Description
Date depot: 1 janvier 1900
Titre: Small World Networks in Motion
Encadrant :
Vincent GAUTHIER (SAMOVAR)
Directrice de thèse:
Monique BECKER (LTCI (EDMH))
Domaine scientifique: Sciences et technologies de l'information et de la communication
Thématique CNRS : Non defini
Resumé:
{{{Introduction}}}
The aim of this thesis is to provide a model for dynamic networks. Many networks are dynamic and their topology changes rapidly—on the same time scale as the communications of interest between network nodes. Examples are the human contact networks involved in the transmission of disease, ad hoc radio networks between moving vehicles, and the transactions between principals in a market. While we have good models of static networks, so far these have been lacking for the dynamic case. A better understanding of the dynamic of networks should enable us to design and engineering networks toward reliable and self-organized network infrastructure that dynamically adapts to the change in the network (the users mobility for example). It is highly desirable and challenging for a wireless ad hoc network for example to have self-organization properties in order to achieve network wide characteristics.
With good model of the networks dynamic (an example can be show in our previous studies in [3]) we can extract from the model information about nodes of structural importance for the networks, and further on reengineering the networks toward a adapted topologies design that have more desirable desirables properties.
{{{Research Objectives}}}
Our previous studies [1,2] have shown that Small World properties, primarily low average path length and high clustering coefficient, are desired properties for networks in general. However, due to the spatial nature of the wireless networks, achieving small world properties remains highly challenging. Studies also show that wireless ad hoc networks with small world properties show a degree distribution that lies between geometric and power law. We also have shown that in a wireless ad hoc network with non-uniform node density using only local information, we can significantly reduce the average path length and retain the clustering coefficient.
In a wireless ad-hoc network, achieving small world properties can help us in many ways. Having a low Average Path Length (APL) would increase the performance of the network in terms of communication [4], [5] (reduced traffic per unit area, reduced congestion and reduced signal interference), low latency and reduce the overall energy consumption in the network during the data communication. On the other hand, maintaining the Clustering Coefficient (CC) would ensure connectivity to the neighbourhood and would make the network resilient [6], [7]. However, Watts’ model cannot be applied directly to spatial networks because of the spatial nature of such networks. In spatial networks, addition of a shortcut between any two nodes should depend on the distance between two nodes. Helmy in [8] first studied the effect of adding few distance-limited links in the network. He showed that, upon introduction of distance-limited links, wireless ad hoc networks show small world properties. He concluded that, when the shortcut lengths are 1/4th of the network diameter, there is a maximum reduction in the APL. Thus, proving that realization of small world properties in a wireless ad-hoc network depends crucially on the length of shortcuts created among nodes. Another important factor in the realization of small world properties is the choice of nodes among which shortcuts are to be created. One method to obtain these nodes is that of preferential attachment [9], [12], typically observed in real world networks, wherein links are created to nodes with high structural importance. It was shown that, analogous to real world networks, using preferential attachment for creation of distance- limited links in a spatial network resulted in reduced network diameter [10], [11]. This was accompanied by high clustering coefficient and a shift in the node degree distribution towards scale free. These results motivate us to say that, creation of links to nodes having high structural importance in the network can result in the desired small world characteristics.
Having already explore what are some of desirables topological properties of spatial graph, the main research objective of this thesis is now to provide a engineering design to model the network dynamic and use this information to enable the networks structure adapt in Self-organized fashion. A Network model that adapts itself to the structural change imposed by the mobility for example could potentially lead various applications even outside the networking realm.
---
{{{References}}}
-# R. Agarwal, A. Banerjee, V. Gauthier, M. Becker, C. K. Yeo, and B. S. Lee, “Achieving Small World Properties using Bio-Inspired Techniques in Wireless Networks,” (To appear) Special Issue on Security and Performance of Networks and Clouds (The Computer Journal), Sep. 2012.
-# A. Banerjee, R. Agarwal, V. Gauthier, C. K. Yeo, H. Afifi, and B. S. Lee, “A Self-Organization Framework for Wireless Ad Hoc Networks as Small Worlds,” (To appear) in IEEE Transaction on Vehicular Communica
Doctorant.e: Asgari Fereshteh