Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

Browse

Search Results

Now showing 1 - 10 of 228
  • Thumbnail Image
    Item
    Distributed Topology Control for Stable Path Routing in Mobile Ad Hoc Networks
    (2009-12-09) Somasundaram, Kiran K.; Jain, Kaustubh; Tabatabaee, Vahid; Baras, John S.
    In this paper, we introduce the stable path topology control problem for routing in Mobile Ad Hoc Networks (MANETs). We formulate the problem as a constrained multiagent optimization problem with only local neighborhood information. We develop and prove local pruning strategies that solve this problem. We also introduce the notion of distorted pruning, which offers a systematic method to trade path stability off against the hop count metric. Finally, we quantify the performance of our pruning algorithms using several simulation scenarios.
  • Thumbnail Image
    Item
    Component Based Performance Modelling of the Wireless Routing Protocols
    (2008) Tabatabaee, Vahid; Baras, John S.; Purkayastha, Punyaslok; Somasundaram, Kiran
    In this paper, we propose a component based methodology for modelling and design of wireless routing protocols. Componentization is a standard methodology for analysis and synthesis of complex systems. Throughout the paper, we use Optimized Link State Routing (OLSR) protocol as a case study to demonstrate effectiveness of our methodology. We focus on modelling of three main components: neighborhood discovery, selector of topology information to disseminate, and the path selection components. For each component, we identify the inputs, outputs, and a generic methodology for modelling. Using the neighborhood discovery component, we will present our design methodology and design a modified enhanced version of the OLSR NDC, and compare its performance to the neighborhood discovery component of the OLSR protocol.
  • Thumbnail Image
    Item
    Performance Metric Sensitivity Computation for Optimization and Trade-off Analysis in Wireless Networks
    (2008-02-26) Baras, John S.; Tabatabaee, Vahid; Papageorgiou, George; Rentz, Nicolas
    We develop and evaluate a new method for estimating and optimizing various performance metrics for multi-hop wireless networks, including MANETs. We introduce an approximate (throughput) loss model that couples the physical, MAC and routing layers effects. The model provides quantitative statistical relations between the loss parameters that are used to characterize multiuser interference and physical path conditions on the one hand and the traffic rates between origin-destination pairs on the other. The model takes into account effects of the hidden nodes, scheduling algorithms, IEEE 802.11 MAC and PHY layer transmission failures and finite packet transmission retries at the MAC layer in arbitrary network topologies where multiple paths share nodes. We apply Automatic Differentiation (AD) to these implicit performance models, and develop a methodology for sensitivity analysis, parameter optimization and trade-off analysis for key wireless protocols. Finally, we provide simulation experiments to evaluate the effectiveness and performance estimation accuracy of the proposed models and methodologies.
  • Thumbnail Image
    Item
    Convergence Results for Ant Routing Algorithms via Stochastic Approximation and Optimization
    (2007) Purkayastha, Punyaslok; Baras, John S.
    ``Ant algorithms'' have been proposed to solve a variety of problems arising in optimization and distributed control. They form a subset of the larger class of ``Swarm Intelligence'' algorithms. The central idea is that a "swarm" of relatively simple agents can interact through simple mechanisms and collectively solve complex problems. Instances that exemplify the above idea abound in nature. The abilities of ant colonies to collectively accomplish complex tasks have served as sources of inspiration for the design of ``Ant algorithms''. Examples of ``Ant algorithms'' are the set of ``Ant Routing'' algorithms that have been proposed for communication networks. We analyze in this paper Ant Routing Algorithms for packet-switched wireline networks. The algorithm retains most of the salient and attractive features of Ant Routing Algorithms. The scheme is a multiple path probabilistic routing scheme, that is fully adaptive and distributed. Using methods from adaptive algorithms and stochastic approximation, we show that the evolution of the link delay estimates can be closely tracked by a deterministic ODE system. A study of the equilibrium points of the ODE gives us the equilibrium behavior of the routing algorithm, in particular, the equilibrium routing probabilities, and mean delays in the links under equilibrium. We also show that the fixed-point equations that the equilibrium routing probabilities satisfy are actually the necessary and sufficient conditions of an appropriate optimization problem. Simulations supporting the analytical results are provided.
  • Thumbnail Image
    Item
    Sensor scheduling using smart sensors
    (2007) Hovareshti, Pedram; Gupta, Vijay; Baras, John S.
    The sensor selection problem arises when multiple sensors are jointly trying to estimate a process but only a subset of them can take and/or use measurements at any time step. In a networked estimation situation, sensors are typically equipped with some memory and processing capabilities. We illustrate that utilization of these capabilities can lead to significant performance gains in the sensor selection problem for improved inference. Further, it also leads to significant pruning of the search tree that yields the optimum sensor schedule. We also present a periodicity result for the case where the decision is whether the sensor should transmit or not.
  • Thumbnail Image
    Item
    Optimal Output Feedback Control Using Two Remote Sensors over Erasure Channels
    (2007) Gupta, Vijay; Martins, Nuno C.; Baras, John S.; Martins, Nuno C.; ISR
  • Thumbnail Image
    Item
    Broadcast Scheduling for Push Broadcast Systems with Arbitrary Cost Functions
    (2007) Raissi-Dehkordi, Majid; Baras, John S.; ISR
    In this report the problem of broadcast scheduling in Push broadcast systems is studied. We introduce an optimization approach that leads to well justified policies for Push broadcast systems with generalized cost functions. In particular, we apply our results to a Push broadcast system with different deadlines associated to the files while allowing the files to have unequal demand rates and lengths. We will show that our proposed policy covers some of the previously investigated Push systems as special cases and is applicable to a wide range of cost functions assigned to the files. We also calculate the optimal average cost for our experimental settings and show, through extensive simulation studies, that our results closely match that value for each experiment.
  • Thumbnail Image
    Item
    New Algorithms for the Efficient Design of Topology-Oriented Key Agreement Protocols in Multi-Hop Ad Hoc Networks
    (2006) Striki, Maria; Baras, John S.; Manousakis, Kyriakos; ISR; CSHCN
    Securing group communications in resource constrained, infrastructure-less environments such as Mobile Ad Hoc Networks (MANETs) has become one of the most challenging research directions in the areas of wireless network security. MANETs are emerging as the desired environment for an increasing number of commercial and military applications, addressing also an increasing number of users. Security on the other hand, is becoming an indispensable requirement of our modern life for all these applications.

    The inherent limitations of such dynamic and resource-constraint networks impose major difficulties in establishing a suitable secure group communications framework. This is even more so for the operation of Key Agreement (KA), under which all parties contribute equally to the group key. The logical design of efficient KA protocols has been the main focus of the related research to-date. Such a consideration however, gives only a partial account on the feasibility and actual performance of a KA protocol in a real multi-hop network. This is because protocols have been evaluated only in terms of the group key related messaging in isolation from the underlying network functions that interact with the logical scheme and support its correct execution (i.e. routing).

    In this work, we contribute towards efficiently extending a number of Diffie-Hellman (DH)-based group KA protocols in wireless multi-hop ad hoc networks, and measuring their actual performance over these networks. Towards this end, we introduce a number of new algorithms and techniques that aim in efficiently merging the logical design of KA protocols with the underlying routing and topology of the network, to produce protocols that substantially improve one or more metrics of interest. Indeed, the resulting protocols are significantly more efficient in some or all of the above metrics, as our analytical and simulation results indicate.

  • Thumbnail Image
    Item
    Efficient sampling for keeping track of an Ornstein-Uhlenbeck process
    (2006) Rabi, Maben; Moustakides, George; Baras, John S.; Baras, John S.; ISR; SEIL
    We consider estimation and tracking problems in sensor networks with constraints in the hierarchy of inference making, on the sharing of data and inter-sensor communications. We identify as a typical representative for such problems tracking of a process when the number and type of measurements in constrained. As the simplest representative of such problems, which still encompasses all the key issues involved we analyze efficient sampling schemes for tracking an Ornstein-Uhlenbeck process. We considered sampling based on time, based on amplitude (event-triggered sampling) and optimal sampling (optimal stopping). We obtained the solution in each case as a constrained optimization problem. We compare the performance of the various sampling schemes and show that the event-triggered sampling performs close to optimal. Implications and extensions are discussed.
  • Thumbnail Image
    Item
    Consensus Problems on Small World Graphs: A Structural Study
    (2006) Hovareshti, Pedram; Baras, John S.; Baras, John S.; ISR; CSHCN