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We consider a hierarchical spectrum sharing network consisting of a primary and a cognitive secondary transmitter-receiver pair, with non-backlogged traffic. The secondary transmitter may utilize cooperative transmission techniques to relay primary traffic while superimposing its own information, or transmit opportunistically when the primary user is idle. The secondary user meets a dilemma in this scenario. Choosing cooperation it can transmit a packet immediately even if the primary queue is not empty, but it has to bear the additional cost of relaying, since the primary performance needs to be guaranteed. To solve this dilemma we propose dynamic cooperative secondary access control that takes the state of the spectrum sharing network into account. We formulate the problem as a Markov Decision Process (MDP) and prove the existence of a stationary policy that is average cost optimal. Then we consider the scenario when the traffic and link statistics are not known at the secondary user, and propose to find the optimal transmission strategy using reinforcement learning. With extensive numerical evaluation, we demonstrate that dynamic cooperation with state aware sequential decision is very efficient in spectrum sharing systems with stochastic traffic, and show that dynamic cooperation is necessary for the secondary system to be able to adapt to changing load conditions or to changing available energy resource. Our results show, that learning based access control, with or without known primary buffer state, has close to optimal performance. / <p>QS 2013</p>

Call centers have been introduced with great success by many service‐oriented companies. They become the main point of contact with the customer, and an integral part of the majority of corporations. The large‐scale emergence of call centers has created a fertile source of management issues. In this PhD thesis, we focus on various operations management issues of multi‐skill and multichannel call centers. The objective of our work is to derive, both qualitative and quantitative, results for practical management. In the first part, we focus on architectures with limited flexibility for multi‐skill call centers. The context is that of call centers with asymmetric parameters: unbalanced workload, different service requirements, a predominant customer type, unbalanced abandonments and high costs of crosstraining. The most knowing architectures with limited flexibility such as chaining fail against such asymmetry. We propose a new architecture referred to as single pooling with only two skills per agent and we demonstrate its efficiency under various situations of asymmetry. In the second part, we focus on routing problems in multi‐channel call centers. In the first study, we consider a blended call center with calls arriving over time and an infinitely backlogged queue of emails. The call service is characterized by three successive stages where the second one is a break. We focus on the optimization of the email routing to agents. The objective is to maximize the throughput of emails subject to a constraint on the call waiting time. Various guidelines to call center managers are provided. In particular, we prove for the optimal routing that all the time at least one of the two email routing parameters has an extreme value. In the second study, we examine a threshold policy on the reservation of agents for the inbound calls. We study a general non‐stationary model where the call arrival follows a non‐homogeneous Poisson process. The optimization problem consists on maximizing the throughput of outbound tasks under a constraint on the waiting time of inbound calls. We propose an efficient adaptive threshold policy easy to implement. This scheduling policy is evaluated through a comparison with the optimal performance measures found in the case of a constant stationary arrival rate, and also a comparison with other intuitive adaptive threshold policies in the general non‐stationary case. In the third study, we consider a call center model with a call back option, which allows to transform an inbound call into an outbound one. The optimization problem consists on minimizing the expected waiting time of the outbound calls while respecting a service level constraint on the inbound ones. We propose a routing policy with two thresholds, one on the reservation of the agents for inbound calls, and another on the number of waiting outbound calls. A curve relating the two thresholds is determined.

Les centres d’appels connaissent un grand succès depuis leur introduction dans les entreprises de service. Ils sont le principal point de contact avec les clients, et une composante essentielle de la majorité des entreprises. L’émergence des centres d’appels à grande échelle a suscité de nombreuses problématiques de management. Dans cette thèse, nous considérons des problématiques de management orientées sur les centres multi‐canaux et multi‐compétences. L’objectif de notre travail est de trouver des résultats qualitatifs et quantitatifs utiles pour le management. Dans la première partie, nous considérons les architectures de centres multi‐compétences à flexibilité limitée. Le contexte est celui de centres d’appels avec des paramètres asymétriques : charge de travail non équilibrée, différents temps de services, prédominance d’une catégorie de clients, taux d’abandons variables et couts élevés de la multi‐compétence. Les architectures les plus connues avec flexibilité limitée comme chaining ne résistent pas à de telles asymétries. Nous proposons une nouvelle architecture, appelée Single Pooling avec seulement deux compétences par agent et nous démontrons son efficience dans diverses situations d’asymétrie. Dans la seconde partie, nous nous intéressons aux problèmes de routage dans les centres d’appels multi‐canaux. Dans le premier projet, nous considérons un centre avec des appels arrivant au fil du temps et des emails présents en nombre illimité. Le service des appels se fait en trois étapes dont la seconde est une pause pour l’agent. Nous cherchons à optimiser le routage des emails. L’objectif est de maximiser le débit d’emails traités sous contrainte de temps d’attente pour les appels. De nombreuses recommandations sont proposées au manager. En particulier, nous démontrons que pour obtenir un routage optimal il est nécessaire de fixer à une valeur extrême au moins l’un des deux paramètres définissant le routage des emails. Dans le second projet, nous étudions une politique de seuil de réservation d’agents pour les appels en réception. Nous considérons un cas général de modèle non stationnaire ou le processus d’arrivée des appels est Poisson non homogène. Le problème d’optimisation est la maximisation du débit de taches en émission sous contrainte de qualité de service sur les appels en réception. Nous proposons une méthode efficiente et facile à implémenter de changement adaptatif de seuil. Cette politique est évaluée en comparaison avec les performances optimales trouvées dans le cas particulier de taux d’arrivée constant, et en comparaison avec d’autres méthodes intuitives de changement adaptatif de seuil dans le cas général non stationnaire. Dans le troisième projet, nous considérons un modèle de centre avec option de rappels. Cette option permet de transformer un appel en réception en un appel en attente d’émission. Le problème d’optimisation est la minimisation du temps d’attente des appels en émission sous contrainte de qualité de service pour les appels en réception. Nous proposons une politique de routage à deux seuils, un sur la réservation d’agents pour les appels en réception et un sur le nombre d’appels en attente d’émission. Nous déterminons une courbe optimale entre ces deux seuils / Call centers have been introduced with great success by many service‐oriented companies. They become the main point of contact with the customer, and an integral part of the majority of corporations. The large‐scale emergence of call centers has created a fertile source of management issues. In this PhD thesis, we focus on various operations management issues of multi‐skill and multichannel call centers. The objective of our work is to derive, both qualitative and quantitative, results for practical management. In the first part, we focus on architectures with limited flexibility for multi‐skill call centers. The context is that of call centers with asymmetric parameters: unbalanced workload, different service requirements, a predominant customer type, unbalanced abandonments and high costs of crosstraining. The most knowing architectures with limited flexibility such as chaining fail against such asymmetry. We propose a new architecture referred to as single pooling with only two skills per agent and we demonstrate its efficiency under various situations of asymmetry. In the second part, we focus on routing problems in multi‐channel call centers. In the first study, we consider a blended call center with calls arriving over time and an infinitely backlogged queue of emails. The call service is characterized by three successive stages where the second one is a break. We focus on the optimization of the email routing to agents. The objective is to maximize the throughput of emails subject to a constraint on the call waiting time. Various guidelines to call center managers are provided. In particular, we prove for the optimal routing that all the time at least one of the two email routing parameters has an extreme value. In the second study, we examine a threshold policy on the reservation of agents for the inbound calls. We study a general non‐stationary model where the call arrival follows a non‐homogeneous Poisson process. The optimization problem consists on maximizing the throughput of outbound tasks under a constraint on the waiting time of inbound calls. We propose an efficient adaptive threshold policy easy to implement. This scheduling policy is evaluated through a comparison with the optimal performance measures found in the case of a constant stationary arrival rate, and also a comparison with other intuitive adaptive threshold policies in the general non‐stationary case. In the third study, we consider a call center model with a call back option, which allows to transform an inbound call into an outbound one. The optimization problem consists on minimizing the expected waiting time of the outbound calls while respecting a service level constraint on the inbound ones. We propose a routing policy with two thresholds, one on the reservation of the agents for inbound calls, and another on the number of waiting outbound calls. A curve relating the two thresholds is determined.

Un Service d’urgence (SU) est le service hospitalier ayant comme responsabilité de fournir des soins non programmés à une grande variété de patients, 24 heures sur 24, 7 jours sur 7. Les SU sont actuellement confrontés à un problème international et récurrent, à savoir la saturation des urgences qui résulte de l’actuelle inadéquation entre les capacités médicales et la demande des patients. L'objectif est de développer des solutions internes et économiques permettant d’atténuer le phénomène de saturation des urgences et d’améliorer leur performance, à l'aide de méthodes issues de la Recherche Opérationnelle/Gestion des Opérations (RO/GO). Ces solutions sont d'un grand intérêt pour les gestionnaires. Afin d'atteindre cet objectif, nous abordons trois ensembles de questions de recherche.La première catégorie comprend des questions prospectives portant sur les indicateurs clés de performance (ICP) ainsi que sur les différents facteurs contribuant à l’encombrement des urgences. La deuxième catégorie est constituée de questions liées au dimensionnement de la capacité des ressources humaines dans un SU. Un modèle réaliste de simulation à événements discrets des urgences est élaboré. En utilisant l'optimisation basée sur la simulation, la durée moyenne de séjour des patients (LOS) est minimisée, en intégrant une contrainte budgétaire ainsi qu’une contrainte assurant que les patients les plus critiques accèderont à un médecin dans un délai déterminé. Les résultats obtenus permettent de fournir aux gestionnaires des urgences des indications utiles sur l'impact du budget sur la performance et sur la manière dont les investissements devraient être priorisés et répartis entre les ressources, ainsi que sur l'effet de la prise en compte de deux principaux ICP différents. Nous proposons également une heuristique pour l'optimisation de la structure des shifts (roulements) du personnel dans la journée. La méthode combine l'optimisation basée sur la simulation avec de la programmation linéaire. La troisième catégorie de questions porte sur le processus de soins des patients. Nous analysons des modifications et des alternatives innovantes dans le parcours du patient (à budget fixe). Typiquement, dans les pratiques actuelles, chaque patient dans un SU est affecté à un seul médecin qui en sera exclusivement responsable pendant toutes les étapes du processus (règle du "Même Patient Même Médecin", MPMM). Dans un premier temps, nous menons une enquête auprès des praticiens qui confirme que MPMM représente la pratique standard dans la plupart des SU à travers le monde. L’enquête révèle également que la suppression de cette règle est très controversée parmi les urgentistes. Nous utilisons ensuite une modélisation en réseau de files d’attente Erlang-R contenant une complexité additionnelle. Nous montrons et quantifions les avantages potentiels de la suppression de la restriction MPMM en fonction des paramètres du système. Une seconde étude portant sur le processus est menée, à savoir la prescription des examens par l’infirmière chargée du tri (PIT) avant la consultation initiale. Nous comparons le fait d’autoriser l’infirmière à prescrire certains examens complémentaires, avec la procédure standard consistant à attendre que le médecin examine le patient et lui prescrive des examens. Nous démontrons l'efficacité de PIT sur la performance du SU en fonction de paramètres clés, tels que le niveau de compétence de l’infirmière, la charge du système et l'extension de la durée du tri.De manière générale, cette thèse aborde d’innovantes questions de recherche dans la gestion des opérations des SU. Elle fournit aux décideurs des recommandations et des outils permettant d’améliorer la performance des urgences. Cette thèse ouvre également la voie pour de futurs axes de recherche liés à l'optimisation des opérations dans les SU. / Emergency Department (ED) is the service within hospitals responsible for providing unscheduled care to a wide variety of patients over 24 hours a day, 7 days a week. As a result to the existing mismatch between available caring capacity and patients demand, EDs are currently facing a recurrent worldwide problem, namely overcrowding. The objective of this thesis is to develop internal and cost-effective solutions to alleviate overcrowding in EDs and improve their performance, using Operations Research/Operations Management (OR/OM) methods. Such solutions are of great interest for managers. In order to achieve this objective, we address a series of research questions.The first category of research questions include prospective questions about ED Key Performance Indicators (KPIs) and about the diverse factors contributing to overcrowding. We first conduct a detailed literature review on the commonly used KPIs from an OR/OM perspective. The review summarizes the advantages and drawbacks of each KPI and provides several useful insights. In addition, a series of statistical analysis are performed in the purpose of identifying the main influencing factors of performance.The second category consists in resource-related questions that are associated to the dimensioning of ED resource capacity. A realistic ED discrete-event simulation model is thus proposed. The model accounts for the most essential structural and functional characteristics of EDs thanks to a close collaboration with practitioners. Using simulation optimization, we minimize the patient average length of stay (LOS), by integrating a staffing budget constraint and a constraint securing that the most severe incidents will see a doctor within a specified time limit. The obtained results allow us to provide useful insights to managers about the impact of the budget on performance and how investments priorities should be allocated among resources, as well as the effect of combining two different major KPIs. Furthermore, we propose a heuristic for the optimization of the shifts of human resources. The method combines simulation optimization and linear programming.The third category of questions deals with process-related issues. We investigate potential alternative and innovative ED patient flow designs (with fixed budget). Typically in current ED practices, each patient is assigned to a single physician who will be exclusively responsible of him/her during all stages of the process (“Same Patient Same Physician”, SPSP rule). We conduct a survey which confirms that SPSP stands as the standard practice in most EDs worldwide, and that removing SPSP rule is very controversial among practitioners. We next use a complexity-augmented Erlang-R queueing network modeling. We show and quantify the potential benefits of removing the SPSP restriction as a function of the system parameters. For a second process-related issue, we compare the Triage Nurse ordering (TNO) diagnostic tests against the standard procedure, i.e., waiting for the physician to examine the patient and order tests. We demonstrate the efficiency of TNO on ED performance as a function of key parameters, such as triage nurse ability, system load and triage time extension.In summary, this thesis addresses innovative OM research questions for EDs. It provides decision makers with recommendations and tools in order to improve ED performance. It also highlights various avenues for future research related to the optimization of ED operations.

Made available in DSpace on 2016-06-02T19:05:59Z (GMT). No. of bitstreams: 1 4685.pdf: 5011854 bytes, checksum: 20592729fa201c69f10672347d91c2a5 (MD5) Previous issue date: 2012-08-31 / Financiadora de Estudos e Projetos / Managing multiple systems such as machine tools, vehicles, aircraft, among others, demand a very intense flow of data between them and the system manager. Researches have been developed in the design and implementation of scalable architectures that meet these demands leading to interesting questions of performance. The objective of this work is to propose a low cost scalable architecture for embedded applications, using pools of personal computers for high performance storage, retrieval and processing of information. It is driven by strong demand for tracking and monitoring of machines and vehicles, covering concepts of mobile networks with satellites and GPRS technology together with the requirement of reliability and performance in the sending of information. Proposes the definition of a server structure, whose distribution is transparent to the application, which is responsible for the receipt of messages from embedded devices via radio frequency technology, decoding and integration of information in the database and subsequent recovery of these information s. Through simulation of different modeled strategies using queuing theory to determine the architecture and the use of predictive mathematical methods for estimating the future burden for the server application, it was possible to obtain a solution that satisfactorily met the assumptions of the research. Thus, it is concluded that it is possible to estimate trends peaks processing information for telemetry applications fleet. / O gerenciamento remoto de múltiplos sistemas tais como máquinas operatrizes, veículos, aviões, dentre outros, demanda um fluxo bastante intenso de dados entre eles e o sistema gerenciador. Pesquisas têm sido desenvolvidas na concepção e implementação de arquiteturas escaláveis que atendam essas demandas levando a questões interessantes de desempenho. O objetivo deste trabalho é propor uma arquitetura escalável de baixo custo para aplicações embarcadas, utilizando pools de computadores pessoais para obter alto desempenho no armazenamento, recuperação e tratamento da informação. É motivado pela grande demanda de rastreamento e monitoramento de máquinas e veículos, contemplando conceitos de redes móveis com tecnologia de satélites e GPRS, juntamente com o requisito de confiabilidade e desempenho no envio da informação. Propõe a definição de uma estrutura de servidor, cuja distribuição é transparente para a aplicação, à qual compete o recebimento das mensagens dos equipamentos embarcados através de tecnologia de radio frequência, decodificação e inserção das informações num banco de dados e posterior recuperação destas informações. Através da simulação de diferentes estratégias modeladas, utilizando a teoria das filas, para determinação da arquitetura e a utilização de métodos matemáticos preditivos para estimação da carga futura para a aplicação servidora, foi possível obter uma solução que atendeu satisfatoriamente às premissas da pesquisa. Dessa forma, conclui-se que é possível estimar tendências de picos de processamento de informação para aplicações de telemetria de frotas.

No description available.

The master's thesis aims to introduce and study the issue of frequency hopping with collsion avoidance (FH/CA). On this basis, design a computer program for simulating the operation of a radio systém FHCA, who works in the band used by other systems FH/CA . This simulation programm using MATLAB software to implement verify the correctness of programs. Use simulator to obtain date about the intensity of interference systems FH/CA for the chosen scenario. This work consists of five parts: the first part consists of describing the queuing system, the second part of the description of the radio frequency system with collision avoidence FH / CA, the third part of the description of the simulation model. The fourth part includes verification of the model in the fifth and last section inspects results are shown.