Data Dissemination in Mobile Phone Sensor Networks

Deploying sensors over large areas is costly in terms of configuration, hardware, and maintenance. Using onboard sensors of today mobile phones can significantly reduce the expenses in monitoring areas and disseminating events or data. Via the available short-range Bluetooth and/or WiFi interfaces, measured data are not only gradually delivered, but also possibly more reliable. In our simulation, existing Delay-Tolerant Network routing algorithms show poor performance on a complex network comprising diverse kinds of sensor nodes, such as, mobile phones, cars, and road side units. New approaches that can perform well on such heterogeneous networks are needed. They also need to support exchanging measurements among sensors for more accurate inference. In the early phase, we set up a heterogeneous architecture composed of different sorts of sensors, and propose an algorithm, Unified routing, for routing and disseminating. A further variant of the scheme is being developed. Early simulation results are consistent with theoretical prediction. After finishing the firs step, Unified routing, the focus of our research will be on distributed data processing. Finally, routing and distributed data processing will be investigated in a testbed in a realistic context

Towards Opportunistic Data Dissemination in Mobile Phone Sensor Networks

Recently, there has been a growing interest within the research community in developing opportunistic routing protocols. Many schemes have been proposed; however, they differ greatly in assumptions and in type of network for which they are evaluated. As a result, researchers have an ambiguous understanding of how these schemes compare against each other in their specific applications. To investigate the performance of existing opportunistic routing algorithms in realistic scenarios, we propose a heterogeneous architecture including fixed infrastructure, mobile infrastructure, and mobile nodes. The proposed architecture focuses on how to utilize the available, low cost short-range radios of mobile phones for data gathering and dissemination. We also propose a new realistic mobility model and metrics. Existing opportunistic routing protocols are simulated and evaluated with the proposed heterogeneous architecture, mobility models, and transmission interfaces. Results show that some protocols suffer long time-to-live (TTL), while others suffer short TTL. We show that heterogeneous sensor network architectures need heterogeneous routing algorithms, such as a combination of Epidemic and Spray and Wait

Etude de l’influence des hétérogénéités microstructurales sur la tenue en fatigue à grand nombre de cycles des alliages d’aluminium de fonderie

This work treats the influence of the microstructural heterogeneities on the multiaxial high cycle fatigue (HCF) strength of cast aluminium alloys used in an automobile context. The characteristic microstructural heterogeneities present in this family of materials are the aluminium matrix (often characterised by the SDAS and/or the DAS and the precipitation hardening level), inclusions (silicon particles and intermetallics) and casting defects (oxide films and casting porosity).In order to clearly decouple these effects, three cast Al-Si alloys, obtained thank to different casting processes (gravity die casting and lost foam die casting) and associated with several heat treatments (T7 and Hot isostatic pressing-HIP), have been investigated. The HIP treatment is used in order to obtain a porosity free alloy. A vast experimental HCF campaign, including four loading modes (uniaxial (R=-1), torsion (R=-1), combined tension-torsion (R=-1) and equibiaxial tension (R=0.1)) has been undertaken. The following effects on the HCF behaviour have been characterised for the porosity free alloy as well as porosity containing alloys: (a) the effect of the multiaxiality (for the loading modes at R=-1), (b) the effect of the mean stress and (c) the effect of the biaxality (for equibiaxial tensile loads at R=0.1). The fatigue damage mechanisms have been studied in order to highlight the roles of the casting pores, the aluminium matrix and the inclusions on the fatigue damage mechanisms.Two analytical fatigue models are proposed. The first one concerns the effect of the loaded volume on the uniaxial fatigue strength of the porosity containing alloys using an approach to predict of the maximum pore size in a given volume. The second model, based on a probabilistic approach, takes into account the competition between the different observed damage mechanisms and leads to a Kitagawa-Takahashi type diagrams for different loading modes. It is shown that these analytical models result in good predictions for the three materials investigated and the four loading modes.A numerical study, presented in the last section, is related to the 3D finite element analysis of real pores. Real pore geometries are obtained thank to micro-tomography observations. The principal aim of this study is to evaluate the possibility of predicting the fatigue strength at the macroscopic scale thanks to the local mechanical behaviour around critical pores.Ces travaux de thèse concernent l’effet des hétérogénéités microstructurales sur la tenue en fatigue multiaxiale à grand nombre de cycles (FGNC) d’alliages d’Al-Si de fonderie utilisés dans un contexte automobile. Les hétérogénéités microstructurales caractéristiques de cette famille de matériau sont la matrice d’aluminium (souvent caractérisée à l’aide la DAS et/ou la SDAS et du niveau de durcissement par précipitation), les inclusions (particules de silicium, intermétalliques) et les défauts de fonderie (films d’oxyde et surtout porosités).Afin de découpler clairement ces effets, trois nuances d’alliages d’aluminium de fonderie obtenues à l’aide de différents procédés (coulée en coquille, coulée par procédé à moule perdu) et associées à plusieurs traitements thermiques (T7, Compression isostatique à chaud (CIC)) ont été étudiées. Le traitement CIC a en particulier été employé afin d’obtenir une microstructure exempte de pore. Une vaste campagne d’essais en FGNC a été conduite pour quatre modes de chargement : uniaxial (R=-1), torsion (R=-1), traction-torsion combinées (R=-1) et traction équibiaxiale (R=0.1). Les effets sur le comportement en FGNC ont été identifiés pour les matériaux avec et sans pores : effet de la multiaxialité pour les chargements à R=-1, effet de la contrainte moyenne et effet de la biaxialité en traction biaxiale à R=0.1. Une attention particulière a été portée à la caractérisation des mécanismes d’endommagement dans l’objectif de mettre en évidence le role des pores, de la matrice d’aluminium, des inclusions dans les mécanismes d’endommagement, et ceci pour les différentes modes de chargement.Deux approches analytiques ont ensuite été proposées. La première concerne la modélisation de l’effet de volume sollicité sur la tenue en fatigue sous chargement uniaxial en présence de pore en se basant sur une approche de prédiction de la taille maximale de pore dans un volume donné. La seconde, basée sur une approche probabiliste, est dédiée à la simulation du diagramme de Kitagawa-Takahashi pour différents modes de chargement. Ces deux approches conduisent à des résultats en accord avec l’expérience, ceci pour les différents matériaux et conditions étudiées.La dernière partie propose une analyse 3D par éléments finis de l’effet des pores sur la résistance en fatigue. L’analyse repose sur l’utilisation de la géométrie réelle des pores, obtenue à l’aide d’observations en micro-tomographie RX 3D. Ce travail a pour but d’évaluer la possibilité de prédire la limite de fatigue à l’échelle macrosopique à partir de la réponse mécanique "locale" au voisinage des pores critiques

Localization in Sensor Networks with Fading Channels based on Nonmetric Distrance Models

Wireless Sensor Network (WSN) applications nowadays are an emerging avenue in which sensor localization is an essential and crucial issue. Many algorithms have been proposed to estimate the coordinate of sensors in WSNs, however, the attained accuracy in real-world applications is still far from the theoretical lower bound, Crame-Rao Lower Bound (CRLB), due to the effects of fading channels. In this paper, we propose a very simple and light weight statistical model for rang-based localization schemes, especially for the most typical localization algorithms based on received signal strength (RSS) and time-of-arrival (TOA). Our proposed method infers only the order or the nomination of given distances from measurement data to avoid significant bias caused by fading channels or shadowing. In such way, it radically reduces the effects of the degradation and performs better than existing algorithms do. With simulation of fading channels and irregular noises for both the RSS-based measurement and the TOA-based measurement, we analyze and testify both the benefits and the drawbacks of the proposed models and the localization scheme

Towards Opportunistic Data Dissemination in Mobile Phone Sensor Networks

Recently, there has been a growing interest within the research community in developing opportunistic routing protocols. Many schemes have been proposed; however, they differ greatly in assumptions and in type of network for which they are evaluated. As a result, researchers have an ambiguous understanding of how these schemes compare against each other in their specific applications. To investigate the performance of existing opportunistic routing algorithms in realistic scenarios, we propose a heterogeneous architecture including fixed infrastructure, mobile infrastructure, and mobile nodes. The proposed architecture focuses on how to utilize the available, low cost short-range radios of mobile phones for data gathering and dissemination. We also propose a new realistic mobility model and metrics. Existing opportunistic routing protocols are simulated and evaluated with the proposed heterogeneous architecture, mobility models, and transmission interfaces. Results show that some protocols suffer long time-to-live (TTL), while others suffer short TTL. We show that heterogeneous sensor network architectures need heterogeneous routing algorithms, such as a combination of Epidemic and Spray and Wait