京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24744号 / 情博第832号 / 新制||情||139(附属図書館) / 京都大学大学院情報学研究科システム科学専攻 / (主査)准教授 深沢 圭一郎, 教授 田中 利幸, 教授 石井 信 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Les réseaux de capteurs sans fils sont composés de noeuds capteurs capables de mesurer certains paramètres de l’environnement, traiter l’information recueillie, et communiquer par radio sans aucune autre infrastructure. La communication avec les autres noeuds consomme le plus d’énergie. Les protocoles de collecte des données des réseaux de capteurs sans fils doit donc avoir comme premier objectif de minimiser les communications. Une technique souvent utilisée pour ce faire est l’agrégation des données. Les réseaux de capteurs sans fils sont souvent déployés dans des environnements ouverts, et sont donc vulnérables aux attaques de sécurité. Cette thèse est une contribution à la conception de protocoles sécurisés pour réseaux de capteurs sans fils. Nous faisons une classification des principaux protocoles d’agrégation de données ayant des propriétés de sécurité. Nous proposons un nouveau protocole d’agrégation (ESPPA). ESPPA est basé sur la construction d’un arbre recouvrant sûr et utilise une technique de brouillage pour assurer la confidentialité et le respect de la vie privée. Notre algorithme de construction (et re-construction) de l’arbre recouvrant sûr tient compte des éventuelles pannes des noeuds capteurs. Les résultats de nos simulations montrent que ESPPA assure la sécurité en terme de confidentialité et de respect de la vie privée, et génère moins de communications que SMART. Finalement, nous proposons une extension du schéma de construction de l’arbre recouvrant sûr qui identifie les noeuds redondants en terme de couverture de captage et les met en veille. Les résultats de nos simulations montrent l’efficacité de l’extension proposée. / WSNs are formed by sensor nodes that have the ability to sense the environment, process the sensed information, and communicate via radio without any additional prior backbone infrastructure. In WSNs, communication with other nodes is the most energy consuming task. Hence, the primary objective in designing protocols for WSNs is to minimize communication overhead. This is often achieved using in-network data aggregation. As WSNs are often deployed in open environments, they are vulnerable to security attacks. This thesis contributes toward the design of energy efficient secure and privacy preserving data aggregation protocol for WSNs. First, we classify the main existing secure and privacy-preserving data aggregation protocols for WSNs in the literature. We then propose an energy-efficient secure and privacy-preserving data aggregation (ESPPA) scheme for WSNs. ESPPA scheme is tree-based and achieves confidentiality and privacy based on shuffling technique. We propose a secure tree construction (ST) and tree-reconstruction scheme. Simulation results show that ESPPA scheme effectively preserve privacy, confidentiality, and has less communication overhead than SMART. Finally we propose an extension of ST scheme, called secure coverage tree (SCT) construction scheme. SCT applies sleep scheduling. Through simulations, we show the efficacy and efficiency of the SCT scheme. Beside the work on secure and privacy preserving data aggregation, during my research period, we have also worked on another interesting topic (i.e., composite event detection for WSNs). Appendix B presents a complementary work on composite event detection for WSNs.

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.

This thesis deals with ray tracing methods and their acceleration. It gives partial study and review of algorithms from classical ray shooting algorithm to recursive approach up to distributed ray tracing algorithm. Significant part of this thesis is devoted to BSP tree structure and its subclass of k-D tree, it shows simple algorithm for its construction and traversal. The rest of thesis is dealing with k-D tree construction techniques, which are based on the right choice of the splitting plane inside the every cell of k-D tree. The techniques upon the thesis is based on are space median, object median and relatively new cost model technique named SAH, otherwise as surface area heuristic. All three techniques are put into testing and performance comparison. In the conclusion the results of tests are reviewed, from where SAH is coming out as a winner.