Team dionysos

Overall Objectives
Scientific Foundations
Application Domains
New Results
Contracts and Grants with Industry
Other Grants and Activities

Section: New Results

Wireless networks

Participants : Bruno Sericola, Nizar Bouabdallah.

Efficient mobility management is one of the major challenges for next-generation mobile systems. Indeed, a mobile node (MN) within an access network may cause excessive signaling traffic and service disruption due to frequent handoffs. The two latter effects need to be minimized to support quality of service (QoS) requirements of emerging multimedia applications. In our work, we propose a new adaptive micro-mobility management scheme designed to track efficiently the mobility of nodes so as to minimize both handoff latency and total signaling cost while ensuring the MNÕs QoS requirements [19] . We introduce the concept of residing area. Accordingly, the micro-mobility domain is divided into virtual residing areas where the MN limits its signaling exchanges within this local region instead of communicating with the relatively far away root of the domain at each handoff occurrence. A key distinguishing feature of our solution is its adaptive nature since the virtual residing areas are constructed according to the current network state and the QoS constraints. To evaluate the efficiency of our proposal, we compared our scheme with existing solutions using both analytical and simulation approaches. Numerical and simulation results show that our proposed scheme can significantly reduce registration updates and link usage costs and provide low handoff latency and packet loss rate under various scenarios.

One of the major concerns in multi-hop wireless networks, called also wireless mesh networks (WMNs), is the radio resource utilization efficiency, which can be enhanced by managing efficiently the mobility of users as well as the interference effect among neighboring links. Our main objective is therefore to route efficiently the traffic generated by mobile nodes including the signaling messages in order to optimize network radio resource utilization. In other words, we aim at minimizing the total signaling cost by controlling the number of registration updates with the root of the domain. To achieve this, we propose new micro-mobility management schemes based on clustering techniques to track efficiently the mobility of nodes within the network. These mechanisms are conceived to minimize the total signaling cost of exchanged messages needed to manage the mobility of nodes as well as to optimize the link usage cost of the data traffic generated by each mobile user [18] .

Specifically, we proposed a new interference-aware routing metric as well as two mobility-aware clustering algorithms that take into consideration the mobility properties of users in order to improve the WMN performance. We prove that both clustering schemes can achieve significant gains in terms of radio resource utilization and load balancing, especially when using our interference-aware routing metric. Hence, and as a main contribution, we show that by taking into account the interference effect between links, we can improve the performance of our clustering algorithms and increase the gain initially observed with the conventional hop-count metric.

As a second alternative to increase the capacity of wireless mesh networks, we propose using the cognitive radio (CR) capabilities. The capacity of a WMN is indeed dependent on the spectrum resources it has, and the efficiency with which it uses them.

Most current WMNs rely on existing technologies such as IEEE 802.11, and operate using unlicensed spectrum. This has contributed to the rapid growth of the technology, as WMNs have been deployed across campuses, rural regions, and even entire cities. However, the bandwidth-intensive nature of WMNs - the result of using multi-hop communication in a shared medium - creates difficulties for delivering satisfactory quality-of-service (QoS), particularly for networks sharing spectrum with other networks and technologies

In our work, we considered the use of cognitive radio to improve this efficiency, by allowing networks belonging to different service providers to share both spectrum and infrastructure resources according to several different models. Using an ILP based problem formulation, this approach is demonstrated to yield significant benefits to the networks, by increasing QoS or allowing the networks to decrease their spectrum requirements.

In terms of virtual wireless networks (VWNs), despite having no dedicated spectrum resources, the feasibility of supporting QoS is demonstrated. These VWNs benefit from having multiple primary networks from which they can borrow resources. The VWN supports additional users, and considerably increases the utilization of channel resources. The successful operation of the VWN shows that the previously wasted spectrum resources of the primary networks have significant value.

Finally, in large scale multi-hop wireless networks, flat architectures are typically not scalable. Clustering was introduced to support self-organization and enable hierarchical routing. When dealing with multi-hop wireless networks, robustness is a crucial issue due to the dynamism of such networks. Several algorithms have been designed for clustering. In [22] , we show that a clustering algorithm that previously exhibited good robustness properties, is actually self-stabilizing. We propose several enhancements to the scheme to reduce the stabilization time and thus improve stability in a dynamic environment. The key technique to these enhancements is a localized self-stabilizing algorithm for Directed Acyclic Graph (DAG) construction. We provide extensive studies (both theoretical and experimental) that show that our approach enables efficient yet adaptive clustering in wireless multi-hop networks.


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