Sami J. Habib

Modeling and simulating coverage in sensor networks

The coverage problem in wireless sensor network is to place sensor devices in a service area so that the entire service area is covered. We have modeled the coverage problem as two sub-problems: floorplan and placement. The floorplan problem is to partition the service area into well-defined geometric cells, where the placement problem is to assign the sensor devices into a set of cells. Our proposed model has transformed the search space from a continuous into discrete, where the cardinality of the set of cells represents all possible candidate locations to place the sensors. Thus, we have reduced the complexity of the coverage problem, but we have had to merge the two sub-problems (floorplan and placement) into a single optimization problem to achieve good solutions. The objective function is to maximize the coverage of the service area while not exceeding a given budget. The merged optimization problem has been coded into an evolutionary approach and our results present an interesting finding between the cell size and sensors radius of coverage.

Comparative study between the internal behavior of GA and PSO through problem-specific distance functions

The evolutionary approach is a family of probabilistic search algorithms. The genetic algorithm (GA) and particle swarm optimization (PSO) are members of the evolutionary family, where both GA and PSO have been proven to be successful in finding good solutions in a short time for many combinatorial problems. In this paper, we have proposed several metrics, in the form of distance functions (DP), to examine and compare the internal behavior of GA and PSO based on a problem-specific DF rather than an algorithmic DF. Our initial experimental results show that PSO has more smooth and steady distance function values than GA.

Sensitivity Study of Sensors' Coverage within Wireless Sensor Networks

The coverage problem in wireless sensor networks is to place sensor devices in a service area so that the entire service area is covered/sensed. We have modeled the coverage problem as two sub-problems: floorplan and placement. The floorplan problem is to partition the service area into well-defined geometric cells, whereas the placement problem is to assign the sensor devices into a set of cells. The cardinality of the set of cells is considered as all possible candidate locations to place the sensors; therefore, we transformed the search space from continuous to discrete. Thus, we have reduced the complexity of the coverage problem, but we have merged the two sub-problems (floorplan and placement) into a single optimization problem to achieve good solutions. The objective function is to maximize the coverage of the service area while not exceeding a given budget. The merged optimization problem has been coded into the evolutionary approach. We have conducted five studies, where three studies compare the behavior of coverage ratio, cost, and radius of coverage of all allocated sensors with the number of generations separately. The fourth study examines the cell size versus coverage ratio. The fifth study looks at the average number of neighbors covered by a sensor with respect to the generations. Our experimental results present interesting findings in all five studies and our computerized evolutionary methodology generates solutions under 5 minutes.

Automated design of hierarchical intranets

This paper describes the use of i-CAD, a prototype tool for automatically synthesizing application specific intranets. i-CAD is a novel intranet computer-aided design software tool, and its ultimate goal is to concurrently design hierarchical network topologies and data management (content distribution) systems for data-intensive multimedia intranets. The prototype software tool introduced here synthesizes a three-level intranet architecture that entails minimal installation cost and yet enables all an intranets clients to perform their tasks with acceptable performance. The tool chooses network technologies (hardware resources and protocols) based on requirements specified by the user and determines the topology. An evolutionary approach is used to search the design space for a minimal cost three-level network. The experimental results for several network design problems described here indicate the effectiveness of the prototype network tool in finding good designs from a large design space in a reasonable amount of time.

Data aggregation at the gateways through sensors' tasks scheduling in wireless sensor networks

The authors present a novel graph-based model for aggregating sensors’ data at the gateways within wireless sensor networks (WSNs), where the proposed graph can act as a mean of guiding and assessing the needed resources for data aggregation. In this study, the authors have modelled all sensors’ tasks in a graph so that their collected data are to be smoothly aggregated (scheduled) at the gateway without losing or overlapping the collected data at the gateways. A typical WSN comprises of hundreds of sensors and few gateways; moreover, each sensor executes periodically and sequentially three tasks, which are sensing, processing and transmitting. The three tasks are modelled as a directed acyclic graph (DAG) per sensor, and then all DAGs are grouped into a super task-flow-graph (STFG). The data aggregation problem is solved by scheduling the tasks within STFG, where the authors have utilised three scheduling algorithms: as soon as possible, as late as possible and branch-and-bound. The simulation results for 50 sensors covering an area of 10 000 m2 utilising deterministic and stochastic execution models show a requirement of eight and six gateways, respectively, with minimal waiting time for aggregating the collected data from sensors to the gateways.

Supporting multimedia applications through network redesign

Recent evolutions in high-performance computing and high speed broadband Internet access have paved a way to enterprise-wide multimedia applications, which require stern QoS from the underlying networks. In this paper, we have explored threefold studies on existing enterprise network, whereby we proposed an analytical approach to evaluate the performance of the existing network; we have examined the feasibility of existing enterprise networks to accommodate voice over Internet protocol VoIP services with acceptable QoS, and we have redesigned the enterprise network to accommodate VoIP services to comply with the user defined QoS. The network performance is evaluated by number of VoIP calls sustained by the network, bandwidth utilization, loss rate and latency through Network Simulation NS-2 tool. We have derived a cost model to show the cost-effectiveness of VoIP services over telephonic network. For a medium-size enterprise network of 200 clients and 9 servers, our simulation results show that the redesign improves the network performance by increasing the number of VoIP calls by 57% and decreasing bandwidth utilization and packet loss rate by 20% and 7%, respectively. Moreover, the proposed network redesign demonstrates that the network can be scalable and it can handle up to 4% increased voice calls in the future maintaining QoS standards. Copyright

Self-organization in ambient networks through molecular assembly

An ambient network provides a homogeneous environment to the mobile node amidst the heterogeneity, which arises from the connections to various clusters over its lifespan. When a mobile node in an ambient network changes its location or communication pattern, these changes force the mobile node to join a new cluster. Therefore, we have extended the molecular self-assembly for the ambient network to search for the best set of clusters to seize all the nodes. An internal-view of a molecular system depicts all its molecules and their relationships as holding together due to the equilibrium between the attraction and repulsion forces among its molecules. Here we have analogized the nodes within the ambient network as molecules where these nodes are also governed by special-forces (relations) to configure a connected topology. In this paper, we have defined three forces, which are the physical distance, incoming traffic and outgoing traffic with respect to the pair-wise relations between the node-to-node (at micro-level of a cluster in an ambient network), to act as attraction and repulsion among nodes and forming clusters in a self-organized manner. The ambient network topology problem is formulated as an optimization problem to find suitable clusters of nodes with an objective to reduce the backbone traffic where a cluster assembles the strongly attracted nodes together with respect to all three forces. The simulation results show that our proposed molecular assembly (MA) algorithm embedded on each node coordinates the clustering and our algorithm leads in reducing the backbone traffic up to 20% under the influence of an individual force and up to 10% with the forces applied together when compared to our previous network redesign algorithm with genetic algorithm (GA), which offered reduction in backbone traffic up to 3% as an optimization tool. The robustness of the proposed algorithm is tested by varying the network sizes with 25 and 50 nodes and the convergence rate of MA, which is faster in comparison with GA.

Assessing and Redesigning Enterprise Networks through NS-2 to Support VoIP

Abstract In the recent past, Voice over IP (VoIP) deployments over data networks are gaining popularity due to the massive growth in the broadband internet access. Successful deployment of these applications depends directly on the performance of the underlying data network. Based on this and the fact that todays data networks are operated to perform many significant applications, network administrators seek out a way to measure the impact of these applications on the existing network performance before deploying them. O ccasionally, network redesign is necessity; considering redesigns alterations should preserve most of the existing network characteristics to reduce overall impact of deploying new applications in the network performance. In this paper, we evaluated readiness of the existing enterprise network through NS-2 to support VoIP and based on findings a solution for redesigning the enterprise network is proposed to enhance the new network performance and leaving sufficient capacity for future growth. We applied our approach on a medium size enterprise network as a case study, the results prove improvements in network performance after redesigning the existing enterprise network.

A coverage restoration scheme for wireless sensor networks within Simulated Annealing

This paper presents a simple but an effective approach to restore the coverage within a wireless sensor network (WSN) when sensors fail without adding new sensors. We have considered a sensor node failure due to electrical faults or malfunctions during the initial deployment. Each sensor has a limited energy supply, and the failure of a sensor results in extra overhead during restoration of the uncovered regions of the failed sensors on the active sensors. Therefore, we have proposed a restoration problem, which is to find the nearest and most apt neighbor in order to cover the uncovered region and at the same time maintain the lifespan of WSN to an accepted level. We have developed a restoration scheme within an optimization search algorithm, Simulated Annealing- a generic probabilistic metaheuristic algorithm. Our scheme searches the neighborhood space of the failing sensors in west-first counterclockwise. Our algorithm analyzes all the categories of failed nodes and the computational results show that our algorithm assists to increase the coverage area of the failing sensors with optimized energy consumption.

Exploring network topology evolution through evolutionary computations

We present an evolutionary methodology that explores the evolution of network topology when a uniform growth of the network traffic is considered. The network redesign problem is formulated as an optimization problem, subject to a set of design and performance constraints, while minimizing the redesign cost by maintaining as many as possible of the network devices that constitute the original topology. The experimental results for a 3-level network redesign problem (consisting of 65 client nodes) demonstrate the value of the search technique within the genetic algorithms in finding good solutions with respect to redesign cost and time.