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In recent years, Multi-hop Wireless Networks (MHWNs) have experienced an explosion of deployment due to the increasing demand for continuous connectivity regardless of the physical location. Internet predominant transport protocols, i.e. Transmission Control Protocol (TCP), face performance degradation in MHWNs because of the high loss and link failure rates. Several solutions have been proposed which are based on network state estimation or use information from MAC layer (called metrics) in a cross-layer manner to better comprehend the network state. The first part of this thesis provides a survey and comprehensive definition of common metrics from Physical, MAC, Network and Transport layers and thus provides a multi-criteria and hierarchical classification. After that, the effectiveness in reflecting network information of MAC metrics is also investigated in a systematic way by simulating various network situations and measuring the MAC metrics. Thus, the good MAC metric for congestion control which is coupled with the network contention level and the medium induced losses will be found out. From the results of the effectiveness study, new rate control schemes for transport protocols are proposed which adapt efficiently the source bit rate depending on the network condition provided by some MAC metrics. Through an extensive set of simulations, the performance of the proposed rate control schemes in MHWNs is investigated thoroughly with several network situations.

In this study the effects of age (18-55 years), differing levels of fitness (VO 2max ranging from 35.5 to 68.8ml.kg-1.min-1) and endurance training (10 weeks) on heart rate control were investigated. Fitness level was initially determined by a VO2max stress test, succeeded by cold hand and cold face pressor test of autonomic activity. Following these baseline measurements, the subjects (32 nonsmoking male volunteers) were endurance-trained three to four times a week for a 10-week period. The baseline tests were readministered following the 10-week dynamic exercise training period. These data suggest that a natural consequence of aging is a diminishment of autonomic heart rate control; however, endurance training appears to interrupt the aging influence. Individuals of low fitness level appear to have heart rate control dominated by the sympathetic system, while individuals with high fitness levels have a vagally dominated heart rate control system.

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic.

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic.

Waterflood optimization via rate control is receiving increased interest because of rapid developments in the smart well completions and I-field technology. The use of inflow control valves (ICV) allows us to optimize the production/injection rates of various segments along the wellbore, thereby maximizing sweep efficiency and delaying water breakthrough. It is well recognized that field scale rate optimization problems are difficult because they often involve highly complex reservoir models, production and facilities related constraints and a large number of unknowns. Some aspects of the optimization problem have been studied before using mainly optimal control theory. However, the applications to-date have been limited to rather small problems because of the computation time and the complexities associated with the formulation and solution of adjoint equations. Field-scale rate optimization for maximizing waterflood sweep efficiency under realistic field conditions has still remained largely unexplored. We propose a practical and efficient approach for computing optimal injection and production rates and thereby manage the waterflood front to maximize sweep efficiency and delay the arrival time to minimize water cycling. Our work relies on equalizing the arrival times of the waterfront at all producers within selected sub-regions of a water flood project. The arrival time optimization has favorable quasi-linear properties and the optimization proceeds smoothly even if our initial conditions are far from the solution. We account for geologic uncertainty using two optimization schemes. The first one is to formulate the objective function in a stochastic form which relies on a combination of expected value and standard deviation combined with a risk attitude coefficient. The second one is to minimize the worst case scenario using a min-max problem formulation. The optimization is performed under operational and facility constraints using a sequential quadratic programming approach. A major advantage of our approach is the analytical computation of the gradient and Hessian of the objective which makes it computationally efficient and suitable for large field cases. Multiple examples are presented to support the robustness and efficiency of the proposed optimization scheme. These include several 2D synthetic examples for validation purposes and 3D field applications.

<p> Cooperative haptics enables multiple users to manipulate computer simulated objects in a shared virtual environment and to feel the presence of other users. Prior research in the literature has mainly addressed single user haptic interaction. This thesis is concerned with haptic simulation in multi-user virtual environments in which the users can interact in a shared virtual world from separate workstations over Ethernet-based Local Area Networks (LANs) or Metropolitan Area Networks (MANs). In practice, the achievable real-time communication rate using a typical implementation of network protocols such as the UDP and TCP/IP can be well below the 1kHz update rate that is suggested in the literature for high fidelity haptic rendering. However by adopting a multi-rate control strategy as proposed in this work, the local control loops can be executed at 1kHz while the data packet transmission between the user workstations occur at a lower rate. Within such a framework, two control architectures, namely centralized and distributed are presented. In the centralized controller a central workstation simulates the virtual environment, whereas in the distributed controller each user workstation simulates its own copy of the virtual environment. Two different approaches have been proposed for mathematical modeling of the controllers and have been used in a comparative analysis of their stability and performance. The results of such analysis demonstrate that the distributed control architecture has greater stability margins and outperforms the centralized controller. They also reveal that the limited network transmission rate can degrade the haptic fidelity by introducing viscous damping into the virtual object perceived impedance. This extra damping is compensated by active control based on the damping values obtained from the analytical results. Experimental results conducted with a dual-user/dual-finger haptic platform are presented for each of the proposed controller under various scenarios in which the user workstations communicate with UDP protocol subjected to a limited transmission rate. The results demonstrate the effectiveness of the proposed distributed architecture in providing a stable and transparent haptic simulation in free motion and in contact with rigid environments.</p> / Thesis / Master of Applied Science (MASc)

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Ces dernières années, les réseaux multi-sauts sans fil (MHWNs) ont connu une explosion de déploiement en raison de la demande croissante de connectivité continue indépendamment de l'emplacement physique. Les protocoles de transport Internet prédominantes, c.-à-Transmission Control Protocol (TCP), se trouvent face à la dégradation des performances dans MHWNs en raison de les taux élevés de pertes et de défaillance du lien. Plusieurs solutions ont été proposées qui sont basées sur l'estimation de l'état du réseau ou sur l'utilisation de renseignements de la couche MAC (dénommée métriques) dans une manière d’inter-couche pour mieux comprendre l'état du réseau. La première partie de cette thèse fournit une enquête et la définition complète de métriques communs des couches physique, MAC, réseau et transport et fournit ainsi un multi-critères et la classification hiérarchique. Après cela, l'efficacité dans la réflexion des informations de réseau des métriques de la couche MAC est également étudiée dans une façon systématique en simulant des situations différents de réseau et de mesurer les métriques de la couche MAC. Ainsi, le bonne MAC métrique pour le contrôle de congestion qui est couplé avec le niveau de contention de réseau et les pertes provoquées moyen sera découvert. D'après les résultats de l'étude sur l'efficacité, deux nouveaux systèmes de contrôle de débit pour les protocoles de transport sont proposés qui s'adaptent efficacement le débit de source en fonction de l'état du réseau fournie par certains métriques MAC. Grâce à un vaste ensemble de simulations, les performances des systèmes proposées de contrôle de débit dans MHWNs sont examinées approfondie avec des situations de réseau. / In recent years, Multi-hop Wireless Networks (MHWNs) have experienced an explosion of deployment due to the increasing demand for continuous connectivity regardless of the physical location. Internet predominant transport protocols, i.e. Transmission Control Protocol (TCP), face performance degradation in MHWNs because of the high loss and link failure rates. Several solutions have been proposed which are based on network state estimation or use information from MAC layer (called metrics) in a cross-layer manner to better comprehend the network state. The first part of this thesis provides a survey and comprehensive definition of common metrics from Physical, MAC, Network and Transport layers and thus provides a multi-criteria and hierarchical classification. After that, the effectiveness in reflecting network information of MAC metrics is also investigated in a systematic way by simulating various network situations and measuring the MAC metrics. Thus, the good MAC metric for congestion control which is coupled with the network contention level and the medium induced losses will be found out. From the results of the effectiveness study, new rate control schemes for transport protocols are proposed which adapt efficiently the source bit rate depending on the network condition provided by some MAC metrics. Through an extensive set of simulations, the performance of the proposed rate control schemes in MHWNs is investigated thoroughly with several network situations.