Some recent results of the CODALEMA experiment

Codalema is one of the experiments devoted to the detection of ultra high energy cosmic rays by the radio method. The main objective is to study the features of the radio signal induced by the development in the atmosphere of extensive air showers (EAS) generated by cosmic rays in the energy range of 10 PeV-1 EeV . After a brief presentation of the detector features, the main results obtained are reported (emission mechanism, lateral distribution of the electric field, energy calibration, etc.). The first studies of the radio wave front curvature are discussed as new preliminary results.Comment: Proc. of the annual meeting of the French Society of Astronomy & Astrophysics SF2A, Paris, June 2011, G. Alecian, K. Belkacem, R. Samadi and D. Valls-Gabaud (eds

A Dynamic Multimedia User-Weight Classification Scheme for IEEE_802.11 WLANs

In this paper we expose a dynamic traffic-classification scheme to support multimedia applications such as voice and broadband video transmissions over IEEE 802.11 Wireless Local Area Networks (WLANs). Obviously, over a Wi-Fi link and to better serve these applications - which normally have strict bounded transmission delay or minimum link rate requirement - a service differentiation technique can be applied to the media traffic transmitted by the same mobile node using the well-known 802.11e Enhanced Distributed Channel Access (EDCA) protocol. However, the given EDCA mode does not offer user differentiation, which can be viewed as a deficiency in multi-access wireless networks. Accordingly, we propose a new inter-node priority access scheme for IEEE 802.11e networks which is compatible with the EDCA scheme. The proposed scheme joins a dynamic user-weight to each mobile station depending on its outgoing data, and therefore deploys inter-node priority for the channel access to complement the existing EDCA inter-frame priority. This provides efficient quality of service control across multiple users within the same coverage area of an access point. We provide performance evaluations to compare the proposed access model with the basic EDCA 802.11 MAC protocol mode to elucidate the quality improvement achieved for multimedia communication over 802.11 WLANs.Comment: 15 pages, 8 figures, 3 tables, International Journal of Computer Networks & Communications (IJCNC

An Adaptive Multimedia-Oriented Handoff Scheme for IEEE 802.11 WLANs

Previous studies have shown that the actual handoff schemes employed in the IEEE 802.11 Wireless LANs (WLANs) do not meet the strict delay constraints placed by many multimedia applications like Voice over IP. Both the active and the passive supported scan modes in the standard handoff procedure have important delay that affects the Quality of Service (QoS) required by the real-time communications over 802.11 networks. In addition, the problem is further compounded by the fact that limited coverage areas of Access Points (APs) occupied in 802.11 infrastructure WLANs create frequent handoffs. We propose a new optimized and fast handoff scheme that decrease both handoff latency and occurrence by performing a seamless prevent scan process and an effective next-AP selection. Through simulations and performance evaluation, we show the effectiveness of the new adaptive handoff that reduces the process latency and adds new context-based parameters. The Results illustrate a QoS delay-respect required by applications and an optimized AP-choice that eliminates handoff events that are not beneficial.Comment: 20 pages, 14 figures, 4 table

Étude de l'énergie et du point d'émission radio des rayons cosmiques détectés dans l'expérience CODALEMA

The purpose of the CODALEMA experiment, installed at the Nançay Radio Observatory (France), is to study the radio-detection of ultra-high-energy cosmic rays. Distributed over an area of 0,25 km2, the original device uses in coincidence an array of particle detectors and an array of short antennas. A new analysis of the energy reconstruction from radio data obtained with this device is presented. We suggest that an energy resolution of less than 20% can be achieved and that, not only the Lorentz force, but also another contribution proportional to all charged particles generated during the shower development, could play a significant role in the amplitude of the electric field measured by the antennas (as an effect of coherence or of charge excess). Since 2011, a new array of radio-detectors, consisting of 60 stand-alone and self-triggered stations, has been in deployment over an area of 1.5 km2 around the first device. This new development leads to specific challenges which are discussed in terms of recognition of cosmic rays and reconstruction of the curvature of radio wave fronts. For commonly-used minimization algorithms, we emphasize the importance of the convergence process induced by the minimization ofa non-linear least squares function that affects the results in terms of degeneration of the solutions. We derive a simple method to obtain a satisfactory estimate of the location of the apparent emission source, which mitigates the problems previously.Le but de l’expérience CODALEMA, installée à l’observatoire de radioastronomie de Nançay (France), est d’étudier la radiodétection des rayons cosmiques d’ultrahaute énergie. Le dispositif initial, réparti sur une aire de 0, 25 km2, utilise en coïncidence un réseau des détecteurs de particules et un réseau d’antennes. Utilisant cet appareillage, une nouvelle analyse visant à estimer l’énergie de la gerbe à partir des données radio est présentée. Nous déduisons qu’une résolution en énergie meilleure que 20% peut être atteinte et que, non seulement la force de Lorentz, mais aussi une contribution proportionnelle à la charge totale produite dans la gerbe atmosphérique joue un rôle significatif dans l’amplitude du champ électrique mesuré par les antennes (effet de cohérence ou d’excès de charge). Depuis 2011, un nouveau réseau de détection radio, constitué de 60 stations autonome auto-déclenchées est en déploiement sur une superficie de 1, 5 km2 autour du dispositif initial. Ce développement conduit à des défis spécifiques en termes d’identification des gerbes atmosphériques et de reconstruction de la courbure des fronts d’onde radio. Concernant la localisation de la source apparente de l’émission radio, pour les algorithmes de minimisation courants, nous soulignons l’importance du processus de convergence induit par la minimisation d’une fonction non linéaire des moindres carrés qui peut induire une dégénérescence des solutions. Une méthode alternative d’estimation est proposée