Monique Becker

Experimental Study: Link Quality and Deployment Issues in Wireless Sensor Networks

In this paper, we highlight the extent of the effects of topological specificities on the deployed solutions, which can be useful to refine already proposed models as well as to carry out protocol tuning or adjustments. We present, an intensive experimental study on wireless Link Quality Indicator (LQI). Using Moteivs Tmote Sky sensors, we deployed multiHopLQI algorithm of TinyOS in various network configurations: homogeneous and heterogeneous; straight-line and grid topologies with various transmission power levels and distances. Initially, we study LQI time-varying and try to understand the relationship between transmission power level, distance and link quality and present how some random disturbances due to external (physical changes) or internal phenomena (node movement,power variation) may affect the dynamics of the network. Later, we address impacts and side effects of position and power transmission level of some important nodes in the network like the Base Station in such LQI based algorithms.

Achieving Small-World Properties using Bio-Inspired Techniques in Wireless Networks

It is highly desirable and challenging for a wireless ad hoc network to have self-organization properties in order to achieve wide network characteristics. Studies have shown that Small-World properties, primarily low average path length (APL) 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 of distribution that lies between geometric and power law. In this paper, we show that in a wireless ad hoc network with non-uniform node density with only local information, we can significantly reduce the APL and retain the clustering coefficient. To achieve our goal, our algorithm first identifies logical regions using the Lateral Inhibition technique, then identifies the nodes that beamform and finally the beam properties using Flocking. We use Lateral Inhibition and Flocking because they enable us to use local state information as opposed to other techniques. We support our work with simulation results and analysis, which show that a reduction of up to 40% can be achieved for a high-density network. We also show the effect of hopcount used to create regions on APL, clustering coefficient and connectivity.

Using LQI to improve clusterhead locations in dense zigbee based wireless sensor networks

In WSN, it is not often desirable to use the GPS technology. Indeed, the use of GPS is expensive and may reduce the overall network performance. Moreover, indoor reception of the GPS signal is not possible. The Link Quality Indicator (LQI) is defined in the 802.15.4 standard, but its context of use is not specified in this standard. Some works on the LQI, few of which are field experiments, have shown that the LQI decreases as the distance increases. However, the challenge of clustering mechanisms is to form the smallest number of clusters by maximizing distances separating cluster heads to provide an efficient cover of the network and also minimizes the cluster overlaps. This reduces the amount of channel contention between clusters, and also improves the efficiency of algorithms that run at the level of the cluster heads. Therefore we propose an analytical model based on the use of the LQI in order to derive an optimally one-dominating set in which the smaller distance separating two cluster heads is improved.

Correction, generalisation and validation of the max-min d-cluster formation heuristic

The justification for using mutihop clusters may be found in [1]. In the well known heuristic proposed in [2], the d-dominating set of clusterheads is first selected by using nodes identifiers and then clusters are formed. In this paper we generalise this algorithm in order to select nodes depending of a given criterion (as the the degree, density or energy of nodes). The first section of this paper simplifies and proves the correctness of our generalised algorithm to select clusterheads. The cluster formation process proposed in [2] is extensively studied in the second section and is proved to be false.

Studying ENUM Performance with Modeling and Simulation

The new IETF protocol ENUM uses the DNS to bind existing phone numbers into set of informations (email address, SIP phone number etc.). Success of ENUM will depend on whether the DNS can achieve a performance similar to the database used in classical voice services. In order to study the DNS performance we designed a new way to measure and model a single DNS server behavior. We also modeled and measured the IP links connecting the DNS devices: resolver, cache server and authoritative servers. Finally we created a simulation model which enables us to simulate ENUM traffic. We then use the parameters obtained from the previous two models as input values into this simulator. The numerical results obtained from the simulation, was compared to real measurements in order to validate the global model. We plan to use the simulator to study different scenarios by varying different parameters. This will lead to recommendations of the new ENUM protocol to achieve the best performance

Dimensioning an ATM switch based on a three-stage Clos interconnection network

ATM (asynchronous transfer mode) is a new technique for transmitting voice, data and video. The performance of atm networks will depend on switch structure. Performance analysis of an atm switch based on a three-stage Clos network is presented. In this paper two types of switches are studied: a switch with input queues in the switching elements and a switch with output queues. This study is at the cell level and intends to dimension the switch. First, the traffic is supposed to be uniform, cells arrive on each input according to a geometric arrival process, they are uniformly directed over all the network outputs. An analytic model is proposed for both input and output queues in the switching elements. A study of the saturation throughput is proposed for input buffer switching elements. This work proves the influence of buffer dimensioning on the different stages of the switch. Dissymmetric switching elements are shown to be better than symmetric ones. A model is then designed for nonuniform traffic patterns and output buffers. Two types of non-uniform traffic are presented: single source to single destination (sssd) and multi-hot spots traffic (mhs). Discrete event simulations are used to validate the different models.RésuméĽatm est la nouvelle technique de transmission de la voix, des données et des images video. Les performances des réseaux atm dépendront de la structure des commutateurs. Les auteurs présentent le dimensionnement ľun commutateur qui est un réseau de Clos à 3 étages. Deux technologies différentes sont considérées, elles conduisent à des files ľattente en entrée ou en sortie. Ľétude est faite au niveau des cellules. On considère ľabord des trafics de Bernouilli de même loi sur toutes les entrées, avec équidistribution des destinations. Un modèle analytique est proposé dans les deux cas: files en entrée et files en sortie. Dans le cas des files en entrée, on étudie le débit maximal à saturation. Cette étude prouve ľinfluence de la répartition des tampons sur les différents étages. Il apparaît que des éléments de commutation dissymétriques sont meilleurs que des éléments symétriques. Un modèle est introduit pour la résolution du commutateur soumis à un trafic dissymétrique, pour le cas des files en sortie. Deux cas de trafics dissymétriques sont considérés: celui où une entrée envoie une forte charge vers une sortie et celui où il y a quelques entrées plus chargées destinant leur trafic à quelques sorties. Les différents modèles sont validés par simulation.

Cross layer simulation: application to performance modelling of networks composed of MANETs and satellites

The Cross layer concept is a new way to see the quality of service in the network. It consists in adapting the current mechanisms at one level to the underlying levels and the definition of information to share between, not necessarily adjacent, levels and the global optimisation instead of multiple optimisations. Performance optimisation of the whole system is a crucial step in the process of design and validation of new systems. Models of large, complex and dynamic systems can often be reduced to smaller sub-models, for easier analysis, by processes known as decomposition or aggregation methods. Those techniques have to be implemented in a dynamic simulation tool. It has to be dynamic because simulations are driven by dynamic data and entail the ability to incorporate additional data (either archived or collected online) and reversely the simulator will be able to dynamically steer the measurement process.

A distributed link quality based d-clustering protocol for dense ZigBee sensor networks

The Link Quality Indicator (LQI) is defined in the 802.15.4 standard, but its context of use is not specified in this standard. Some works on the LQI, few of which are field experiments, have shown that the LQI decreases as the distance increases. In WSN, it is not often desirable to use the GPS technology. Indeed, the use of GPS is expensive and may reduce the overall network performance. Moreover, indoor reception of the GPS signal is not possible. However, in cluster formation, it is quite important to sufficiently outspread the clusterheads (or caryommes) in order to improve the network efficiency. Therefore we propose a LQI based d-clustering protocol (LQI-DCP) which produces clusters of which each clusterhead has a better positioning regarding the locations of other clusterheads. Simulation results show that the caryommes resulting from LQI-DCP are sufficiently outspread. LQI-DCP also reduces the density of clusterheads and then improves the WSN energy efficiency, while each sensor remains still at less than d-hops from a caryomme.

Virtual base station election for wireless sensor networks

In a classical wireless sensor network, a base station is often present to ensure efficient data collection. Endowed with typical hardware feature, especially with high energy level and good stockpiling capabilities, the base station completes the architecture as a required component for a wide range of applications. However, there are some projects where base station deployment should be avoided without reducing network efficiency. Thus, in a cold chain supervision project, itŠs not necessary to add base station to a wireless sensors network deployed inside a food or a medical truck. In this manner, it is a low-budget sensors network deployment. Moreover, such applications have to replicate data across all nodes and to maintain same information as well. In this paper, we propose databases updating model for homogeneous wireless sensors network deployed in a food truck without any base station. In this model, Virtual Base Station (VBS) is the node which is elected to act as classical base station during a specific period of time. Virtual Base Station (VBS) electionŠs algorithm is based on the remaining energy for each node and latest Virtual Bases Station (VBS) to reduce overall energy spent by network. Simulation results (using MATLAB) show that VBS model introduces very low overhead with respect to the classical network with permanent Base Station (BS).

ATCR: an adaptive time-based channel reservation mechanism for LEO satellite fixed cell systems

In this paper, we propose an adaptive time-based channel reservation mechanism (ATCR) suitable for handover and call admission procedure control in future multiservices mobile satellite systems. These systems are characterized by a high rate of handover. While guaranteeing a null handover failure probability, by using a channel reservation strategy in the cells to be crossed by the user, ATCR optimizes the utilization of resources. The performance of our mechanism has been compared to other schemes. ATCR method has the advantage of a better channel utilization by sharing channels between users. An approximate analytical model has been developed, and its results have been validated through simulations.