This study investigates the Internet topology characterization on AS level driven from Border Gateway Protocol (BGP) tables which are collected from Réseaux IP Européens (RIPE) datasets during the seven year period, from 2003.07.30 to 2010.07.30. The investigation shows that despite of the growth of the Internet with lack of centralized control, some properties of the Internet follow certain rules and some properties remain the same during years. It demonstrates that the Internet, on AS level, exists in the form of clusters of ASs and the connected ASs with higher connectivity become even more connected during time. The spectral analysis of adjacency and normalized Laplacian matrix shows that the eigenvalues of both matrixes follow power-laws with high correlation coefficient with no considerable change in exponent values during years.

Nowadays, and with the growing interest for VoIP and its different uses through various softwares, everybody seems to agree about the fact that this family of technologies has made its place as the future of voice use in telecommunications. PSTN is in fact leaving gradually its place to this simpler technology in the few upcoming years. The main subject of this thesis will then be the domain of voice over IP. The goal of this thesis is to investigate from point to point how Skype contacts can be integrated into the existing software: “Aastra BluStar” client, and which functions can be integrated. A second goal was to implement a prototype allowing this operation, to prove its efficiency, and finally to decide if there are other functionalities that can be added further on. At the end of the thesis, an experiment of the prototype will be shown, presenting the results that were reached so far, and what can still be done to make the project even more complete.

This thesis presents an algorithm for finding the minimal interruptioncost associated with the loads.Electric power systems are necessary to transfer electric energy fromproducers to consumers. The power system may lose stability as thesenonlinear systems are subject to contingencies. The loss of stabilitymay result in large costs for the society, by the loss of productivityand worsening standard of living. If the likelihood of instability is low,then it may be that it is not economically motivated to allocate costlyresources necessary to prevent this from happening. For some casesload shedding is the alternative with best economical performance, torestore the stability and ensure that delivery of power is not interrupted.With increasing amounts of renewables in a power system, the planningand scheduling of the electric power production will get more difficultto forecast and control. Therefore the system operators will needto be able to handle more diverse situations than before. Thus thereis a need to find computationally efficient methods to predict systemstability and the minimal load shedding needed.This report uses second-order approximations to the stability boundariesof the system, developed and calculated by Magnus Perninge andCamille Hamon to determine how much and where the load sheddingshould be done to shed the minimal amount of load that restores thestability of the system.Two cases, the IEEE 9-bus system and the IEEE 39-bus system,illustrates the proposed method and compares three different methodsused to determine the load shedding. The results show that the approximationscan be used to minimize the load shedding, and that theamount of load shed is significantly reduced. Time-domain simulationsof the system were necessary to ensure the stability of the system anddetermine of much margin that is needed to the approximations.The methods and approximations used in this report could in thefuture be applied to real power systems, a possible application is tocalculate the severity of contingencies and use the information to minimizethe total costs of the system when considering operation andinvestments. Another possible application is to design automatic loadshedding controllers using wide-area monitoring to increase the systemreliability. / I detta examensarbete presenteras en algoritm för att finna de minimalaavbrottskostnaderna för lasterna i elkraftssystem.Elkraftssystem kallas de system som har till uppgift att möjliggöraöverföring av elektrisk energi från producenter till konsumenter. Dessasystem är icke-linjära och kan under vissa förhållanden bli instabilaoch göra hela eller delar av elnätet strömlöst, vilket medför stor samhälleligpåverkan i form av försämrad levnadsstandard och kostnaderför produktionsbortfall. Dock är det inte alltid ekonomiskt lönsamt attlägga betydande resurser på att förhindra att systemet blir instabilt,om sannolikheten för att detta händer är låg.Att koppla bort last vid kritiska situationer, till exempel vid fel påviktiga kraftledningar, kan därför i vissa fall vara det mest ekonomiskaalternativet för att undvika att systemet blir instabilt. En ökande andelförnybar energi i ett elkraftssystem gör produktion av elektrisk energimer svårprognosticerad och svårstyrd. Därför bör man ta hänsyn till ettbredare urval situationer än tidigare för att kunna bedöma stabilitetenhos systemet. Detta ställer krav på snabba metoder för att bedömasystemets stabilitet och beräkna vilka lastbortkopplingar som krävs.Denna rapport utnyttjar andragradsapproximationer till stabilitetsgränsernaför systemet utvecklade och beräknade av Magnus Perningeoch Camille Hamon för att kunna bestämma var och hur mycket lastsom ska kopplas bort, så att systemet återfår sin stabilitet för en såliten mängd last bortkopplad som möjligt. Genom simuleringar beräknasdärefter hur mycket marginal till stabilitetsgränserna som krävs föratt återge systemet transienta stabilitet.Två fallstudier, ett för IEEEs 9-nods system och ett för IEEEs 39-nods system, illustrerar metoden och jämför den med två andra metoder,för att undersöka metodens prestanda. Resultaten visar hur den föreslagnaalgoritmen minimerar lastbortkopplingen jämfört med de andrametoderna, och att mängden last som blir bortkopplad minskar betydligt.Simuleringar av systemet behövdes för att undersöka systemetsstabilitet och bestämma hur mycket marginal till ytorna som krävs.Metoderna och approximationerna som utnyttjades i denna rapportskulle kunna användas i verkliga elkraftssystem, en tillämpning vore attminimera kostnaderna för systemet genom att ranka hur allvarliga feli systemet är, vilket kan utnyttjas för att minimera kostnader för driftoch investeringar. En annan möjlig tillämpling är automatisk lastbortkopplingför att minimera de kostnader som uppstår om systemet blirinstabilt.

Electricity is a sector in crisis in Senegal. The main part of production and all the activities oftransmission and distribution of electricity are managed by the Senegalese National Society ofElectricity called SENELEC which is encountering enormous difficulties. One of the mostimportant problems is the fact that 21% of the produced energy is lost without being sold.This figure is enormous but quite typical with regards to African countries.Moreover, the distribution of these losses is insufficiently known. Only the production andtransmission losses can be determined from frequent and accurate measurements. Thedistribution losses represent the rest and constitute more than 80% of the losses. However, thedistribution between technical and non-technical losses (essentially due to fraud) is unknownin the distribution grid. In addition, the distribution of distribution technical losses betweenthe 30 kV, 6.6 kV and 400V grids is unknown. The goal of this Master’s Thesis is to estimatethese unknown losses. Moreover, some recommendations are suggested to reducetransmission and distribution losses.Regarding the transmission grid, Senelec does not take transmission losses into account in itsdispatching decisions, which increases transmission losses. After a Matlab modeling of thetransmission grid, a basic optimal dispatching program was developed to include losses and toprove that it would be better to consider losses in the dispatching decision.The study of the distribution grid constitutes the main part of this Master’s Thesis. Thedistribution grid can be divided in a medium-voltage grid (30 kV and 6.6 kV) and a lowvoltagegrid (400V). Losses in medium-voltage grid are estimated by the modeling of a partof this grid by using the software PSAF. Losses in low-voltage grid cannot be estimated thisway because of the lack of knowledge regarding the structure of this grid; thus, these lossesare estimated using a semi-empirical formula. Finally, non-technical distribution losses arededuced by calculating the difference between the total losses and the technical losses.The results show that the main part of the losses in Senegal are non-technical losses, whichrepresent 2/3 of the total losses and 40 billion of FCFA (61 million €), which is twice as highas what the company believed. High priority must be given to reduce them by an ambitiousplan against fraud. Technical losses even if they are smaller are not negligible and can also bereduced with some well-focused actions.

There has been a substantial interest recently in privacy preserving problems in various application domains, including data publishing, data mining, classication, secret voting, private querying of database, playing mental poker, and many others. The main constraint is that entities involved in the system are unwilling to reveal the data they hold or make them public. However, they may want to collaborate and nd the solution of a bigger computational problem without revealing the privately held data. There are several approaches for addressing such issues, including cryptographic methods, transformation methods, and parallel and distributed computation techniques. In this thesis, these three methods are highlighted and a greater emphasis is placed on the last one. In particular, we discuss the theoretical backgrounds of optimization decomposition techniques. We further point out key literature associated with the privacy preserving problems and provide basic classications of their treatments. We focus to a particular interesting application, namely the car parking problem, or parking slot assignment problem. To solve the problem in a privacy preserving manner, a new parallel and distributed computation method is proposed. The goal is to allocate the parking slots to the cars, but without revealing anyone else the intended destinations. We apply decomposition techniques together with projected subgradient method to address this problem and the result is a decentralized privacy preserving car parking algorithm. We compare our algorithm with three other methods and numerically evaluate the performance of the proposed algorithm, in terms of optimality and as well as the computational speed. Despite the reduced computational complexity of the proposed algorithm, it provides close-to-optimal performance.

Recently there has been an increasing interest in applications that enable users in the proximity of one another to share experiences, discover surrounding events, play online games and in general develop proximity based social networks. Most of the existing applications are based on cellular network communications, combined with over-the-top (OTT) solutions involving either registration at an application server and/or obtaining location information from a positioning system such as Global Positioning System (GPS). However, registration at a server often requires continuous registration updates due to, for example, mobility and changes in user population, which is a tedious and resource consuming process. In addition, using GPS drains the battery of devices. Since the spectrum used for cellular network is limited, it can become a scarce resource with increasing quantity of the devices. In order to deal with these problems, the concept of direct Device-to-Device (D2D) communication has been proposed as a solution. Using D2D technology, devices can discover nearby devices without extra positioning information. It can not only increase the spectrum efficiency, but also improve the coverage of cellular network. The discovery of devices can be prepared before the actual communication phase or proceed simultaneously. In this work, we mainly investigate the former one, which is called a-priori discovery. In fact, a-priory device discovery provides a value on its own right, independently of a subsequent communication phase using D2D or traditional cellular communication. Previous studies indicate that ad hoc D2D discovery (i.e. without cellular network assistance) is feasible but time, resource and energy consuming. Recognizing this problem, both academia and industry pay more attention to the D2D discovery in cellular spectrum, where D2D discovery can be assisted by a cellular radio access network. Despite this interest, to the best of our knowledge, there is essentially no work on identifying different degrees of network assistance (that we call the “network assistance levels”) and evaluating the potential gains of specific netw ork assistance algorithms. Therefore, in this thesis work we develop algorithms that take advantage of network assistance to improve the performance of the ad hoc neighbor discovery algorithms in terms of energy efficiency, resource utilization, discovery time and discovery rate. To address the equirements of different applications and types of devices, two design objectives are studied in this work. The first one is discovery time prioritized without energy limitation, while the other is constrained to using a certain amount of energy. We distinguish five levels of network involvement from allowing for synchronization to explicitly providing information on the used peer discovery resources. The analysis in this work indicates that the setting of transmission probability for devices, which depends on system load, plays a critical role in the process of D2D discovery. Furthermore, stopping the devices which have already been discovered by enough candidates can improve the performance, in terms of reducing the interference to other devices and saving energy consumption. It is also shown in the simulation results that, to reach a given quantity of D2D communication candidates for all the devices in the area of study, the discovery time as well as the energy consumption can be reduced up to 87-91% from the lowest level of the network assistance to the highest level.

In this thesis we study a classical problem of the electrical field; the optimal power flow (OPF) in an electrical network. Given a power grid, the problem is to find the optimal production of generators respecting all the constraints imposed by physics, like Kirchhoff’ equations and power bounds on each part of network. The goal of a power flow problem is to obtain complete voltage angle and magnitude information for each bus in a power system for operating conditions.Solving this problem in a centralized manner for a very large networks becomes difficult due to computational limitations and become undesirable due to safety reasons. The development of computational ability in each component of the network has opened new horizons, linking the electrical and ICT engineering. With the rapid development of smart grid infrastructures, the OPF problem is becoming very important.Scalability and the fast convergent properties of the associated solution methods are highly desirable in a practical point of view. One of the main challenge in the OPF problem is the decoupling of the constraints enforced by the Kirchhoff’ laws. Our contribution has been to propose a new formulation of the problem so that the bigger problem can be decomposable into a number of subproblems (one for each node), which relies on only the local information available. As a result, our proposed protocols are scalable. Moreover, we adopt the state-ofthe-art alternating direction method of multipliers (ADMM), which blends fast convergent properties into the proposed protocol. We also propose a partially distributed protocol based on ADMM, which relies on an intelligent central controller to handle the associated constraints of the OPF problem. In this case, the computational burden at nodes are very small, thus, the nodes can be unintelligent. Finally, we provide numerical experiments to illustrate the behavior of proposed algorithms.

Anaesthesia devices are a critical part of the medical equipment in any hospital. Safe operation of these devices is of the highest importance to the lives of the patients. To ensure this, the device has to detect when a component is malfunctioning. During development, the device is tested to insure that possible errors are detected, reported and that the device reacts properly. This thesis was performed at Dräger Medical, in Lübeck, Germany, to analyze and attempt to improve the development of anaesthesia devices. In the anaesthesia device, the gas mixer unit consists of several valves and pressure sensors whose function is to deliver the correct gas mixture to the patient. To verify that any malfunctions in the components are detected correctly, errors are simulated in a laboratory setting. This simulation of malfunctioning valves and pressure sensors is currently done manually at Dräger Medical. This manual procedure is very time-intensive, and limited in terms of complexity and the accuracy. To reliably and cost-effectively test for errors, an automated test procedure would be preferred. Such a procedure is able to perform complex test during extended periods of time. The repeatability and the accuracy can also be higher. A new approach using a computer that controls the simulation hardware was developed. The hardware needs to be able to manipulate the valves and pressure sensors in the mixer and accept commands from a computer to facilitate complex automatic testing. For this purpose, a 32-bit microcontroller with appropriate connectivity was chosen. For sensor manipulation, several modules controlled by the microcontroller were designed and assembled. For communicating with the microcontroller, a graphical user interface was designed in LabVIEW. This offers the operator full manual control over the simulation hardware as well as the possibility to automate the testing procedure through the use of scripts. These scripts are executed by an internal script engine and the results are automatically compiled into a report for documentation purposes. The new system has significantly improved the ability to test anaesthesia devices. Automatic testing can now be done from a normal desktop computer. Compared to the old method of manually testing one signal at a time, the operator is now able to simultaneously manipulate several signals. If no automatic control is necessary, the combination of a computer and microcontroller still offers superior accuracy and flexibility compared to the old method.

Indoor positioning is a technique that is used to locate a mobile device in indoor environment in real or near real-time. The demand for indoor positioning system as a location based system is becoming more and more widespread. However, the field has not gain much success as outdoor positioning system. The objective of this thesis work is to design and implement an indoor positioning system that relies on ultra wide band technology. The report also describes the way how to implement IEEE802.15.4a physical layer and medium access layer .The system uses time difference of arrivals technique to estimate the position of the mobile device. Through an evaluation of our system, we conclude that ranging can reach an accuracy of ±20cm in line of sight measurement and ± 50cm for non-line of sight measurement. But the localization that is achieved has an accuracy is up to ±1.1m, we believe this can be improved by having all device to be synchronized effectively.

This master thesis covers the seasonal planning of a small scale hydropower system. The system in this study is owned and operated by Mälarenergi Vattenkraft AB. The total system consists of 4 different main rivers with 24 hydropower stations and several dams. The total installed power in the system is 43.75 MW. Most of the hydropower stations are regarded as small scale hydropower stations and thus entitled to green certificates. In this report the issue of planning is formulated as an optimization problem. The objective is to maximize the revenue during a given period, while considering hydrological couplings, physical and legal limitations. To provide some orientation and background to the problem the first chapters in the report cover hydropower, system planning, the electrical market and optimization. An essential part of the work consists of modeling of hydropower systems and two different models are accomplished. Both models include delay time and maximum discharge changes among other things. The first model is a mixed integer linear model (MILP) where the power production is expressed in integers and continuous variables. Minimal discharge, prohibited intervals and non decreasing marginal production equivalent are also included. The second model is a nonlinear model (NLP) that in contrast to the first model includes simplified head dependence. On the other hand some other property must be left out. To solve the optimization problem mathematical programming in GAMS is used. In GAMS the described models and the basic numerical data for the system can be formulated and optimized. A number of test cases with different conditions are made to study how the system could be run optimally and what factors that can be identified as important. The results of the simulations are extensive and an interesting selection of these are analyzed and presented in the report.