Ajay K. Gupta

Opportunistic Networks for Emergency Applications and Their Standard Implementation Framework

We present a novel paradigm of opportunistic networks or oppnets in the context of emergency preparedness and response (EPR). Oppnets constitute the category of ad hoc networks where diverse systems, not employed originally as nodes of an oppnet, join it dynamically in order to perform certain tasks they have been called to participate in. After describing the oppnets and their operation, we discuss the oppnet virtual machine (OVM) - a standard implementation framework for oppnet applications. Oppnets can significantly improve effectiveness and efficiency of EPR one of the six mission areas within the national strategy for homeland security. They can also improve other diverse applications, including agriculture, environment, healthcare, manufacturing, surveillance, and transportation. Oppnets should create new application niches as yet hard to imagine. To the best of our knowledge we have been the first to work on oppnets.

Workforce‐constrained Preventive Maintenance Scheduling Using Evolution Strategies

Heavy equipment overhaul facilities such as aircraft service centers and railroad yards face the challenge of minimizing the makespan for a set of preventive maintenance (PM) tasks, requiring single or multiple skills, within workforce availability constraints. In this paper, we examine the utility of evolution strategies to this problem. Comparison of the computational efforts of evolution strategies with exhaustive enumeration to reach optimal solutions for 60 small problems illustrates the ability of evolution strategies to yield optimal solutions increasingly efficiently with increasing problem size. A set of 852 large-scale problems was solved using evolution strategies to examine the effects of task-related problem characteristics, workforce-related variables, and evolution strategies population size (μ) on CPU time. The results empirically supported practical utility of evolution strategies to solve large-scale, complex preventive maintenance problems involving single- and multiple-skilled workforce. Finally, comparison of evolution strategies and simulated annealing for the 852 experiments indicated much faster convergence to optimality with evolution strategies.

The Concept of Opportunistic Networks and their Research Challenges in Privacy and Security

Critical privacy and security challenges confront all researchers and developers working on ever more pervasive computing systems. We belong to this group. We proposed a new paradigm and a new technology of opportunistic networks or oppnets to enable integration of the diverse communication, computation, sensing, storage and other devices and resources that surround us more and more. We not only find ourselves in their midst but depend on them increasingly as necessities rather than luxuries. As communications and computing systems are becoming more and more pervasive, the related privacy and security challenges become tougher and tougher. With oppnets, we charted a new direction within the area of computer networks. One of us invented opportunistic sensor networks [3]. The idea was later generalized by two of us to general opportunistic networks1 [31]. To the best of our knowledge we are now the first to scrutinize privacy and security challenges inherent in oppnets.

Incomplete hypercubes: algorithms and embeddings

The hypercube, though a popular and versatile architecture, has a major drawback in that its size must be a power of two. In order to alleviate this drawback, Katseff [1988] defined theincomplete hypercube, which allows a hypercube-like architecture to be defined for any number of nodes. In this paper we generalize this definition and introduce the namecomposite hypercube. The main result of our work shows that these incomplete architectures can be used effectively and without the size penalty. In particular, we show how to efficiently implement Fully Normal Algorithms on composite hypercubes. Development of these types of algorithms on composite hypercubes allows us to efficiently execute several algorithms concurrently on a complete hypercube. We also show that many host architectures, such as binary trees, arrays and butterflies, can be optimally embedded into composite hypercubes. These results imply that algorithms originally designed for any such host can be optimally mapped to composite hypercubes. Finally, we show that composite hypercubes exhibit many graph theoretic properties that are common with complete hypercubes. We also present results on efficient representations of composite hypercubes within a complete hypercube. These results are crucial in task allocation and job scheduling problems.

Opportunistic Networks: Challenges in Specializing the P2P Paradigm

We introduce the notion of opportunistic networks or oppnets, some of which can be considered a subclass of the peer-to-peer (P2P) networks. Initially, a relatively small seed oppnet is deployed, which grows into a bigger expanded oppnet. Oppnet growth starts with detecting diverse systems existing in its relative vicinity. Systems with best evaluations are invited by an oppnet to become its helpers. The oppnet leverages vast collective capabilities and resources of its helpers, employing them to execute diverse tasks in support of its goals. Though oppnet characteristics make them a natural fit for emergency response applications, we expect that they will prove beneficial in many other application areas. We discuss challenges in the development and use of the oppnet technology. Oppnets that use P2P interactions can be viewed as a specialization of the more general paradigm of P2P networks. To the best of our knowledge, we were the first to define and are now the first to investigate oppnets

Embedding complete binary trees into butterfly networks

The authors present embeddings of complete binary trees into butterfly networks with or without wrap-around connections. Let m be an even integer and q=m+(log m)-1. The authors show how to embed a 2/sup q+1/-1-node complete binary tree T(q) into a (m+1)2/sup m+1/-node wrap-around butterfly B/sub w/(m+1) with a dilation of 4, and how to embed T(q) into a (m+2)2/sup m+2/-node wrap-around butterfly B/sub w/(m+2) with an optimal dilation of 2. They also present an embedding of a wrap-around butterfly B/sub w/(m) into a (m+1)2/sup m/-node no-wrap-around butterfly B(m) with a dilation of 3. Using this embedding it is shown that T(q) can be embedded into a no-wrap butterfly B(m+1) (resp. B(m+2)) with a dilation of 8 (resp. 5). >

Opportunistic resource utilization networks-A new paradigm for specialized ad hoc networks

We present opportunistic resource utilization networks or oppnets, a novel paradigm of specialized ad hoc networks. We believe that applications can benefit from using specialized ad hoc networks that provide a natural basis for them, the basis more efficient and effective than what general-purpose ad hoc networks can offer. Oppnets constitute the subcategory of ad hoc networks where diverse systems, not employed originally as nodes of an oppnet, join it dynamically in order to perform certain tasks they have been called to participate in. Oppnets have a significant potential to improve a variety of applications, and to create new application niches. We categorize opportunistic networks currently known in the literature as class 1opportunistic networks that use opportunistically only communication resources, and class 2opportunistic networks or oppnets that use opportunistically all kinds of resources, including not only communication but also computation, sensing, actuation, storage, etc. After describing the oppnets and the basics of their operation, we discuss the Oppnet Virtual Machine (OVM)-a proposed standard implementation framework for oppnet applications. It is followed by a discussion of an example application scenario using the OVM primitives. Next, we discuss the design and operations of a small-scale oppnet, named MicroOppnet, originally developed as a proof of concept. MicroOppnet is now being extended to serve as a testbed for experimentation and pilot implementations of oppnet architectures and their components. We conclude with a summary and a list of some open issues for oppnets.

Measurement and Reduction of ISI in High-Dynamic-Range 1-bit Signal Generation

This paper studies spurious signals produced by the nonlinear interaction of the previous output symbols of a digital-to-analog converter (DAC) with its current symbol. This effect, called nonlinear intersymbol interference (ISI), significantly degrades the spurious-free dynamic range of most high-speed DACs. Many papers have been devoted to suppressing level inaccuracies in multibit DACs. However, even when all levels are accurate, nonlinear ISI causes significant spurious output. This paper presents a simple and very general model for nonlinear ISI and uses it to design binary signals that can both measure and suppress the spurious tones that arise in a single-bit DAC. While the analysis in this paper is based on a 1-bit DAC, extension to multibit DACs is possible, since a multibit DAC is merely a collection of 1-bit DACs and exhibits the same nonlinear effects. Experimental verification is presented for three different hardware setups. Measurements first establish the presence of the spurious tones in the hardware, as predicted by the model, and then show how the spur level can be reduced by as much as 22 dB.

Efficient embeddings of ternary trees into hypercubes

In this paper we present efficient graph embeddings for complete k-ary trees into boolean hypercubes. In particular, we describe an efficient embedding of a complete ternary tree (k = 3) of height h into a hypercube, which achieves dilation 3 and expansion Θ(1.0104...h). The previously best-known result is dilation 2 and expansion Θ(1.333...h). Our embedding achieves exponentially better expansion at the cost of an increase of 1 in the dilation. We also describe efficient embeddings of k-ary trees into hypercubes when k = 2p * 3q for some p, q > 0 such that the embeddings achieve small constant dilation.

Latin cubes and parallel array access

The problem of efficiently storing a d-dimensional array into multiple memory modules of a shared memory machine is an important problem in parallel processing. We consider the problem for the three-dimensional arrays. More specifically, given an array A of size n/spl times/n/spl times/n and a shared memory machine with n memory modules, we show how to store A so that no two elements within any row, any column, any diagonal of a face of A and main sub-arrays of A are stored in the same memory module. The scheme thus achieves no memory conflicts when the processors of the shared memory machine simultaneously access elements within a row, column, sub-array. etc. We also show how to store A efficiently, if diagonals of A are required to be accessed conflict-free in addition to rows and columns. All of the schemes use latin cubes.<<ETX>>