Sonja Filiposka

Ad hoc networks connection availability modeling

One of the most important issues for mobile ad hoc networks is to know the availability of the system. In this paper we propose a generalized connection availability model based on real measurable parameters that concern the performances of mobile ad hoc networks. Detailed validation of the connection availability model is presented through simulations. The proposed model can be used for analysis or design of an ad hoc network that needs to satisfy a given connection availability level.

Cooperative method for wireless sensor network localization

In order to obtain an efficient wireless sensor network localization, several enhancements based on the decentralized approach are proposed. These features can be used in the cases when multiple distance measurements are used as input, where each node iteratively updates its estimated position using a maximum likelihood estimation method based on the previously estimated positions of its neighbors. Three novel features are introduced. First, a backbone is constructed, that is, a subset of nodes that are intermediaries between multiple beacon nodes, which guides the localization process of the other (non-backbone) nodes. Second, the space is perturbed more often during the earlier time steps to avoid reaching poor local minima in some cases regarding the localization optimization function. Third, for better localization of the non-backbone (or peripheral) nodes and avoidance of the rigidity problem, 2-hop neighboring distances are approximated. The introduced features are incorporated in a range-based algorithm that is fully distributed, shows good performance, and is scalable to arbitrary network size.

Grid Computing Implementation in Ad Hoc Networks

The development of ubiquitous computing and mobility opens challenges for implementation of grid computing in ad hoc network environments. In this paper, a new grid computing implementation for ad hoc networks is proposed. The proposed addition of the ad hoc network protocols suite offers an easy and effective way to exploit the computing power of the network nodes. The model is implemented in the NS-2 network simulator providing the possibility to investigate its performances and tune the network grid parameters.

Terrain-aware three-dimensional radio-propagation model extension for NS-2

One of the weakest points of modeling wireless systems is radio-signal propagation in an irregular space. For that reason, it is essential that, when analyzing the performances of wireless networks, we observe the network in a natural three-dimensional terrain and we use an appropriate propagation model. However, care must be taken since such simulations demand extensive processing power, especially for mobile scenarios. In this paper, we present an extension for the NS-2 simulator with our optimized Durkin’s propagation model based on digital elevation model data. Going one step further in creating a set of realistic simulation environments, we present a case study for modeling the behavior of a wireless ad hoc network via the social network of users grouped into scale-free communities. The case study presents a blend of topography responsive simulations with realistic traffic and movement pattern, while showing the numerous simulation possibilities of the presented extension.

Analysis of small world phenomena and group mobility in ad hoc networks

The main application of wireless mobile ad hoc networks is to offer services for situations wherein groups of people come together and share information. The groups of people that use the ad hoc network form some kind of social network. In this paper an analysis of the performances of mobile ad hoc networks is performed when taking into consideration its social characteristics through the small world phenomena of the application layer and usage of group-based mobility. The simulations show that the social interconnection between the network users has an extreme influence on the network performances. The results bring forth a different view on the real life deployment of ad hoc networks when compared to the poor performances of the purely randomized scenarios.

Durkin’s Propagation Model Based on Triangular Irregular Network Terrain

Propagation models that are commonly used in assessing the performances of ad hoc networks, take into account the mechanisms of reflection, diffraction and scattering on the ground. However, it must not be forgotten that the communication between devices is usually carried out in irregular terrain, so it’s necessary to use the terrain profile in order to determine the signal coverage. In this paper we layout the extension of the Durkin’s propagation model using Triangular Irregular Network (TIN) based terrain. The verification of the proposed propagation model is done by comparing the results with the ones obtained with a SRTM map used in the Radio Mobile software.

Balancing Performances in Online VM Placement

Optimal usage of data center resources has become one of the most important topics in the cloud computing research community. Increased efficiency alongside decreased power consumption becomes a desired goal. Crucial point in achieving this goal is the process of virtual machine placement. In this paper, we analyze and compare several heuristics aiming to evaluate their capabilities with special attention to balanced resource usage versus total number of used physical machines. The presented results identify the preferred placement heuristic that achieve maximum balancing performances based on the data center characteristics, size of the cloud services and their diversity.

Performances of clustered ad hoc networks on 3D terrains

Propagation prediction algorithms which use terrain information are typically used for the design of modern wireless systems. Therefore, it is essential that when analyzing the performances of ad hoc networks we observe the network in a natural 3D terrain and we use an appropriate propagation model. In this paper we explain our extension of the NS-2 simulator using Digital Elevation Model data and terrain aware propagation model. Because of the natural emergence of clustering in the network of users, we also study the relationship between the clustering in the ad hoc networks and different terrain profiles. The simulations show that, when the network clusters are accompanied with related terrain contours, the observed network performances demonstrate measurable enhancement.

Community-based VM placement framework

The ongoing trends in cloud computing demonstrate increasing need for efficient, yet economical data centers. Thus, recently the research community has focused its efforts on frameworks for optimised usage of the available resources that will result with energy-efficient and highly effective data centers. Toward this goal, in this paper we present a community-based framework for virtual machine placement inside a cloud data center. The framework is based on the complex network structural property of grouping tightly coupled nodes, and a matching process that maps virtual to physical communities while employing different optimisation functions on different hierarchy levels. The presented simulation results of the framework application reflect its high usage potential achieved by improvement in communication efficiency and reduced power consumption compared to the traditional heuristics.

Game Theoretic Approach for Discovering Vulnerable Links in Complex Networks

Complex networks have been an up-and-coming exciting field in the realm of interactions. With their widespread use appearing on the horizon it is ever more vital to be able to measure their vulnerability as a function of their topology. Precisely, discovering vulnerable links, disposed to attacks, can help in hardening these links and by that providing more secure and reliable network structure. This paper addresses the link vulnerability of different topologies of complex networks such as: random networks, geographic random networks, small world networks and scale-free networks. We introduce measure for vulnerability of complex networks, and prove by simulations that network vulnerability heavily depends on the network topology.