Cette thèse analyse la possibilité d'utiliser des communications sans fil inter-véhiculaires pour améliorer la sécurité routière. Les performances du nouveau réseau ainsi créé (réseau ad-hoc véhiculaire) sont étudiées analytiquement et par des simulations dans un environnement réaliste. La thèse se concentre surtout sur des scénarios avec une forte densité de véhicules. Dans ce cas, l'accès au support devient un problème essentiel, en principal pour les applications de sécurité routière qui nécessitent une qualité de service élevée pour fonctionner dans un tel contexte. Ce travail montre que la version actuelle du standard IEEE 802.11, proposé comme méthode d'accès dans les réseaux véhiculaires, ne peut pas résoudre ce problème de passage à l'échelle pour supporter correctement les applications de sécurité routière. Plusieurs améliorations possibles sont analysées, liées à l'utilisation optimale de certains paramètres du protocole comme la taille de la fenêtre de contention ou bien le seuil de détection de la porteuse. Des nouveaux mécanismes adaptatifs visant ces paramètres sont proposés et les améliorations ainsi obtenues sont non-négligeables. Finalement, une nouvelle méthode d'accès est définie, en tenant compte des caractéristiques des applications de sécurité routière. Toujours basée sur des techniques CSMA, cette technique donne des résultats largement supérieurs à la version standard actuelle. / The equipment of vehicles with wireless communication devices in order to improve road safety is a major component of a future intelligent transportation system. The success and availability of IEEE 802.11-based products make this technology the main competitor for the Medium Access Control (MAC) layer used in vehicle-to-vehicle communication. The IEEE 802.11p amendment has been specially designed in this special context of wireless access in vehicular environments. However, as all the other approaches based on Carrier Sense Multiple Access (CSMA), this protocol presents scalability problems, which leads to poor performance in high density scenarios, quite frequent in the case of a vehicular ad hoc network (VANET). This thesis studies the congestion control problem in the context of safety vehicular communications, with a special focus on the back-off mechanism and the carrier sense function. First of all, a number of important characteristics presented by the safety messages are discovered and understood by the means of an analytical framework. Second, the lessons learned from the analytical study are put into practice with the design of two adaptive mechanisms (one for the contention window and the other one for the carrier sense threshold) that take into account the local vehicular density. These mechanisms remain simple, but highly efficient, while also being straightforward to integrate in IEEE 802.11 devices. Finally, by taking into account the most important properties of a safety VANET, a new CSMA-based MAC protocol is proposed. This new access method, named Safety Range CSMA (SR-CSMA), relies on the idea that collisions can not be avoided in a high density network. However, by increasing the number of simultaneous transmissions between geographically distant nodes, SR-CSMA manages to better protect the immediate neighborhood, the most important area for safety applications.

Notre recherche interroge les modalités selon lesquelles une pratique artistique peut constituer un vecteur de contestation en contexte autoritaire. Elle se situe à l’intersection de deux aires de questionnement. D’une part, elle examine les multiples rapports qu’un monde de l’art peut entretenir avec un monde politique, éclairant les enjeux politiques qui traversent un champ cinématographique fortement dépendant de l’État, ainsi que les pratiques contestataires spécifiques qui y ont court. D’autre part, elle explore des formes de contestation qui se déploient à la marge d’un espace politique verrouillé, mettant au jour certains mécanismes de l’autoritarisme observés dans les négociations, arrangements et conflits entre acteurs du monde cinématographique et acteurs de l’appareil bureaucratique et étatique. Dans un premier temps, nous montrons comment les relations sociales qui se tissent autour de l’organisation et du fonctionnement de la production cinématographique polarisent et réfractent certaines pratiques et enjeux spécifiques au champ politique tout en les reformulant. Nous plaçons ensuite l’analyse au cœur des films afin de repérer et de décrire, à partir des différents procédés propres au langage cinématographique, des thématiques, des catégories et des objets qui relèvent du politique, sur lesquels les cinéastes posent un regard critique, alors même que l’expression d’une opinion contestataire dans l’espace public s’avère problématique / Our research investigates how an artistic activity can also be a vehicle for contention within an authoritarian context. It relies at the crossroad of two areas of questioning. On the one hand, we explore the various interactions between an art world and a political world, shedding light on the political logics at stake in a cinematographic field greatly dependent upon the state, as well as on the contentious practices emerging from this particular configuration. On the other hand, we scrutinize contention expressed at the margin of a locked political space, unveiling some mechanisms of authoritarianism produced by negotiations, arrangements and conflicts between actors belonging to the cinematographic world and actors of the bureaucratic apparatus. At first, we examine how the social relationships woven around the organization and the functioning of film production polarize and refract practices and issues proper to the political field while reformulating them. Then we shift the focus of our analysis on the very heart of the films to locate and describe, from the specific tools of the film language, subjects, categorizations and objects dealing with politics, upon which filmmakers cast a critical eye, whereas contentious expression in the public sphere proves to be problematic

La Police Nationale est l’une des professions les plus syndiquées en France, avec un taux de syndicalisation proche des 70%. Pourtant, les recherches sur le militantisme et les mouvements sociaux pensent souvent les policiers comme les instruments de la répression, comme le bras armé de l’État, mais bien plus rarement comme des travailleurs soumis, comme d’autres, à des pressions de leur hiérarchie et à des difficultés professionnelles. A partir de ce constat, et grâce à une enquête socio-ethnographique, cette thèse questionne l’organisation et le fonctionnement du syndicalisme policier. Après une mise en perspective historique permettant de présenter les modalités de construction et d’évolution du syndicalisme policier, l’analyse porte sur le travail syndical de représentation et le rapport au politique. Nous montrons ainsi que les syndicalistes policiers articulent un important travail de service aux adhérents (en participant notamment aux commissions administratives paritaires qui gèrent les carrières des fonctionnaires) et des formes de mobilisations plus conflictuelles. Comme dans d’autres milieux, les syndicalistes policiers sont soumis à une logique de professionnalisation, mais les permanents syndicaux sont accompagnés, dans leur travail, par un important réseau de militants et délégués qui contribuent à entretenir la proximité avec les travailleurs. En mobilisant et en questionnant le concept bourdieusien de champ, nous interrogeons enfin les relations entre le champ syndical policier et le champ politique. Les syndicalistes policiers entretiennent un rapport ambivalent et très circonstancié au politique, entre rejet, mise à distance et appropriation. Notre démarche ethnographique permet de saisir les logiques de différenciation des pratiques en fonction des acteurs, et plus particulièrement en fonction du niveau de responsabilité. Ainsi, si l’évitement du politique est la règle générale, elle est appliquée avec bien plus de rigueur au niveau départemental qu’au niveau national. / The French National Police force is one of the most unionised professions in the country: close to 70%. Yet most of the scientific research on activism and social movements only considers police officers as a entities within the state repression system, and rarely as workers who experience, as any others, pressures from their management and professional struggles. Based on these observations, and using a socio-ethnographic survey, our thesis aims to question the organization and running of French police unionism. After a brief analysis of the historical process of construction and evolution of police unionism, we examine the unions representation work and its relation to politics.We notably demonstrate that police unionists articulate an important work of service to their paying members (by participating in the joint administrative commissions which manage the careers of civil servants) and forms of more conflicting mobilizations. As in other environments, police unionists are subject to a logic of professionalization, but the union officials are accompanied in their work by a large network of activists and representatives who contribute to maintaining proximity with the workers.Mobilizing and questioning Bourdieu's concept of “field”, we finally examine the relations between the police union field and the political field. Police unionists entertain an ambivalent and very circumstantial relationship to politics, caught between rejection, distanciation and appropriation. Our ethnographic approach allows us to grasp the logic of practice differentiation by stakeholder, and more particularly by level of responsibility. Thus, if avoiding politics is the general rule, it is applied much more rigorously at the local level than at the national level.

In Intelligent Transportation Systems (ITS), disseminating warning messages in a timely and efficient way through wireless short-range communications can save many lives and reduce traffic congestion. A geographical broadcast protocol provides data delivery to specified geographical areas, using multi-hop communications if needed. Among the main challenges for such protocols are forwarder selection and the reduction of the number of hops required to reach and cover the destination area.  In this thesis we propose an efficient geographical broadcast protocol called Preferred and Contention Based Forwarding (PCBF) and evaluate it through simulations. PCBF uses a combination of contention-based forwarding and selecting preferred forwarders also found in other protocols like Emergency Message Dissemination for Vehicular Environments (EMDV). Since the preferred forwarder is allowed to immediately forward the packet (evading contention among other potential forwarders), this approach reduces end-to-end delays. Notable extensions of PCBF compared to EMDV are the use of direct negative acknowledgements in case of unnecessary rebroadcasts and the use of forwarders outside the target region.  Our simulation results show that the PCBF protocol outperforms selected other protocols in terms of end-to-end delay, re-broadcast overhead and reliability in both sparse and dense networks.

The IEEE 802.15.4 standard is a low-power, low-rate MAC/PHY standard that meets most of the stringent requirements of single-hop wireless sensor networks. Sensor networks with nodal populations comprised of thousands of devices have been envisioned in conjunction with environmental, vehicular, and military applications, to mention a few. However, such large sensor network deployments necessitate multi-hop support as well as low power consumption. In light of the standard's extremely limited joint support of the two aforementioned attributes, this thesis presents two essential contributions. First, a framework is proposed to implement a new IEEE 802.15.4 operating mode, namely the synchronized peer-to-peer mode. This mode is designed to enable the standard's low-power features in peer-to-peer multi-hop-ready topologies. The second contribution is a distributed Guaranteed Time Slot (dGTS ) management scheme designed to function in the newly devised network mode. This protocol provides reliable contention-free access in peer-to-peer topologies in a completely distributed manner. Assuming optimal routing, our simulation experiments reveal perfect delivery ratios as long as the traffic load does not reach or surpass its saturation threshold. dGTS sustains at least twice the delivery ratio of contention access under sub-optimal dynamic routing. Moreover, the dGTS scheme exhibits minimum power consumption by eliminating the retransmissions attributed to contention, which in turn reduces the number of transmissions to a minimum. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-10-25 14:55:36.811

Security and privacy are among the growing concerns of a Vehicular Ad hoc Network (VANET) which requires a high degree of liability from its participants. In this dissertation, We address security, anonymity and privacy challenges of VANETs in the light of the IEEE standards for vehicular communications. VANET provides a variety of road-safety and other applications through wireless devices installed in vehicles and roadside infrastructure. A roadside infrastructure in VANET is generally public, and is prone to several different malicious attacks including node compromise, impersonation, and false message delivery attacks. Therefore, a user of a VANET must verify the integrity of a message that is delivered from a roadside infrastructure. On the other hand, a vehicle-originated message should be anonymous in order to ensure user-privacy in a VANET. However, a vehicle must not be able to take advantage of its anonymity for any misbehavior like sending false messages or malicious updates to other vehicles or a roadside infrastructure. We use proxy signature, identity-based signature, and elliptic curve cryptosystems to provide authentication for infrastructure generated messages, and anonymous authentication for vehicle originated messages. Authentication in a dense traffic condition is a challenge for a receiving entity as it incurs a processing delay at the receiving end. We address this issue with a dynamic approach that selectively verifies received messages based on a message's MAC-layer priority and a sender's information relevance. This approach makes a trade-off between priority and fairness in vehicular message authentication. We develop a network simulator to measure the impact of our authentication schemes over a WAVE protocol stack. Also, we investigate how some of the MAC-layer weaknesses may impair the security of a VANET. Our solutions are lightweight, bandwidth friendly and compatible to the current standards of vehicular communications.

Security and privacy are among the growing concerns of a Vehicular Ad hoc Network (VANET) which requires a high degree of liability from its participants. In this dissertation, We address security, anonymity and privacy challenges of VANETs in the light of the IEEE standards for vehicular communications. VANET provides a variety of road-safety and other applications through wireless devices installed in vehicles and roadside infrastructure. A roadside infrastructure in VANET is generally public, and is prone to several different malicious attacks including node compromise, impersonation, and false message delivery attacks. Therefore, a user of a VANET must verify the integrity of a message that is delivered from a roadside infrastructure. On the other hand, a vehicle-originated message should be anonymous in order to ensure user-privacy in a VANET. However, a vehicle must not be able to take advantage of its anonymity for any misbehavior like sending false messages or malicious updates to other vehicles or a roadside infrastructure. We use proxy signature, identity-based signature, and elliptic curve cryptosystems to provide authentication for infrastructure generated messages, and anonymous authentication for vehicle originated messages. Authentication in a dense traffic condition is a challenge for a receiving entity as it incurs a processing delay at the receiving end. We address this issue with a dynamic approach that selectively verifies received messages based on a message's MAC-layer priority and a sender's information relevance. This approach makes a trade-off between priority and fairness in vehicular message authentication. We develop a network simulator to measure the impact of our authentication schemes over a WAVE protocol stack. Also, we investigate how some of the MAC-layer weaknesses may impair the security of a VANET. Our solutions are lightweight, bandwidth friendly and compatible to the current standards of vehicular communications.

No description available.

In this thesis, we are concerned with content dissemination in mobile ad hoc networks. The scope of content dissemination is limited by network capacity, and sometimes the price to be paid for securing faster delivery. In the first part of the thesis, we address the issue of finding the maximum throughput that a mobile ad-hoc network can support. We have assumed that there is no price involved, and all nodes work as a team. The problem of determining the capacity region has long been known to be NP-hard even for stationary nodes. Mobility introduces an additional dimension of complexity because nodes now also have to decide when they should initiate route discovery. Since route discovery involves communication and computation overhead, it should not be invoked very often. On the other hand, mobility implies that routes are bound to become stale, resulting in sub-optimal performance if routes are not updated. We attempt to gain some understanding of these effects by considering a simple one-dimensional network model. The simplicity of our model allows us to use stochastic dynamic programming (SDP) to find the maximum possible network throughput with ideal routing and medium access control (MAC) scheduling. Using the optimal value as a benchmark, we also propose and evaluate the performance of a simple threshold-based heuristic. Unlike the optimal policy which requires considerable state information, the proposed heuristic is simple to implement and is not overly sensitive to the threshold value. We find empirical conditions for our heuristic to be near-optimal. Also, network scenarios when our heuristic does not perform very well are analyzed. We provide extensive numerical analysis and simulation results for different parameter settings of our model. Interestingly, we observe that in low density network the average throughput can first decrease with mobility, and then increase. This motivates us to study a mobile ad-hoc network when it is sparse and in a generalized environment, such as when movement of nodes is in a two-dimension plane. Due to sparseness, there are frequent disruptions in the connections and there may not be any end-to-end connection for delivery. The mobility of nodes may be used for carrying the forwarded message to the destination. This network is also known as a delay tolerant network. In the rest part of the thesis, we consider the relay nodes to be members of a group that charges a price for assisting in message transportation. First, we solve the problem of how to select first relay node when only one relay node can be chosen from a given number of groups. Next, we solve two problems, namely price-constrained delay minimization, and delay-constrained price optimization.

Submitted by Rafael Murta Reis (murtarafa@gmail.com) on 2016-04-04T14:05:24Z No. of bitstreams: 1 Dissertação_MURTA_REIS_RAFAEL.pdf: 4830215 bytes, checksum: 0222cbb2739e7a08b4ce15e4ccc31234 (MD5) / Approved for entry into archive by Pamela Beltran Tonsa (pamela.tonsa@fgv.br) on 2016-04-04T14:11:22Z (GMT) No. of bitstreams: 1 Dissertação_MURTA_REIS_RAFAEL.pdf: 4830215 bytes, checksum: 0222cbb2739e7a08b4ce15e4ccc31234 (MD5) / Made available in DSpace on 2016-04-04T14:14:24Z (GMT). No. of bitstreams: 1 Dissertação_MURTA_REIS_RAFAEL.pdf: 4830215 bytes, checksum: 0222cbb2739e7a08b4ce15e4ccc31234 (MD5) Previous issue date: 2016-02-29 / The research is intended to study public government conducts during the 20th Edition of the FIFA World Cup, occurred in Brazil in 2014. The sports mega-event was surrounded by contradictions, and was publicly contested by thousands of Brazilians, especially with regards to the high amount of public spending and FIFA's (Fédération Internationale de Football Association) considerable profits. During the preparations and the event, Brazil experienced one of the longest cycle of contention in its recent history, highlighting the feeling of dissatisfaction held by many Brazilians with regards to the expenses incurred by federal, state and municipal governments in order to host the games. Focusing mainly on the mega-event management in the city of São Paulo, the study sought to understand the agreement between the parties, and analyze the relationship between the institutions – FIFA and Governments – in the operationalization and decisions regarding the mega-event. Moreover, the study highlights the interfaces established between governments and the civil society, with its empirically identified diversity, and the impacts of its claims on São Paulo's municipal government management. Results show the emergence of antagonistic relations between such groups of interest as well as between different social actors. Additionally, the World Cup in Brazil did not present optimal levels of transparency and public participation, even though some efforts towards these goals were identified. Finally, some of the consequences of the public protests on governmental action can be seen through the use of violence and repression by the police in order to deal with a scenario of multiple protests. Since this study is unique, the research was conducted by qualitative methods. Multiple sources were used during the gathering process which turned possible data triangulation and increased results validity. Direct observations were made during the protests and at the World Cup enterprises’ influence zone. Also official documents, legislations, minutes and press news were analyzed and interviews were conducted with key-actors from federal and municipal governments, activists, protestors, communities’ leaders and society delegates. The survey showed that mega sporting events are an important research topic around the world, and have shown to be a relevant concern in developing countries, as well as have become an important policy tool for promoting the image of host countries overseas and the projection of parties in national territories. Their results highlight the formation of antagonist fields between governments and civil society, and the formation of conflict arenas also among the social actors. Although there have been seen some efforts for the transparency of management, one could not say that the World Cup in Brazil has had ideal level of transparency, neither of social participation. On the one hand there have had efforts to improve transparency, on the other the social participation channels set have not expressed relevance to public management of the mega event. The interfaces between governments and civil society have been identified, as well as their effects and inflections on the management of the World Cup. The main interface highlighted occurred at street level and expressed itself in the confrontations between demonstrators and police. The second most obvious one was consolidated in direct negotiation between communities that were vulnerable to the works of the World Cup and municipal managers. The effects of street protests on the action of governments stood out in police activity, using violence and repression as the main response to the demonstrations, which became most evident in the protests “There Will Not Be World Cup”, and the creation of spaces for direct negotiation with communities, this one influenced more directly by the formation of claim groups, such as the People's Committee of the World Cup, and resistance by the community. The World Cup management in Brazil was complex and showed in the perspective of federative relations some problems between city, state and union, which deals with the coordination of programs, policies or actions, in this case, a mega sports event, of shared management. The case clearly showed dissonances and misalignments between federal, state and municipal government on the practices of dialogue, negotiation, transparency and social participation. The research highlights the formation of a more watchful, critical and politicized social group, which claims, disputes and occupies the streets demonstrating their dissatisfaction with governments, political systems and forms of representation. Points to more tangible results and more harmonious relations between governments and population when alternative forms of social participation and involvement are implemented, particularly spaces and processes where there is room for negotiation and inclusion of civil society in decision-making / Esta pesquisa se propôs a investigar a gestão pública da 20ª edição da Copa do Mundo FIFA, realizada no Brasil em 2014. Contestada popularmente por milhares de brasileiros, o megaevento esportivo teve suas contradições, principalmente em relação aos altos gastos públicos e à lucrativa participação da Federação Internacional de Futebol (FIFA). Durante os seus preparativos e realização, aconteceu um dos mais duradouros ciclos de protestos da história recente do Brasil, o que destaca a insatisfação de muitos brasileiros em relação aos investimentos dos governos federal, estaduais e municipais para a sua realização. Com recorte mais aprofundado para a gestão do megaevento na cidade de São Paulo, o trabalho procurou compreender os acordos entre as partes e analisar a relação entre as instituições – a FIFA e os Governos – na operacionalização e decisões sobre o megaevento. Além disso, destaca as interfaces estabelecidas entre governos e a sociedade civil, em sua diversidade identificada empiricamente, e aprofunda nas inflexões das reivindicações populares e protestos na gestão do megaevento pela prefeitura paulistana. O estudo é um estudo de caso único e, portanto, foi realizado com métodos qualitativos de pesquisa. Foram utilizadas fontes múltiplas de coleta que possibilitaram a triangulação dos dados obtidos e o aumento da validade dos resultados. Foram feitas observações diretas durante os protestos e na região de impacto dos empreendimentos da Copa, coleta em documentos oficiais, legislações, atas, contratos e matérias jornalísticas e entrevistas com atores-chave dos governos federal e municipal, com ativistas e manifestantes, líderes comunitários e representantes de organizações da sociedade civil. A pesquisa apontou que os megaeventos esportivos são um importante tema de pesquisa pelo mundo e têm se revelado como uma relevante preocupação em países em desenvolvimento, além de terem se tornado um importante instrumento político para a promoção da imagem dos países-sede no exterior e para a projeção de partidos nos territórios nacionais. Seus resultados destacam a formação de campos antagônicos entre governos e sociedade civil e a formação de arenas de conflito também entre os atores sociais. Embora haja visto alguns esforços pela transparência da gestão, não se pode dizer que a Copa do Mundo no Brasil teve nível ideal de transparência, tampouco de participação social. Se por um lado houve esforços para se aprimorar a transparência, por outro, os canais de participação social instituídos não expressaram relevância para a gestão pública do megaevento. As interfaces entre governos e a sociedade civil foram identificadas, assim como seus efeitos e inflexões sobre a gestão do mundial. A principal interface destacada se deu no nível da rua e se afirmou na forma do enfrentamento entre manifestantes e a polícia. A segunda mais evidente se consolidou na negociação direta entre comunitários vulneráveis às obras da Copa e gestores municipais. Os efeitos dos protestos de rua sobre a ação dos governos se destacou na atividade policial, que usou a violência e a repressão como principais respostas ao conjunto de manifestações, e na criação de espaços de negociação direta com as comunidades, este influenciado mais diretamente pela formação de grupos de reivindicação, como o Comitê Popular da Copa, e pela resistência da própria comunidade. A gestão da Copa do Mundo no Brasil foi complexa e evidenciou, do ponto de vista das relações federativas, alguns problemas entre município, estado e União, que tratam da coordenação de programas, políticas ou ações, neste caso, um megaevento esportivo, de gestão compartilhada. O caso aponta dissonâncias e desalinhamentos entre governo federal, estadual e municipal sobre as práticas de diálogo, negociação, transparência e participação social. A pesquisa destaca a formação de um conjunto social mais atento, crítico e politizado, que reivindica, contesta e ocupa as ruas demonstrando sua insatisfação com governos, sistemas políticos e formas de representação. Aponta para resultados mais tangíveis e relações mais harmônicas entre governos e população quando são implementadas formas alternativas de participação e envolvimento social, sobretudo espaços e processos em que há lugar para a negociação e inserção da sociedade civil nos processos decisórios