Réseau de capteurs sans fil : étude en vue de la réalisation d'un récepteur GPS différentiel à faible coût

A Wireless Sensor Network (WSN) consists of a set of wireless nodes where their number can be very large. The WSN is used to perform a specific task for an application. The WSN has become increasingly popular due to their wide range of civil and military applications: smart planet, smart home, smart care, M2M (Machine to Machine)... The ultimate goal of a WSN is to monitor an area of interest, but to achieve that, several objectives (services) must be implemented. These services include: synchronization between nodes, localization, topology management, data aggregation, data storage, etc. The node's localization is one of the most important services. It associates to each node the coordinates of its position. Several methods are used to achieve this function. A set of systems (technologies) have been developed to provide this service. The most commonly used outdoors, worldwide, by far is the GPS (Global Positioning System). It has the advantage of providing the position (and time) continuously and in all weather conditions. However, the accuracy of GPS does not meet the requirements of all applications, thus it is necessary to improve GPS accuracy. For this, the differential mode (DGPS, Differential GPS) is introduced. It uses a base station that monitors the GPS errors, calculates corrections and transmits them through a wireless access medium; but the installation of a differential station (RTK, Real-Time Kinematic) is difficult and very expensive. The differential mode inspires this thesis, but in contrast to the RTK solution that uses a large base station, the original solution proposed in this thesis (LCD-GPS, Low Cost Differential GPS, Local Cooperative DGPS) is based on using a WSN equipped with low cost standard GPS receivers. Works conducted to improve the GPS accuracy include the use of a digital map (Map Matching), the simple difference, the intelligent difference, the filtering and a global correction. To evaluate this solution, a hardware and software platform has been developed; it consists of a network of wireless nodes called LiveNodes (LIMOS Versatile Embedded Node). The software part is composed particularly of an embedded operating system called LIMOS (Lightweight Multi-Threaded Operating System) and a wireless communication protocol called CIVIC (Inter Vehicle Communication and Intelligent Cooperative) and finally the specific processing of LCD-GPS solution. The results show that the LCD-GPS can be used for various applications but it is very sensitive to the environment (multipath). However, it is noted that the WSN can generally achieve a robust and reliable location sensor.Les travaux menés dans cette thèse visent à améliorer la précision du GPS en s'inspirant du mode différentiel (DGPS, Differential GPS). Mais à l'inverse de la solution RTK (RTK, Real-Time Kinematic) qui utilise une grande station de base et qui est difficile à installer et surtout très onéreuse, la solution originale proposée dans cette thèse (LCD-GPS, Low Cost Differential GPS, Local Cooperative DGPS) est basée sur l'utilisation d'un Réseau de Capteurs Sans Fil (RCSF) équipés de récepteurs standarts à faible coût. Ces travaux incluent l'utilisation d'une carte numérique (Map matching), la différence simple, la différence intelligente le filtrage la correction globale ...Afin d'évaluer cette solution, une plateforme matérielle et logiciel a été développée, elle consiste en un réseau de capteurs appelés LiveNodes (LIMOS Versatile Embedded Node). La partie logicielle est composée notamment d'un système d'exploitation embarqué appelé LIMOS (Lighweight Multi-thtreading Operating System) et d'un protocole de communication sans fil appelé CIVIC (Communication Inter Vehicule Intelligente et Coopérative) et enfin les traitements propres à la solution LCD-GP