Dans les systèmes Store and Forward (S&F), le routage comme moyen d'optimisation a été largement étudie mais aucune règle générale n'a pu être établie. Des paramètres et des méthodes d'évaluation spécifiques à ces systèmes n'ont pas encore été définis. Jusqu'à présent seuls des critères appartenant aux réseaux traditionnels étaient utilises (temps, longueur de la route). Or la tolérance aux délais du réseau s&f minimise l'importance de ces critères. De ce fait, pour ces systèmes, il est nécessaire d'employer des mécanismes et des critères mieux adaptent à leurs caractéristiques. Cette étude a pour but de montrer que le routage dans les systèmes s&f peut être aborde a partir de perspectives nouvelles. Pour ce faire, nous utilisons une politique de routage pré calcule depuis la source. Nous présentons un état de l'art sur les systèmes s&f, leurs mécanismes et leurs scénarios d'application. Nous proposons un outil de calcul de routes pour un scenario de communications par satellite compose par deux constellations. Cet instrument est conçu à partir des techniques utilisées dans les systèmes de transport. Nous proposons ensuite un ensemble de nouvelles métriques pour le routage dans les systèmes s&f. Ces métriques permettent de caractériser le système s&f à partir de leur nature propre et d'établir des politiques de routage mieux adaptées à leurs conditions de fonctionnement. Enfin nous présentons les développements possibles dans cette thématique

This research investigated the need, design, and evaluation of a product capable of providing support to forward-leaning postures. Due to the high occurrence of low-back pain in industry potentially due to workers performing their tasks while assuming forward-leaning postures, along with the biological plausibility of these postures causing low-back pain, the need was established for a product that provides forward-leaning support. An envelope was quantified, ranging from the 5th percentile female to the 95th percentile male, to establish the range of potential forward-leaning postures. The design of a Support-Arm for use with current ergonomic chairs was discussed and design feature specifications were then provided. A Latin Square statistical design was employed to evaluate a Support-Arm model alongside 8 other commonly used chairs over 3 different postures. Subjects, overall, had lower peak pressures for the buttock-thigh region, increased productivity, higher comfort levels, and higher buttock-thigh contact areas when seated in the Support-Arm model chair as compared to the other chairs. Subjects, overall, also ranked this chair first over the other chairs for preferred use after having sitting experience in all 9 chairs. In an additional part of the evaluation, subjects chose their own set-up of the Support-Arm model chair. Eleven of the 18 subjects chose to use the Support-Arm when their workstation was located 36” above the floor. Subjects confirmed the need to design a Support-Arm capable of providing forward leaning support to the entire envelope of forward-leaning postures. Statistical evaluation revealed several significant differences between the chairs. The results gave no indication that the use of a Support-Arm for forward-leaning support may cause detrimental effects to users or overall chair ergonomics. Future research could track workers’ use of a Support-Arm in industry and compare their occurrence of low-back pain to a control group.

This research examines a two-way relay network consisting of two transceivers and multiple parallel relays, which are equipped with single antennas and operate in a halfduplex mode. In this system, the two transceivers prefer to exchange their information via relays. It is assumed that the relays have the full instantaneous channel state information (CSI) and relay the signals using the amplify-and-forward (AF) method. The performance of two AF bi-directional network beamforming schemes, namely multiple access broadcast channel (MABC) strategy and time division broadcast channel (TDBC) protocol, under joint optimal power control and beamforming design are studied and compared. To do so, we first design a TDBC-based bi-directional network beamformers, through minimization of the total power consumed in the whole network subject to quality of service (QoS) constraints, for the case with a direct link between the two transceivers. The corresponding power minimization problem is carried out over the transceiver transmit powers as well as relay beamforming weights, thus resulting in a jointly optimal power allocation and beamforming approach. We devise optimal secondorder cone programming based solutions as well as fast gradient-based solutions to these problems. Then these solutions are exploited to compare the performance of the underlying TDBC-based approach to that of the MABC-based technique developed in [1]. This comparison is important because the TDBC approach appears to have certain advantages which can be exploited towards improving the performance of two-way network beamforming. These advantages include the additional degree of freedom as well as the possibility of benefitting from the availability of a direct link between the two transceivers. Interestingly, in the absence of a direct link between the two transceivers, we show that when the QoS constraints are imposed to meet certain given probabilities of un-coded error (or, equivalently, to meet certain signal-to-noise ratio constraints), these two schemes perform closely in terms of the minimum total transmit power. However, when the QoS iv constraints are used to guarantee certain given rates, the MABC-based scheme outperforms the TDBC counterpart. In the case when a direct link exists between the two transceivers, the TDBC-based approach can outperform the MABC-based method provided that the direct link is strong enough. / UOIT

In this dissertation, advanced numerical methods for highly forward peaked scattering deterministic calculations are devised, implemented, and assessed. Since electrons interact with the surrounding environment through Coulomb interactions, the scattering kernel is highly forward-peaked. This bears the consequence that, with standard preconditioning, the standard Legendre expansion of the scattering kernel requires too many terms for the discretized equation to be solved efficiently using a deterministic method. The Diffusion Synthetic Acceleration (DSA), usually used to speed up the calculation when the scattering is weakly anisotropic, is inefficient for electron transport. This led Morel and Manteuffel to develop a one-dimensional angular multigrid (ANMG) which has proved to be very effective when the scattering is highly anisotropic. Later, Pautz et al. generalized this scheme to multidimensional geometries, but this method had to be stabilized by a diffusive filter that degrades the overall convergence of the iterative scheme. In this dissertation, we recast the multidimensional angular multigrid method without the filter as a preconditioner for a Krylov solver. This new method is stable independently of the anisotropy of the scattering and is increasingly more effective and efficient as the anisotropy increases compared to DSA preconditioning wrapped inside a Krylov solver. At the coarsest level of ANMG, a DSA step is needed. In this research, we use the Modified Interior Penalty (MIP) DSA. This DSA was shown to be always stable on triangular cells with isotropic scattering. Because this DSA discretization leads to symmetric definite-positive matrices, it is usually solved using a conjugate gradient preconditioned (CG) by SSOR but here, we show that algebraic multigrid methods are vastly superior than more common CG preconditioners such as SSOR. Another important part of this dissertation is dedicated to transport equation and diffusion solves on arbitrary polygonal meshes. The advantages of polygonal cells are that the number of unknowns needed to mesh a domain can be decreased and that adaptive mesh refinement implementation is simplified: rather than handling hanging nodes, the adapted computational mesh includes different types of polygons. Numerical examples are presented for arbitrary quadrilateral and polygonal grids.

This research addresses sizing and dimensioning of a forward-reserve warehouse, a strategic design problem that has important implications on warehouse life cycle costs including construction, inventory holding and replenishment, and material handling. Large mixed integer nonlinear models are developed that capture the complex tradeoffs among the different costs in order to achieve a global optimal design satisfying throughput requirements. We first consider the situation where the forward area includes all SKUs so that order picking is performed only in the forward area. In this case, the problem can be decomposed. The resulting sub-problem is convex and can be solved very efficiently based on the Karush-Kuhn-Tucker (KKT) conditions. This property enables the use of a Generalized Benders Decomposition (GBD) method to solve the sizing and dimensioning problem exactly. We then extend the problem to more general situations where the forward area contains a subset of SKUs. This requires integrating the sizing and dimensioning decisions with the decision to assign SKUs to the forward area based on their flow characteristics (i.e., the forward reserve allocation). A similar decomposition strategy can be employed, but the sub-problem (incorporating the forward reserve allocation) is no longer convex. A bi-level hierarchical heuristic approach is proposed that integrates a pattern search method for the master problem and optimal and heuristic algorithms for the sub-problems. Numerical results demonstrate that the proposed solution methods can efficiently find optimal or near optimal solutions for the sizing and dimensioning problem, and the resulting solutions are robust with regards to possible forecasting errors in design parameters.

In this thesis, we consider the problem of distributed detection problem in cooperative communication networks when the channel state information (CSI) is unknown. The amplify-and-forward relay strategy is considered in this thesis. Since the CSI is assumed to be unknown to the system, the joint detection and estimation approach is considered in this work. The proposed scheme in this work differs from existing joint detection and estimation schemes in that it utilizes a distributed approach, which exploits node cooperation and achieves a better system performance in cooperative communication networks. Moreover, by contrast to the existing channel estimation and symbol detection schemes, the proposed scheme is mainly developed based on the assumption that the data communication from the source to each relay node is to undergo a correlated fading channel. We derive the joint detection and estimation rules for our problem using the expectation-maximum (EM) algorithm. Simulation results show that the proposed scheme can perform well. Moreover, the obtained results show that the proposed iteration algorithm converges very fast, which implies the proposed scheme can work well in real-time applications.

In wireless communication, multipath fading distorts the phase and the amplitude of received signals and increases error rate, which degrades causes communication quality. Multiple-input-multiple-output (MIMO) techniques can be adopted to achieve diversity gain and reduce error rate. However, MIMO is hard to be implemented in mobile devices due to size limitation. With this regard, cooperative communications are proposed to allow users to cooperate each other¡¦s and then achieve diversity without equipping multiple antennas. On the other hand, if source and relays adopt fixed-rate transmission under time-varying wireless channels, it requires timely feedback about channel-information for transmitters to adjust the rate of channel encoder. To reduce overhead required for aforementioned scheme, we adopt rateless fountain codes in cooperative networks. In recent year, most related studies focus on information-theoretical aspect, but it lacks discussion of practical coding. In our work, we use fountain codes in dual-hop cooperative communication and analyse transmission rate in terms of transmitting time. Fountain code was first proposed as Luby transform codes(LTC) for erasure channels. We combine low-density parity-check code( LDPC code) and LTC in cooperative communication networks, and analyze required transmission time under different cooperative protocols.

This research investigated the need, design, and evaluation of a product capable of providing support to forward-leaning postures. Due to the high occurrence of low-back pain in industry potentially due to workers performing their tasks while assuming forward-leaning postures, along with the biological plausibility of these postures causing low-back pain, the need was established for a product that provides forward-leaning support. An envelope was quantified, ranging from the 5th percentile female to the 95th percentile male, to establish the range of potential forward-leaning postures. The design of a Support-Arm for use with current ergonomic chairs was discussed and design feature specifications were then provided. A Latin Square statistical design was employed to evaluate a Support-Arm model alongside 8 other commonly used chairs over 3 different postures. Subjects, overall, had lower peak pressures for the buttock-thigh region, increased productivity, higher comfort levels, and higher buttock-thigh contact areas when seated in the Support-Arm model chair as compared to the other chairs. Subjects, overall, also ranked this chair first over the other chairs for preferred use after having sitting experience in all 9 chairs. In an additional part of the evaluation, subjects chose their own set-up of the Support-Arm model chair. Eleven of the 18 subjects chose to use the Support-Arm when their workstation was located 36” above the floor. Subjects confirmed the need to design a Support-Arm capable of providing forward leaning support to the entire envelope of forward-leaning postures. Statistical evaluation revealed several significant differences between the chairs. The results gave no indication that the use of a Support-Arm for forward-leaning support may cause detrimental effects to users or overall chair ergonomics. Future research could track workers’ use of a Support-Arm in industry and compare their occurrence of low-back pain to a control group.

While lean manufacturing has greatly improved the efficiency of production operations, it has left US enterprises in an increasingly risky environment. Causes of manufacturing disruptions continue to multiply, and today, seemingly minor disruptions can cause cascading sequences of capacity losses. Historically, enterprises have lacked viable tools for addressing operational volatility. As a result, each year US companies forfeit billions of dollars to unpredictable capacity disruptions and insurance premiums. In this dissertation we develop a number of stochastic models that capture the dynamics of capacity disruptions in complex multi-tier flow-matching feed-forward networks (FFN). In particular, we relax basic structural assumptions of FFN, introduce random propagation times, study the impact of inventory buffers on propagation times, and make initial efforts to model random network topology. These stochastic models are central to future methodologies supporting strategic risk management and enterprise network design.

This thesis studies the subcarrier power allocation for the relayed signal in Orthogonal Frequency-Division Multiplexing (OFDM) based dual-hop system where the relay node operated in amplify-and-forward (AF) scheme. The investigated system assumes that each subcarrier at the source node transmits the signal with uniform power distribution. Considering the separated sum power constraints which the power constraint at source and relay node are uncorrelated, the conventional iterative water-filling algorithm can maximize the system capacity. However, it requires high computational complexity and the performance improvement is limited when the source node transmits the signal with uniform power distribution, subcarrier power allocation at relay node for capacity maximization is impractical. To further enhance the system performance, a novel subcarrier power allocation method is derived into a closed-form for the relayed signal to minimize the summation of equivalent noise power of the destination node. Comparing with the existing schemes, simulation results demonstrate that the proposed power scaling scheme significantly improves system average bit error rate (ABER).