John D. Hobby

Joint Scheduling and Congestion Control in Mobile Ad-Hoc Networks

In this paper we study the problem of jointly performing scheduling and congestion control in mobile ad-hoc networks so that network queues remain bounded and the resulting flow rates satisfy an associated network utility maximization problem. In recent years a number of papers have presented theoretical solutions to this problem that are based on combining differential-backlog scheduling algorithms with utility-based congestion control. However, this work typically does not address a number of issues such as how signaling should be performed and how the new algorithms interact with other wireless protocols. In this paper we address such issues. In particular: ldr We define a specific network utility maximization problem that we believe is appropriate for mobile adhoc networks. ldr We describe a wireless greedy primal dual (wGPD) algorithm for combined congestion control and scheduling that aims to solve this problem. ldr We show how the wGPD algorithm and its associated signaling can be implemented in practice with minimal disruption to existing wireless protocols. ldr We show via OPNET simulation that wGPD significantly outperforms standard protocols such as 802.11 operating in conjunction with TCP. This work was supported by the DARPA CBMANET program.

Practical segment intersection with finite precision output

Abstract The fundamental problem of finding all intersections among a set of line segments in the plane has numerous important applications. Reliable implementations need to cope with degenerate input and limited precision. Representing intersection points with fixed precision can introduce extraneous intersections. This paper presents simple solutions to these problems and shows that they impose only a very modest performance penalty. Test data came from a data compression problem involving a map database.

Enhancing degraded document images via bitmap clustering and averaging

Proper display and accurate recognition of document images are often hampered by degradations caused by poor scanning or transmission conditions. The authors propose a method to enhance such degraded document images for better display quality and recognition accuracy. The essence of the method is in finding and averaging bitmaps of the same symbol that are scattered across a text page. Outline descriptions of the symbols are then obtained that can be rendered at arbitrary solution. The paper describes details of the algorithm and an experiment to demonstrate its capabilities using fax images.

Matching document images with ground truth

Abstract. Since optical character recognition systems often require very large amounts of training data for optimum performance, it is important to automate the process of finding ground truth character identities for document images. This is done by finding a transformation that matches a scanned image to the machine-readable document description that was used to print the original. Rather than depend on finding feature points, a more robust procedure is to follow up by using an optimization algorithm to refine the transformation. The function to optimize can be based on the character bounding boxes – it is not necessary to have access to the actual character shapes used when printing the original.

The tradeoff between coverage and capacity in dynamic optimization of 3G cellular networks

For 3G cellular networks, capacity is an important objective, along with coverage, when characterizing the performance of high-data-rate services. In live networks, the effective network capacity heavily depends on the degree that the traffic load is balanced over all cells, so changing traffic patterns demand dynamic network reconfiguration to maintain good performance. Using a four-cell sample network, and antenna tilt, cell power level and pilot fraction as adjustment variables, we study the competitive character of network coverage and capacity in such a network optimization process, and how it compares to the CDMA-intrinsic coverage-capacity tradeoff driven by interference. We find that each set of variables provides its distinct coverage-capacity tradeoff behavior with widely varying and application-dependent performance gains. The study shows that the impact of dynamic load balancing highly depends on the choice of the tuning variable as well as the particular tradeoff range of operation.

Rasterization of nonparametric curves

We examine a class of algorithms for rasterizing algebraic curves based on an implicit form that can be evaluated cheaply in integer arithmetic using finite differences. These algorithms run fast and produce “optimal” digital output, where previously known algorithms have had serious limitations. We extend previous work on conic sections to the cubic and higher order curves, and we solve an important undersampling problem.

Analysis and Methodology to Segregate Residential Electricity Consumption in Different Taxonomies

This work presents a two-stage model for the data analysis of electricity consumption. The first stage divides the consumption in two parts: weather- and illumination-related, and residual consumption, where weather-related consumption refers to heating, ventilation, and air conditioning (HVAC). Given the hourly total consumption, we obtain the hourly weather-related and illumination-related electricity consumption, and subtract this out to get residual consumption. The second stage of the model is a flexible, agent-based analytical tool that allows disaggregation of residual consumption into a sum of consumptions by different groups of appliances. This tool can be used for a variety of applications including an optimization of demand-side management and/or a development of a set of desirable patterns for schedules of electricity-related activities in households (within an acceptable range of course) in order to minimize negative effects of high peak demand.

GERI - Bell Labs Smart Grid Research Focus: Economic Modeling, Networking, and Security & Privacy

In this paper, we outline the Grid 2.0 Research, a collaborative Smart Grid research program between Gachon Energy Research Institute (GERI) of Kyungwon University and Bell Labs of Alcatel-Lucent. Salient features of the Grid 2.0 Research are the active role of distributed fixed and mobile energy storage, distributed renewable energy sources, and active load-side participation. Our focus is not on the energy storage itself but rather on the supporting infrastructure including communication network, security, and economics of the Smart Grid. Grid 2.0 Research views the Smart Grid as an ecosystem. In this regard, we pay close attention to the components and systems which require significant fundamental advancement or systems which do not exist today, thus requiring innovative solutions or greater sophistication. In order to realize a functioning ecosystem, critical components and tools of the envisioned Smart Grid are identified. This research work has been motivated by the Smart Grid roadmap of KEPCO and the Jeju Island Smart Grid Test-bed of Korea which will be discussed following the introduction section. Areas of research focus will be explained in a concise manner in the subsequent sections.

Rasterizing curves of constant width

This paper gives a fast, linear-time algorithm for generating high-quality pixel representations of curved lines. The results are similar to what is achieved by selecting a circle whose diameter is the desired line width, and turning on all pixels covered by the circle as it moves along the desired curve. However, the circle is replaced by a carefully chosen polygon whose deviations from the circle represent subpixel corrections designed to improve the aesthetic qualities of the rasterized curve. For nonsquare pixels, equally good results are obtained when an ellipse is used in place of the circle. The class of polygons involved is introduced, an algorithm for generating them is given, and how to construct the set of pixels covered when such a polygon moves along a curve is shown. The results are analyzed in terms of a mathematical model for the uniformity and accuracy of line width in the rasterized image.

Generating automatically tuned bitmaps from outlines

Consider the problem of generating bitmaps from character shapes given as outlines. The obvious scan-conversion process does not produce acceptable results unless important features such as stem widths are carefully controlled during the scan-conversion process. This paper describes a method for automatically extracting the necessary feature information and generating high-quality bitmaps without resorting to hand editing. Almost all of the work is done in a preprocessing step, the result of which is an intermediate form that can be quickly converted into bitmaps once the font size and device resolution are known. A heuristically defined system of linear equations describes how the ideal outlines should be distorted in order to produce the best possible results when scan converted in a straightforward manner. The Lova´sz basis reduction algorithm then reduces the system of equations to a form that makes it easy to find an approximate solution subject to the constraint that some variables must be integers. The heuristic information is of such a general nature that it applies equally well to Roman fonts and Japanese Kanji.