http://hdl.handle.net/1903/4376 2013-05-22T22:34:37Z 2013-05-22T22:34:37Z Jain, Kaustubh Baras, John S. http://hdl.handle.net/1903/13859 2013-04-09T02:32:47Z 2013-04-01T00:00:00Z

Title: Modeling the Impact of Protocols on Traffic Burstiness At Large Timescales in Wireless Multi-Hop Networks Authors: Jain, Kaustubh; Baras, John S. Abstract: We investigate the impact of the protocol stack on traffic burstiness at large time-scales in wireless multi-hop network traffic. Origins of traffic burstiness at large scales (like its LRD nature) have been mostly attributed to the heavy-tails in traffic sources. In wired networks, protocol dynamics have little impact on large time-scale dynamics. However, given the nature of wireless networks, the MAC and routing layers together can lead to route flapping or oscillations even in a static network. Hence, we explore whether these dynamics can lead to traffic burstiness and LRD. Using network simulations, we analyze traffic for two MANET routing protocols - OLSR and AODV. By varying the routing protocol parameters, we analyze their role in inducing or preventing route oscillations, and study their impact on traffic LRD. We find that, losses in OLSR control packets, due to congestion at the MAC, can lead to route oscillations and traffic burstiness at large timescales. By tuning the parameters, route oscillations and traffic LRD can be avoided. AODV dynamics show little evidence for traffic LRD, even though we cannot rule out this possibility. We also show that the route oscillations can have heavier body and tail than exponential distribution, and that the Markovian framework for route oscillations is inadequate to explain the observed traffic scaling. Lastly, we give a model that captures the MAC and OLSR routing protocol interactions and depending upon chosen protocol parameters and input load, correctly predicts the presence of traffic LRD. Thus, we use this model to design appropriate choice of protocol parameters to mitigate traffic burstiness at large-timescales.

2013-04-01T00:00:00Z Chen, Hua Baras, John http://hdl.handle.net/1903/13857 2013-04-24T13:54:26Z 2013-01-01T00:00:00Z

Title: Distributed Opportunistic Scheduling for Wireless Ad-Hoc Networks with Block-Fading Model Authors: Chen, Hua; Baras, John Abstract: In this paper, we study a distributed opportunistic scheduling problem to exploit the channel fluctuations in wireless ad-hoc networks. In this problem, channel probing is followed by a transmission scheduling procedure executed independently within each link in the network. We study this problem for the popular block-fading channel model, where channel dependencies are inevitable between different time instances during the channel probing phase. Different from existing works, we explicitly consider this type of channel dependencies and its impact on the transmission scheduling and hence the system performance. We use optimal stopping theory to formulate this problem, but at carefully chosen time instances at which effective decisions are made. The problem can then be solved by a new stopping rule problem where the observations are independent between different time instances. Since the stopping rule problem has an implicit horizon determined by the network size, we first characterize the system performance using backward induction. We develop one recursive approach to solve the problem and show that the computational complexity is linear with respect to network size. Due to its computational complexity, we present an approximated approach for performance analysis and develop a metric to check how good the approximation is. We characterize the achievable system performance if we ignore the finite horizon constraint and design stopping rules based on the infinite horizon analysis nevertheless. We present an improved protocol to reduce the probing costs which requires no additional cost. We characterize the performance improvement and the energy savings in terms of the probing signals. We show numerical results based on our mathematical analysis with various settings of parameters.

2013-01-01T00:00:00Z Delgoshaei, Parastoo http://hdl.handle.net/1903/13713 2013-03-26T02:31:10Z 2012-12-18T00:00:00Z

Title: ONTOLOGY-ENABLED TRACEABILITY MODELS FOR ENGINEERING SYSTEMS DESIGN AND MANAGEMENT Authors: Delgoshaei, Parastoo Abstract: This thesis describes new models and a system for satisfying requirements, and an architectural framework for linking discipline-specific dependencies through inter- action relationships at the ontology (or meta-model) level. In a departure from state-of-the-art traceability mechanisms, we ask the question: What design concept (or family of design concepts) should be applied to satisfy this requirement? Solu- tions to this question establish links between requirements and design concepts. The implementation of these concepts leads to the design itself. These ideas, and support for design-rule checking are prototyped through a series of progressively complicated applications, culminating in a case study for rail transit systems management.

2012-12-18T00:00:00Z Herrmann, Jeffrey http://hdl.handle.net/1903/13711 2013-03-23T02:31:15Z 2013-03-01T00:00:00Z

Title: Scheduling Perfectly Periodic Services Quickly with Aggregation Authors: Herrmann, Jeffrey Abstract: The problem of scheduling periodic services that have different period lengths seeks to find a schedule in which the workload is nearly the same in every time unit. A time unit’s workload is the sum of the workloads of the services scheduled for that time unit. A level workload minimizes the variability in the resources required and simplifies capacity and production planning. This paper considers the problem in which the schedule for each service must be perfectly periodic, and the schedule length is a multiple of the services’ period lengths. The objective is to minimize the maximum workload. The problem is strongly NP-hard, but there exist heuristics that perform well when the number of services is large. Because many services will have the same period length, we developed a new aggregation approach that separates the problem into subproblems for each period length, uses the subproblem solutions to form aggregate services, schedules these, and then creates a solution to the original instance. We also developed an approach that separates the problem into subproblems based on a partition of the period lengths. Computational experiments show that using aggregation generates high-quality solutions and reduces computational effort. The quality of the partition approach depended upon the partition used.

2013-03-01T00:00:00Z