Submitted by Luanna Matias (lua_matias@yahoo.com.br) on 2015-02-06T19:23:12Z No. of bitstreams: 2 Dissertação - Marcos Antônio Almeida de Oliveira - 2014..pdf: 1092566 bytes, checksum: 55edbdaf5b3ac84fe3f6835682fe2a13 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-02-19T14:34:20Z (GMT) No. of bitstreams: 2 Dissertação - Marcos Antônio Almeida de Oliveira - 2014..pdf: 1092566 bytes, checksum: 55edbdaf5b3ac84fe3f6835682fe2a13 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-02-19T14:34:20Z (GMT). No. of bitstreams: 2 Dissertação - Marcos Antônio Almeida de Oliveira - 2014..pdf: 1092566 bytes, checksum: 55edbdaf5b3ac84fe3f6835682fe2a13 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-09-03 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / A variation of the Beasley (1992) algorithm for the Euclidean Steiner tree problem is presented. This variation uses the Node-Depth-Degree Encoding, which requires an average time of O(n) in operations to generate and manipulate spanning forests. For spanning tree problems, this representation has linear time complexity when applied to network design problems with evolutionary algorithms. Computational results are given for test cases involving instances up to 500 vertices. These results demonstrate the use of the Node-Depth-Degree in an exact heuristic, and this suggests the possibility of using this representation in other techniques besides evolutionary algorithms. An empirical comparative and complexity analysis between the proposed algorithm and a conventional representation indicates the efficiency advantages of the solution found. / É apresentada uma variação do algoritmo de Beasley (1992) para o Problema árvore de Steiner Euclidiano. Essa variação utiliza a Representação Nó-Profundidade-Grau que requer, em média, tempo O(n) em operações para gerar e manipular florestas geradoras. Para problemas de árvore geradora essa representação possui complexidade de tempo linear sendo aplicada em problemas de projeto de redes com algoritmos evolutivos. Resultados computacionais são dados para casos de teste envolvendo instâncias de até 500 vértices. Esses resultados demonstram a utilização da representação Nó-Profundidade-Grau em uma heurística exata, e isso sugere a possibilidade de utilização dessa representação em outras técnicas além de algoritmos evolutivos. Um comparativo empírico e da análise de complexidade entre o algoritmo proposto e uma representação convencional indica vantagens na eficiência da solução encontrada.

We design and analyze algorithms for the following two robot navigation problems: 1. TARGET SEARCH. Given a robot located at a point s in the plane, how will a robot navigate to a goal t in the presence of unknown obstacles ? 2. LOCALIZATION. A robot is "lost" in an environment with a map of its surroundings. How will it find its true location by traveling the minimum distance ? Since efficient algorithms for these two problems will make a robot completely autonomous, they have held the interest of both robotics and computer science communities. Previous work has focussed mainly on designing competitive algorithms where the robot's performance is compared to that of an omniscient adversary. For example, a competitive algorithm for target search will compare the distance traveled by the robot with the shortest path from s to t. We analyze these problems from the worst-case perspective, which, in our view, is a more appropriate measure. Our results are : 1. For target search, we analyze an algorithm called Dynamic A*. The robot continuously moves to the goal on the shortest path which it recomputes on the discovery of obstacles. A variant of this algorithm has been employed in Mars Rover prototypes. We show that D* takes O(n log n) time on planar graphs and also show a comparable bound on arbitrary graphs. Thus, our results show that D* combines the optimistic possibility of reaching the goal very soon while competing with depth-first search within a logarithmic factor. 2. For the localization problem, worst-case analysis compares the performance of the robot with the optimal decision tree over the set of possible locations. No approximation algorithm has been known. We give a polylogarithmic approximation algorithm and also show a near-tight lower bound for the grid graphs commonly used in practice. The key idea is to plan travel on a "majority-rule map" which eliminates uncertainty and permits a link to the half-Group Steiner problem. We also extend the problem to polygonal maps by discretizing the domain using novel geometric techniques.

The popularity of the great variety of Internet usage brings about a significant growth of the data traffic in telecommunication network. Data transmission efficiency will be challenged under the premise of current network capacity and data flow control mechanisms. In addition to increasing financial investment to expand the network capacity, improving the existing techniques are more rational and economical. Various cutting-edge researches to cope with future network requirement have emerged, and one of them is called network coding. As a natural extension in coding theory, it allows mixing different network flows on the intermediate nodes, which changes the way of avoiding collisions of data flows. It has been applied to achieve better throughput and reliability, security, and robustness in various network environments and applications. This dissertation focuses on the use of network coding for multicast in fixed mesh networks and distributed storage systems. We first model various multicast routing strategies within an optimization framework, including tree-based multicast and network coding; we solve the models with efficient algorithms, and compare the coding advantage, in terms of throughput gain in medium size randomly generated graphs. Based on the numerical analysis obtained from previous experiments, we propose a revised multicast routing framework, called strategic network coding, which combines standard multicast forwarding and network coding features in order to obtain the most benefit from network coding at lowest cost where such costs depend both on the number of nodes performing coding and the volume of traffic that is coded. Finally, we investigate a revised transportation problem which is capable of calculating a static routing scheme between servers and clients in distributed storage systems where we apply coding to support the storage of contents. We extend the application to a general optimization problem, named transportation problem with degree constraints, which can be widely used in different industrial fields, including telecommunication, but has not been studied very often. For this problem, we derive some preliminary theoretical results and propose a reasonable Lagrangian decomposition approach

Dans les réseaux de télécommunications, la demande croissante pour de nouveaux services, comme la diffusion de vidéos en continu ou les conférences en ligne, engendre un besoin pour des dispositifs de télécommunication où le même contenu est acheminé depuis un émetteur unique vers un groupe de récepteurs. Cette évolution ouvre la voie au développement de nouvelles techniques d'acheminement des données, comme le multicast qui laisse un nœud du réseau copier ses données d'entrée puis retransmettre ces copies, ou le codage réseau, qui est une technique permettant à un nœud d'effectuer des opérations de codage à partir de ses données d'entrée. Cette thèse traite de la mise en place de techniques de codage au sein d'un réseau multicast filaire. Nous formalisons certains problèmes qui apparaissent naturellement dans ce contexte grâce à la recherche opérationnelle et à des outils d'optimisation mathématique. Notre objectif est de développer des modèles et des algorithmes afin de calculer, au moins de manière approchée, certaines grandeurs qui ont vocation à être pertinentes dans le cadre de la comparaison de techniques d'acheminement de données dans un réseau de télécommunications. Nous évaluons ainsi, d'un point de vue à la fois théorique et expérimental, l'impact induit par l'introduction de techniques de codage au sein d'un réseau multicast. Nous nous concentrons en particulier sur des critères importants pour un opérateur de télécommunication, comme la maximisation du débit d'information entre une source et un ensemble de destinataires dans le réseau, la minimisation de la congestion sous contrainte de demande, ou la minimisation de la perte de débit ou du coût induit par l'acheminement des données dans un réseau soumis à des pannes. / In telecommunication networks, the increasing demand for new services, like video-streaming or teleconferencing, along with the now common situation where the same content is simultaneously requested by a huge number of users, stress the need for point to many data transmission protocols where one sender wishes to transmit the same data to a set of receivers. This evolution leads to the development of new routing techniques like multicast, where any node of the network can copy its received data and then send these copies, or network coding, which is a technique allowing any node to perform coding operations on its data. This thesis deals with the implementation of coding techniques in a wired multicast network. We formalize some problems naturally arising in this setting by using operations research and mathematical optimization tools. Our objective is to develop models and algorithms which could compute, at least approximately, some quantities whose purpose is to be relevant as far as forwarding data using either multicast and network coding in telecommunications networks is concerned. We hence evaluate, both in theory and numerically, the impact of introducing coding techniques in a multicast network. We specifically investigate relevant criteria, with respect to the field of telecommunications, like the maximum amount of information one can expect to convey from a source to a set of receivers through the network, the minimum congestion one can guarantee while satisfying a given demand, or the minimum loss in throughput or cost induced by a survivable routing in a network prone to failures.

[pt] Usuários atualmente esperam consultar dados de maneira semelhante ao Google, digitando alguns termos, chamados palavras-chave, e deixando para o sistema recuperar os dados que melhor correspondem ao conjunto de palavras-chave. O cenário é bem diferente em sistemas de gerenciamento de banco de dados em que os usuários precisam conhecer linguagens de consulta sofisticadas para recuperar dados, ou em aplicações de banco de dados em que as interfaces de usuário são projetadas como inúmeras caixas que o usuário deve preencher com seus parâmetros de pesquisa. Esta tese descreve um algoritmo e um framework projetados para processar consultas baseadas em palavras-chave para bases de dados com esquema, especificamente bancos relacionais e bases de dados em RDF. O algoritmo primeiro converte uma consulta baseada em palavras-chave em uma consulta abstrata e, em seguida, compila a consulta abstrata em uma consulta SPARQL ou SQL, de modo que cada resultado da consulta SPARQL (resp. SQL) seja uma resposta para a consulta baseada em palavras-chave. O algoritmo explora o esquema para evitar a intervenção do usuário durante o processo de busca e oferece um mecanismo de feedback para gerar novas respostas. A tese termina com experimentos nas bases de dados Mondial, IMDb e Musicbrainz. O algoritmo proposto obtém resultados satisfatórios para os benchmarks. Como parte dos experimentos, a tese também compara os resultados e o desempenho obtidos com bases de dados em RDF e bancos de dados relacionais. / [en] Users currently expect to query data in a Google-like style, by simply typing some terms, called keywords, and leaving it to the system to retrieve the data that best match the set of keywords. The scenario is quite different in database management systems, where users need to know sophisticated query languages to retrieve data, and in database applications, where the user interfaces are designed as a stack of pages with numerous boxes that the user must fill with his search parameters. This thesis describes an algorithm and a framework designed to support keywordbased queries for datasets with schema, specifically RDF datasets and relational databases. The algorithm first translates a keyword-based query into an abstract query, and then compiles the abstract query into a SPARQL or a SQL query such that each result of the SPARQL (resp. SQL) query is an answer for the keywordbased query. It explores the schema to avoid user intervention during the translation process and offers a feedback mechanism to generate new answers. The thesis concludes with experiments over the Mondial, IMDb, and Musicbrainz databases. The proposed translation algorithm achieves satisfactory results and good performance for the benchmarks. The experiments also compare the RDF and the relational alternatives.

[pt] Esta tese generaliza a variante multi-período do clássico problema da Árvore de Steiner com coleta de prêmios (PCST), que visa encontrar um subgrafo conexo que maximize os prêmios recuperados de nós conectados menos o custo de utilização das arestas conectadas. Este trabalho adicionalmente: (a) permite que vértices sejam conectados à árvore em diferentes períodos de tempo; (b) impõe um orçamento pré-definido em arestas selecionadas em um horizonte específico de períodos de tempo; e (c) limita o comprimento total de arestas que podem ser adicionadas em um período de tempo. Um algoritmo branch-and-cut é fornecido para este problema, avaliando satisfatoriamente instâncias benchmark da literatura, adaptadas para uma configuração multi-período, de até aproximadamente 2000 vértices e 200 terminais em tempo razoável. / [en] This thesis generalizes the multi-period variant of the classical Prizecollecting Steiner Tree Problem, which aims at finding a connected subgraph that maximizes the revenues collected from connected nodes minus the costs to utilize the connecting edges. This work additionally: (a) allows vertices to be added to the tree at different time periods; (b) imposes a predefined budget on edges selected over a specific horizon of time periods; and (c) limits the total length of edges that can be added over a time period. A branch-and-cut algorithm is provided for this problem, satisfactorily evaluating benchmark instances from the literature, adapted to a multi-period setting, up to approximately 2000 vertices and 200 terminals in reasonable time.

無線網狀網路(WMNs)為目前熱門的廣域無線網路接取技術。使用者可以透過WMNs隨時在各處使用即時影音播放的服務。相較於傳統的主從式架構，低成本且容易建置的點對點架構更適用於影音串流的應用；在進行即時影音播放的時候，影音播放的品質便為相當重要的目標。因為多媒體應用服務對於延遲及網路傳輸效能相當敏感，且WMNs的傳輸過程中常會面臨同頻道干擾的問題而使得傳輸的效能銳減，當每個網路節點都具有多張無線網路卡時，如何善用WMNs多頻道傳輸的特性提升效能更是顯得特別重要。在本篇論文中，我們利用WMNs多頻道傳輸的特性進行多媒體群播傳輸，參考史坦納樹的概念來改善現有的MAODV路由演算法，以傳輸品質較佳的鏈結改良原本尋找最小跳躍數路徑的方式，建立兩棵完全互斥的群播樹作為點對點傳輸的骨幹網路，並以MDC的概念將影像串流編碼成兩份獨立的子串流分別經由不同的群播樹傳輸。經實驗評估，我們的方法在網路負載較高的環境下能有效的降低延遲並提高整體系統的效能。 / In WMNs, users can enjoy the real-time video streaming service anytime and anywhere through the services. Compared to the client/server model, P2P approaches is more suitable for video streaming applications because of its low cost and easy deployment. But when using the real-time multimedia service in WMNs, the multimedia applications are very sensitive to delay time and the performance of packets transmission. And the performance is significantly influenced by the co-channel interference, so that it is important to know how to transmit by multi-channel to enhance the performance. In our approach, we choose the better quality links for routing instead of the minimum hop-count path in MAODV. Then we distribute the video streaming to receivers by multicast in multi-channel WMNs, and refer to the Steiner tree concept to modify the MAODV routing protocol to construct two disjoint multicast trees as the backbone for the P2P structure. Therefore, we can adopt the MDC scheme to encode the video into two independent sub-streams and transmit separately along these trees. Experiment results show that in higher network traffic load environment, our scheme is more effective to reduce the latency and improve overall system performance.

The multi-net Global Routing Problem (GRP) in VLSI physical design is a problem of routing a set of nets subject to limited resources and delay constraints. Various state-of-the-art routers are available but their main focus is to optimize the wire length and minimize the over ow. However optimizing wire length do not necessarily meet timing constraints at the sink nodes. Also, in modern nano-meter scale VLSI process the consideration of process variations is a necessity for ensuring reasonable yield at the fab. In this work, we try to nd a fundamental strategy to address the timing-driven Steiner tree construction (i.e., the routing) problem subject to congestion constraints and process variation. For congestion mitigation, a gradient based concurrent approach (over all nets) of Erzin et. al., rather than the traditional (sequential) rip-and-reroute is adopted in or- der to propagate the timing/delay-driven property of the Steiner tree candidates. The existing sequential rip-up and reroute methods meet the over ow constraint locally but cannot propagate the timing constraint which is non-local in nature. We build on this approach to accommodate the variation-aware statistical delay/timing requirements. To further reduce the congestion, the cost function of the tree generation method is updated by adding history based congestion penalty to the base cost (delay). Iterative use of the timing-driven Steiner tree construction method and history based tree construction procedure generate a diverse pool of candidate Steiner trees for each net. The gradient algorithm picks one tree for each net from the pool of trees such that congestion is e ciently controlled. As the technology scales down, process variation makes process dependent param- eters like resistance, capacitance etc non-deterministic. As a result, Statistical Static Timing Analysis or SSTA has replaced the traditional static timing in nano-meter scale VLSI processes. However, this poses a challenge regarding the max/min-plus algebra of Dijkstra like approximation algorithm that builds the Steiner trees. A new approach based on distance between distributions for nding maximum/minimum at the nodes is presented in this thesis. Under this metric, the approximation algorithm for variation aware timing driven congestion constrained routing is shown to be provably tight and one order of magnitude faster than existing approaches (which are not tight) such as the MVERT. The results (mean value) of our variation aware router are quite close to the mean of the several thousand Monte Carlo simulations of the deterministic router, i.e the results converge in mean. Therefore, instead of running so many deterministic Monte Carlo simulations, we can generate an average design with a probability distribution reasonably close to that of the actual behaviour of the design by running the proposed statistical router only once and at a small fraction of the computational e ort involved in physical design in the nano regime VLSI. The above approximation algorithm is extended to local routing, especially non- Manhattan lambda routing which is increasingly being allowed by the recent VLSI tech- nology nodes. Here also, we can meet delay driven constraints better and keep related wire lengths reasonable.

Classical planning is the problem of nding a sequence of actions that take an agent from an initial state to a desired goal situation, assuming deter- ministic outcomes for actions and perfect information. Satis cing planning seeks to quickly nd low-cost solutions with no guarantees of optimality. The most e ective approach for satis cing planning has proved to be heuristic search using non-admissible heuristics. In this thesis, we introduce several such heuristics that are able to take into account costs on actions, and there- fore try to minimize the more general metric of cost, rather than length, of plans, and investigate their properties and performance. In addition, we show how the problem of planning with soft goals can be compiled into a classical planning problem with costs, a setting in which cost-sensitive heuristics such as those presented here are essential. / La plani caci on cl asica es el problema que consiste en hallar una secuencia de acciones que lleven a un agente desde un estado inicial a un objetivo, asum- iendo resultados determin sticos e informaci on completa. La plani caci on \satis cing" busca encontrar una soluci on de bajo coste, sin garant as de op- timalidad. La b usqueda heur stica guiada por heur sticas no admisibles es el enfoque que ha tenido mas exito. Esta tesis presenta varias heur sticas de ese g enero que consideran costes en las acciones, y por lo tanto encuentran soluciones que minimizan el coste, en lugar de la longitud del plan. Adem as, demostramos que el problema de plani caci on con \soft goals", u objetivos opcionales, se puede reducir a un problema de plani caci on clasica con costes en las acciones, escenario en el que heur sticas sensibles a costes, tal como las aqu presentadas, son esenciales.