We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

We propose a natural scene statistic-based distortion-generic blind/no-reference (NR) image quality assessment (IQA) model that operates in the spatial domain. The new model, dubbed blind/referenceless image spatial quality evaluator (BRISQUE) does not compute distortion-specific features, such as ringing, blur, or blocking, but instead uses scene statistics of locally normalized luminance coefficients to quantify possible losses of “naturalness” in the image due to the presence of distortions, thereby leading to a holistic measure of quality. The underlying features used derive from the empirical distribution of locally normalized luminances and products of locally normalized luminances under a spatial natural scene statistic model. No transformation to another coordinate frame (DCT, wavelet, etc.) is required, distinguishing it from prior NR IQA approaches. Despite its simplicity, we are able to show that BRISQUE is statistically better than the full-reference peak signal-to-noise ratio and the structural similarity index, and is highly competitive with respect to all present-day distortion-generic NR IQA algorithms. BRISQUE has very low computational complexity, making it well suited for real time applications. BRISQUE features may be used for distortion-identification as well. To illustrate a new practical application of BRISQUE, we describe how a nonblind image denoising algorithm can be augmented with BRISQUE in order to perform blind image denoising. Results show that BRISQUE augmentation leads to performance improvements over state-of-the-art methods. A software release of BRISQUE is available online: http://live.ece.utexas.edu/research/quality/BRISQUE_release.zip for public use and evaluation.

/pdf/no-reference-image-quality-assessment-in-the-spatial-domain-2mnlvf25ig.pdf

No-Reference Image Quality Assessment in the Spatial Domain

An important aim of research on the blind image quality assessment (IQA) problem is to devise perceptual models that can predict the quality of distorted images with as little prior knowledge of the images or their distortions as possible. Current state-of-the-art “general purpose” no reference (NR) IQA algorithms require knowledge about anticipated distortions in the form of training examples and corresponding human opinion scores. However we have recently derived a blind IQA model that only makes use of measurable deviations from statistical regularities observed in natural images, without training on human-rated distorted images, and, indeed without any exposure to distorted images. Thus, it is “completely blind.” The new IQA model, which we call the Natural Image Quality Evaluator (NIQE) is based on the construction of a “quality aware” collection of statistical features based on a simple and successful space domain natural scene statistic (NSS) model. These features are derived from a corpus of natural, undistorted images. Experimental results show that the new index delivers performance comparable to top performing NR IQA models that require training on large databases of human opinions of distorted images. A software release is available at http://live.ece.utexas.edu/research/quality/niqe_release.zip.

/pdf/making-a-completely-blind-image-quality-analyzer-4rsald8tn3.pdf

Making a “Completely Blind” Image Quality Analyzer

Over the past decade, there has been an explosion of interest in network research across the physical and social sciences. For social scientists, the theory of networks has been a gold mine, yielding explanations for social phenomena in a wide variety of disciplines from psychology to economics. Here, we review the kinds of things that social scientists have tried to explain using social network analysis and provide a nutshell description of the basic assumptions, goals, and explanatory mechanisms prevalent in the field. We hope to contribute to a dialogue among researchers from across the physical and social sciences who share a common interest in understanding the antecedents and consequences of network phenomena.

/pdf/network-analysis-in-the-social-sciences-440fzedv4c.pdf

Network Analysis in the Social Sciences

I. the origin of species by means of natural selection

The authors investigate burst-level bandwidth reservation schemes in ATM LANs and compare the performance of REQ/ACK and on-the-fly reservation schemes for a client-server model with a single ATM switch. To compare performance, they derive an analytical model for the mean burst transfer delay, blocking probability and throughput. They discuss the dependence of these performance parameters on the propagation delay-to-burst duration ratio and peak rate-to-link speed ratio. They show that, for moderate propagation delay-to-burst duration ratio, the on-the-fly scheme is more desirable since the REQ/ACK scheme has limited achievable throughput for fast reservation traffic due to unused bandwidth during the REQ-ACK cycle. Also, for a given burst length (in bits), the delay performance of REQ/ACK scheme is more sensitive to increase in the peak rate than the on-the-fly scheme. >

Performance of burst-level bandwidth reservation in ATM LANs

Through comprehensive simulation studies, we have evaluated the ATM layer end-to-end performance of a constant bit rate (CBR) MPEG2 connection. For most practical cases that we have considered, a cell delay variation (CDV) value of 160 /spl mu/sec is obtained (using 155 Mbps OC-3 rate), well below the 1 msec worst case stated in prior studies. The results also indicate that the uniform distribution proposed in the ATM Forum provides a pessimistic model for the cell delay variation. We demonstrate that a gamma distribution adequately models the cell delay and delay variation (CDV). We also study the effect of various network/source parameters (such as the background load, the number of background sources, the number of hops, and the link-speed) on the variances of CDV and the end-to-end delay of the reference connection. Finally, we examine the variation in the cell delay correlation of a reference connection with the above parameters. We show that the correlation is a decreasing non-periodic/periodic function if the reference CBR is multiplexed with the same/other classes of CBR connections.

A simulation study of delay and delay variation in ATM networks .I. CBR traffic

This paper looks at the problem of traffic engineering and network control from a new perspective. A graph-theoretical metric, betweenness, in combination with a network weight matrix is used to characterize the robustness of a network. Theoretical results lead to a definition of ”criticality” for nodes and links. It is shown that this quantity is a global network quantity and depends on the weight matrix of the graph. Strict convexity of network criticality is proved and an optimization problem is solved to minimize the network criticality as a function of weight matrix which in turn provides maximum robustness. Investigation of the condition of optimality suggests directions to design appropriate control laws and traffic engineering methods to robustly assign traffic flows. The choice of the path for routing the flow in these traffic engineering methods is in the direction of preserving the robustness of the network to the unforeseen changes in topology and traffic demands. The proposed method is useful in situations like MPLS and Ethernet networks where path assignment is required.

A graph theoretical approach to traffic engineering and network control problem

This paper reports on a probabilistic method for traffic engineering (specifically routing and resource allocation) in backbone networks, where the transport is the main service and robustness to the unexpected changes in network parameters is required. We analyze the network using the probabilistic betweenness of the network nodes (or links). The theoretical results lead to the definition of "criticality" for nodes and links. Link criticality is used as the main metric to model the risk of taking a specific path from a source to a destination node. Different paths will be ranked based on their criticality measure, and the best path will be selected to route the flow along the core network. The choice of the path is in the direction of preserving the robustness of the network to the unforeseen changes in topology and traffic demands. The proposed method is useful in situations like MPLS and Ethernet networks where path assignment is required.

Alberto Leon-Garcia

Papers

Performance of burst-level bandwidth reservation in ATM LANs

A simulation study of delay and delay variation in ATM networks .I. CBR traffic

A graph theoretical approach to traffic engineering and network control problem

On Robust Traffic Engineering in Transport Networks

Performance analysis of an integrated hybrid-switched multiplex structure