Robert Benkoczi

Channel Assignment for Multihop Cellular Networks: Minimum Delay

Multihop cellular networks (MCNs) enhance the capacity and coverage and alleviate the dead-spot and hot-spot problems of cellular networks. They also allow faster and cheaper deployment of cellular networks. A fundamental issue of these networks is packet delay because multihop relaying for signals is involved. An effective channel assignment is the key to reducing delay. In this paper, we propose an optimal and a heuristic channel assignment scheme, called OCA and minimum slot waiting first (MSWF), respectively, for a time division duplex (TDD) wideband code division multiple access (W-CDMA) MCN. OCA provides an optimal solution in minimizing packet delay and can be used as an unbiased or benchmark tool for comparison among different network conditions or networking schemes. However, OCA is computationally expensive and, thus, inefficient for large real-time channel assignment problem. In this case, MSWF is more appropriate. Simulation results show that MSWF achieves on average 95 percent of the delay performance of OCA and is effective in achieving high throughput and low packet delay in conditions of different cell sizes.

Routing and link scheduling with QoS in IEEE 802.16 mesh networks

Quality of service (QoS) in wireless mesh networks is an active area of research which is driven by the increasing demand for multimedia content delivered wirelessly. The IEEE 802.16 (WiMAX) standard identifies four classes of service targeting throughput, delay, and jitter. In this paper, we achieve two main objectives. (1) We present a routing metric sensitive to both interference and throughput which proves effective in QoS provisioning, a link scheduling algorithm that can easily accommodate all four classes of service by using the concept of feasible intervals, and an effective channel allocation algorithm inspired by a constraint programming heuristic. (2) We prove that the usual approach of constructing routing trees centred at the base station could lock significant network resources. By simply switching to a session based routing strategy, we illustrate that the acceptance ratio under a congested network can improve by more than 10% when compared to the tree based routing driven by our interference and throughput aware metric and by more than 25% when the routing tree is constructed with the metric sensitive to interference only.

Towards Global Connectivity by Joint Routing and Scheduling in Wireless Mesh Networks

Wireless mesh networks are at the forefront of the technological drive. Achieving high system throughput in these networks is challenging due to interference which limits concurrent transmissions. In this paper we study routing and link scheduling in time division multiple access networks free of contention. We extend the work in the literature in several ways: (a) we present simple joint routing and time slot scheduling algorithms that have outperformed the existing proposals in most of our experiments, (b) we report the results using a simple combinatorial bound on the optimal routing/scheduling solution which gives us an absolute measure of the quality of the routes, (c) we depart from the classical routing tree approach by constructing session based routes for data and we quantify the performance gains for this approach to justify its use when QoS constraints are considered. We perform extensive experiments to evaluate our model. Results from the experiments indicate that our model outperforms most of the known approaches in the literature.

New Upper Bounds on Continuous Tree Edge-Partition Problem

We consider continuous tree edge-partition problem on a edge-weighted tree network. A continuous p-edge-partition of a tree is to divide it into psubtrees by selecting p? 1 cut points along the edges of the underlying tree. The objective is to maximize (minimize) the minimum (maximum) length of the subtrees. We present an O(nlog2n)-time algorithm for the max-min problem which is based on parametric search technique [7] and an efficient solution to the ratio search problem. Similar algorithmic technique, when applied to the min-max problem, results in an O(nh T logn)-time algorithm where h T is the height of the underlying tree network. The previous results for both max-min and min-max problems are O(n2) [5].

Resource assignment in vehicular clouds

We study the task scheduling problem in vehicular clouds. Task scheduling in vehicular clouds must deal with the transient nature of the cloud resources and a relaxed definition of non-preemptive tasks. Despite a rich literature in machine scheduling and grid computing, this problem has not been examined yet. We show that even the problem of finding a minimum cost schedule for a single task over unrelated machines is NP-hard. We then provide a fully polynomial time approximation scheme and a greedy approximation for scheduling a single task. We extend these algorithms to the case of scheduling n tasks. We validate our algorithms through extensive simulations that use synthetically generated data as well as real data extracted from vehicle mobility and grid computing workload traces. Our contributions are, to the best of our knowledge, the first quantitative analysis of the computational power of vehicular clouds.

Minimizing Total Sensor Movement for Barrier Coverage by Non-uniform Sensors on a Line

Barrier coverage is a cost effective approach for intruder detection applications. It relies on monitoring the perimeter, or barrier, around the area of interest by placing sensors at appropriate locations on the barrier. In this paper we consider the problem of barrier coverage of a line segment by moving sensors along the line containing the segment. We extend the results existing in the literature by considering the case of non-uniform sensors placed at initial positions that do not overlap with the interval of interest.

Mesh Network Deployment to Ensure Global Reachability

We propose and study a network design problem whose goal is to ensure Internet reach ability to mobile wireless devices. Such design of networks is a resource location allocation problem related to minimum cost unsplitable flow in a tripartite network. We present IP formulation for the problem, and produce test results with ILOG CPLEX. We also present heuristic algorithms using local search and VNS based procedures. We test the algorithms with different randomly generated network instances from size 500 - 5000 nodes. Our algorithms could obtain optimal solution for some of the input instances, beat the solutions obtained by CPLEX for some others, and obtained a worst case integrality gap of 3% for the rest.

An evolutionary approach to planning IEEE 802.16 networks

Efficient and effective deployment of IEEE 802.16 networks to service an area of users with certain traffic demands is an important network planning problem. We resort to an evolutionary approach in order to yield good approximation solutions. In our method, novel genetic variation operations are proposed to incorporate the feature of this real-world application of evolutionary algorithm.

A design structure matrix approach for measuring co-change-modularity of software products

Several authors have quantified the modularity of software systems in terms of coupling and cohesion metrics. Most of these approaches focus on functional and procedural dependencies in the system. Although highly relevant at the design phase, these static dependencies alone do not account for how a software product evolves over time. Instead, this is also dictated by logical and hidden dependencies between system files. To a large extent, the co-change (co-commit) relation captures these different types of dependencies. In this paper, we define two measures of co-change-modularity of a software product based on a weighted design structure matrix (DSM). The first metric, called the weighted propagation cost, uses matrix exponential to measure how changes to one system file potentially affect the whole product. The second metric, called the weighted clustering cost, uses the output of the first metric to measure the partitionability of the system based on the co-change relation. In addition, we provide a visual representation of how the co-change structure of a system evolves over time. We discuss the theoretical foundation of our work and highlight its advantages over existing methodologies. We apply our approach to GNU Octave and show the findings to be consistent with the available literature on the evolution of Octave. Our analysis is extensible and applicable to a range of scenarios including open source systems.

Minsum k-Sink Problem on Dynamic Flow Path Networks

In emergencies such as earthquakes, nuclear accidents, etc., we need an evacuation plan. We model a street, a building corridor, etc. by a path network, and consider the problem of locating a set of k sinks on a dynamic flow path network with n vertices, where people are located, that minimizes the sum of the evacuation times of all evacuees. Our minsum model is more difficult to deal with than the minmax model, because the cost function is not monotone along the path. We present an \(O(kn^2\log ^2 n)\) time algorithm for solving this problem, which is the first polynomial time result. If the edge capacities are uniform, we give an \(O(kn\log ^3 n)\) time algorithm.