3,680 research outputs found
Proposition and validation of an original MAC layer with simultaneous medium accesses for low latency wireless control/command applications
Control/command processes require a transmission system with some
characteristics like high reliability, low latency and strong guarantees on
messages delivery. Concerning wire networks, field buses technologies like FIP
offer this kind of service (periodic tasks, real time constraints...).
Unfortunately, few wireless technologies can propose a communication system
which respects such constraints. Indeed, wireless transmissions must deal with
medium characteristics which make impossible the direct translation of
mechanisms used with wire networks. The purpose of this paper is to present an
original Medium Access Control (MAC) layer for a real time Low Power-Wireless
Personal Area Network (LP-WPAN). The proposed MAC-layer has been validated by
several complementary methods; in this paper, we focus on the specific
Simultaneous Guaranteed Time Slot (SGTS) part
An IEEE 802.15.4 based adaptive communication protocol in wireless sensor network : application to monitoring the elderly at home
International audienceMonitoring behaviour of the elderly and the disabled living alone has become a major public health problem in our modern societies. Among the various scientific aspects involved in the home monitoring field, we are interested in the study and the proposal of a solution allowing distributed sensor nodes to communicate with each other in an optimal way adapted to the specific application constraints. More precisely, we want to build a wireless network that consists of several short range sensor nodes exchanging data between them according to a communication protocol at MAC (Medium Access Control) level. This protocol must be able to optimize energy consumption, transmission time and loss of information. To achieve this objective, we have analyzed the advantages and the limitations of WSN (Wireless Sensor Network) technologies and communication protocols currently used in relation to the requirements of our application. Then we proposed a deterministic, adaptive and energy saving medium access method based on the IEEE 802.15.4 physical layer and a mesh topology. It ensures the message delivery time with strongly limited collision risk due to the spatial reuse of medium in the two-hop neighbourhood. This proposal was characterized by modelling and simulation using OPNET network simulator. Finally we implemented the proposed mechanisms on hardware devices and deployed a sensors network in real situation to verify the accuracy of the model and evaluate the proposal according to different test configurations
MĂ©trologie pour l'analyse comparative des performances temporelles des liens Bluetooth
Cet article présente une étude métrologique des performances temporelles de la technologie de réseau sans fil Bluetooth. Cette étude est réalisée en collaboration avec le Centre Commun de Recherche d'EADS dans le but de connaßtre précisément le temps d'acheminement d'une donnée quelconque par le réseau Bluetooth. Les caractéristiques essentielles de Bluetooth ayant une forte incidence sur les performances temporelles sont présentées dans une premiÚre partie. Dans un second temps, l'étude métrologique est détaillée, du mode opératoire à la présentation des résultats. L'analyse de ces derniers montre que cette technologie présente des performances intéressantes sur le plan temporel, notamment dans son mode de transmission synchrone
Proposition of a full deterministic medium access method for wireless network in a robotic application
International audienceToday, many network applications require shorter react time. Robotic field is an excellent example of these needs: robot react time has a direct effect on its task's complexity. Here, we propose a full deterministic medium access method for a wireless robotic application. This contribution is based on some low-power wireless personal area networks, like ZigBee standard. Indeed, ZigBee has identified limits with Quality of Service due to non-determinist medium access and probable collisions during medium reservation requests. In this paper, two major improvements are proposed: an efficient polling of the star nodes and a temporal deterministic distribution of peer-to-peer messages. This new MAC protocol with no collision offers some QoS faculties
Conception d'une plateforme pluridisciplinaire ouverte et Ă©volutive pour l'Ă©valuation des technologies d'aide au maintien Ă domicile
National audienceLe papier prĂ©sente la rĂ©alisation dâune plateforme expĂ©rimentale innovante permettant dâoffrir un environnement dâĂ©valuation des technologies pour lâaide au maintien Ă domicile de personnes fragiles (personnes ĂągĂ©es, handicapĂ©es ou souffrant de maladies chroniques). Elle se concrĂ©tise sous la forme dâun appartement intelligent instrumentĂ© et de matĂ©riels interconnectĂ©s au travers dâune infrastructure de communication basĂ©e sur le standard KNX. Cette plateforme dâexpĂ©rimentation est le fruit dâun partenariat Ă©troit entre les acteurs de la recherche, de la formation et des acteurs Ă©conomiques. Ce projet est pluridisciplinaire puisquâil associe Ă la fois la dimension technique et la dimension psychosociologique au service de lâusager
Prototyping and Performance Analysis of a QoS MAC Layer for Industrial Wireless Network
Today's industrial sensor networks require strong reliability and guarantees
on messages delivery. These needs are even more important in real time
applications like control/command, such as robotic wireless communications
where strong temporal constraints are critical. For these reasons, classical
random-based Medium Access Control (MAC) protocols present a non-null frame
collision probability. In this paper we present an original full deterministic
MAC-layer for industrial wireless network and its performance evaluation thanks
to the development of a material prototype.Comment: 7th IFAC International Conference on. Fieldbuses and nETworks in
industrial and embedded systems, Toulouse : France (2007
The Sea Peoples, from cuneiform tablets to carbon dating
The 13(th) century BC witnessed the zenith of the Aegean and Eastern Mediterranean civilizations which declined at the end of the Bronze Age, similar to 3200 years ago. Weakening of this ancient flourishing Mediterranean world shifted the political and economic centres of gravity away from the Levant towards Classical Greece and Rome, and led, in the long term, to the emergence of the modern western civilizations. Textual evidence from cuneiform tablets and Egyptian reliefs from the New Kingdom relate that seafaring tribes, the Sea Peoples, were the final catalyst that put the fall of cities and states in motion. However, the lack of a stratified radiocarbon-based archaeology for the Sea People event has led to a floating historical chronology derived from a variety of sources spanning dispersed areas. Here, we report a stratified radiocarbon-based archaeology with anchor points in ancient epigraphic-literary sources, Hittite-Levantine-Egyptian kings and astronomical observations to precisely date the Sea People event. By confronting historical and science-based archaeology, we establish an absolute age range of 1192-1190 BC for terminal destructions and cultural collapse in the northern Levant. This radiocarbon-based archaeology has far-reaching implications for the wider Mediterranean, where an elaborate network of international relations and commercial activities are intertwined with the history of civilizations
Modelling the rotational curves of spiral galaxies with a scalar field
In a previous work (Mbelek 2001), we modelled the rotation curves (RC) of
spiral galaxies by including in the equation of motion of the stars the
dynamical terms from an external real self-interacting scalar field, ,
minimally coupled to gravity and which respects the equivalence principle in
the weak fields and low velocity approximation. This model appeared to have
three free parameters : the turnover radius, , the maximum tangential
velocity, , plus a strictly positive
integer, . Here, we propose a new improved version where the coupling of the
-field to dark matter is emphasized at the expense of its
self-interaction. This reformulation presents the very advantageous possibility
that the same potential is used for all galaxies. Using at the same time a
quasi-isothermal dark matter density and the scalar field helps to better fit
the RC of spiral galaxies. In addition, new correlations are established.Comment: Latex, 5 pages with 3 Postscript figure
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