secret key. It has superior rate-distortion performance compared to JPEG and JPEG2000, and the bit-rate can be easily scaled via a simple truncation operation. The computational overhead of the encryption operation is very low, typically requiring less than 1% of the coded image data to be encrypted. A related secure object-based coding approach is also presented. Called Secure Shape and Texture Set Partitioning in Hierarchical Trees (SecST-SPIHT), it codes and encrypts arbitrarily-shaped visual objects. A privacy protection system for video surveillance is proposed, using SecST-SPIHT to protect private data, such as face and body images appearing in surveillance footage. During normal operation of the system, the private data objects are protected via SecST-SPIHT. If an incident occurs that requires access to the data (e.g., for investigation), a designated authority must release the key. This is superior to other methods of privacy protection which irreversibly blur or mask the private data.

The protection of digital images and video from unauthorized access is important for a number of applications, including privacy protection in video surveillance and digital rights management for consumer applications. However, traditional cryptographic methods are not well suited to digital visual content. Applying standard encryption approaches to the entire content can require significant computational resources due to the large size of the data. Furthermore, digital images and video often need to be manipulated,such as by resizing or transcoding, which traditional encryption would hinder. A number of image and video-specific encryption approaches have been proposed in the literature, but many of the them have significant negative impact on the ability to compress the data, which is a necessary requirement of most imaging systems. In this work, a secure image coder, called Secure Set Partitioning in Hierarchical Trees (SecSPIHT), is proposed. It combines wavelet-based image coding (compression) with efficient encryption. The encryption is applied to a small number of selected bits in the code domain, to achieve complete confidentiality of all the content while having no negative impact on compression performance. The output of the system is a secure code that cannot be decrypted and decoded without the provision of a secret key. It has superior rate-distortion performance compared to JPEG and JPEG2000, and the bit-rate can be easily scaled via a simple truncation operation. The computational overhead of the encryption operation is very low, typically requiring less than 1% of the coded image data to be encrypted. A related secure object-based coding approach is also presented. Called Secure Shape and Texture Set Partitioning in Hierarchical Trees (SecST-SPIHT), it codes and encrypts arbitrarily-shaped visual objects. A privacy protection system for video surveillance is proposed, using SecST-SPIHT to protect private data, such as face and body images appearing in surveillance footage. During normal operation of the system, the private data objects are protected via SecST-SPIHT. If an incident occurs that requires access to the data (e.g., for investigation), a designated authority must release the key. This is superior to other methods of privacy protection which irreversibly blur or mask the private data.

This thesis studies the applications of the network coding technique for intercon- nect optimization and improving the routability of Very-large-scale integration (VLSI) designs. The goal of the routing process is to connect the required sets of sources and sinks while minimizing the total wirelength and reducing congestion. Typically, chip interconnects include multiple sinks and are routed through intermediate nodes. The main idea of the network coding technique is to enable the intermediate nodes to generate new signals by combining the signals received over their incoming wires. This is in contrast to the traditional approaches, in which an intermediate node can only forward the incoming signals. This thesis attempts to explore the possible ben- efits of the network coding technique for reducing the total wirelengh and mitigating congestion in VLSI designs. The contribution of the thesis is three-fold. First, we extend the Hanan’s theo- rem for multi-net rectilinear coding networks. Second, we propose several exact and heuristic solutions for finding near-optimal routing topologies that utilize network coding techniques. Next, we perform extensive simulation study to evaluate the ad- vantage of network coding over the traditional approaches. The simulations help to identify routing instances where the network coding techniques are expected to be beneficial. Finally, we evaluate the potential benefits from network coding in practical settings by analyzing its performance on the International Symposium on Physical Design (ISPD) benchmarks. Our results show that while network coding shows upto 2.43% improvement on unconstrained rectilinear grids, it shows upto 4.34% improvement in cases with con- straints along the grid. In addition, it shows an improvement upto 8.4% in cases involving congestion reduction and also improves routing performance on ISPD rout- ing benchmarks.

In 1998, J. P. Hansen introduced the construction of an error-correcting code over a finite field Fq from a convex integral polytope in R2. Given a polytope P ⊂ R2, there is an associated toric variety XP , and Hansen used the cohomology and intersection theory of divisors on XP to determine explicit formulas for the dimension and minimum distance of the associated toric code CP . We begin by reviewing the basics of algebraic coding theory and toric varieties and discuss how these areas intertwine with discrete geometry. Our first results characterize certain polygons that generate and do not generate maximum distance separable (MDS) codes and Almost-MDS codes. In 2006, Little and Schenck gave formulas for the minimum distance of certain toric codes corresponding to smooth toric surfaces with rank(Pic(X)) = 2 and rank(Pic(X)) = 3. Additionally, they gave upper and lower bounds on the minimum distance of an arbitrary toric code CP by finding a subpolygon of P with a maximal, nontrivial Minkowski sum decomposition. Following this example, we give explicit formulas for the minimum distance of toric codes associated with two families of smooth toric threefolds with rank(Pic(X)) = 2, characterized by G. Ewald and A. Schmeinck in 1993. Lastly, we give explicit formulas for the dimension of a toric code generated from a Minkowski sum of a finite number of polytopes in R2 and R3 and a lower bound for the minimum distance.

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This dissertation considers three different aspects of modern digital communication systems and is therefore divided in three parts. The first part is distributed coding. This part deals with source and source- channel code design issues for digital communication systems with many transmitters and one receiver or with one transmitter and one receiver but with side information at the receiver, which is not available at the transmitter. Such problems are attracting attention lately, as they constitute a way of extending the classical point-to-point communication theory to networks. In this first part of this dissertation, novel source and source-channel codes are designed by converting each of the considered distributed coding problems into an equivalent classical channel coding or classical source-channel coding problem. The proposed schemes come very close to the theoretical limits and thus, are able to exhibit some of the gains predicted by network information theory. In the other two parts of this dissertation classical point-to-point digital com- munication systems are considered. The second part is quantization of coded chan- nel measurements at the receiver. Quantization is a way to limit the accuracy of continuous-valued measurements so that they can be processed in the digital domain. Depending on the desired type of processing of the quantized data, different quantizer design criteria should be used. In this second part of this dissertation, the quantized received values from the channel are processed by the receiver, which tries to recover the transmitted information. An exhaustive comparison of several quantization cri- teria for this case are studied providing illuminating insight for this quantizer design problem. The third part of this dissertation is faster-than-Nyquist signaling. The Nyquist rate in classical point-to-point bandwidth-limited digital communication systems is considered as the maximum transmission rate or signaling rate and is equal to twice the bandwidth of the channel. In this last part of the dissertation, we question this Nyquist rate limitation by transmitting at higher signaling rates through the same bandwidth. By mitigating the incurred interference due to the faster-than-Nyquist rates, gains over Nyquist rate systems are obtained.

As the rapid evolution of the technology and the network communication, people can share the multimedia content more easily through the Internet. And devices for accessing the Internet include not only the desktop computers but also cell phones, PDAs, and computers on the vehicles. Vehicular ad-hoc networks, which allow mobile users to access the Internet with the computers on cars is one of the most promising technology in the near future. Through VANET, vehicles can not only share the traffic information to avoid accidents, but also exchange the multimedia content through the peer to peer sharing technology. In this thesis we propose using the network coding technology to encode/decode the file blocks in VANET, clustering the vehicles according to their mobility, and combining the ROMSGP and modifying the priority method of the VANETCODE scheme in order to enhance the overall performance of VANETs.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (p. 73-78).

Thesis (Ph.D.)--University of Texas at Arlington, 2008.