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

Section: New Results

Autonomous wireless networking


The capacity of a network is a fundamental characteristic of a network which depends on many criteria. [6] proposes a complete framework to compute the upper and the lower bounds of the network capacity according to a physical topology and a given routing protocol. The radio resource sharing principles of CSMA-CA is modeled as a set of linear constraints with two models of fairness. The first one assumes that nodes have a fair access to the channel, while the second one assumes that on the radio links. We then develop a pessimistic and an optimistic scenarios for radio resource sharing, yielding a lower bound and an upper bound on the network capacity for each fairness case. Our approach is independent of the network topology and the routing protocols, and provides therefore a relevant framework for their comparison. We apply our models to a comparative analysis of a well-known flat routing protocol OLSR against two main self-organized structure approaches, VSR and localized CDS.

self-organization in WSN:

The goal of the self-organization is to structure the wireless sensor networks (WSN) using a connected logical topology (backbone) or a non connected one (clusters) in order to introduce stability and robustness. More, networking protocols based on such virtual structures should lead to better performances than the classical flat approach. Two models of self-organization have been studied by SWING: virtual coordinates [10] , [9] , [36] , [35] and graph-based organization [24] .

[10] , [9] , [36] , [35] introduce and analyze the concept of virtual coordinates. These coordinates are chosen randomly when a node is switched on, and are updated each time the node relays a packet. As this process goes on, the virtual coordinates of the nodes converge to a near-optimal state. When using a greedy geographic approach on top of these coordinates, we show that the number of hops to reach the destination exceeds the shortest path by a few percent only. Moreover, our approach guarantees delivery even when nodes appear/disappear in the network, and under realistic transmission models. We analytically prove the correctness of our protocol. Moreover, extensive simulations are used to show that our position-free solution outperforms existing geo- graphic protocols - such as Greedy-Face-Greedy (GFG) or Greedy Perimeter State- less Routing (GPSR) - in terms of energy-efficiency, path length and robustness. [37] proposes three new simple and effective strategies for constructing virtual coordinate in wireless sensor networks with unreliable links. We simulate the greedy routing protocol which uses the virtual coordinate constructed by our proposed strategies under unreliable links. Simulation results show that the delivery ratio of our proposed strategies is higher than the delivery ratio of the existing one, and closer to the delivery ratio of the real coordinate under unreliable links, without introducing any additional cost.

During the thesis of Karel Heurtefeux [1] , the qualitative location algorithm for topology control (QLoP) has been proposed and studied. QLoP computes a Relative Neighborhood Graph to define an efficient routing algorithm. Therefore, QLoP can classify its own neighborhood according to its logical distance. In [24] , we show that QLoP offers a better delivery rate and a better average distance than solution based on flat routing.

Real-time and other works:

Duty-cycle prolongs the lifetime of battery-powered wireless sensor networks (WSNs). However, it incurs additional delay because the nodes may be asleep. In addition to energy constraints, many applications have real-time constraints, which means the sink has to be informed before a deadline when an event occurs. Moreover, wireless links among low power radios are highly unreliable. These pose big challenges to design protocols for real-time applications. In [13] , a novel forwarding scheme based on distributed wakeup scheduling is proposed which can guarantee bounded delay and have higher delivery ratio for ultra low duty-cycle WSNs under unreliable links. The proposed wakeup scheduling algorithm schedules the wakeup time of each node according to the hop number and expected delivery ratio to the sink. We model the forwarding scheme and analyze its properties. Simulation results show that the proposed algorithm has better performances in terms of delivery ratio and end-to-end delay.

[55] analyzed the Prophet dynamic address allocation protocol described at INFOCOM 2003. This protocol is based upon a family of pseudo-random generators. The goal of Prophet is to establish an addresses scheme free of conflict. The addressing capabilities of Prophet depend on the underlying properties of the pseudo-random generators. The different pseudo-random generators proposed in Prophet are analyzed and the limits of the scheme are exhibited. Most notably, the periods of the generators limit the addressing capabilities of a node and the fact that Prophet is collision-free. In this research report, we show that the underlying assumptions made in Prophet can not be met by pseudo-random generators.


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