In cellular networks, the roaming interconnection was designed when there were only a few trusted parties and security was not a major concern or design criteria. Most of the roaming interconnections today are still based on the decades-old SS7 and the lack of security is being blamed for several vulnerabilities. Recent research indicates that the roaming interconnection has been widely misused for gaining access to the core network. Several attacks have been demonstrated by malicious attackers and other unauthorized entities such as intelligence agencies by exploiting the SS7 signaling protocol. Some operators moved to the more modern LTE (Long Term Evolution) and Diameter Signaling for high-speed data roaming and enhanced security. While LTE offers very high quality and resilience over the air security, it still requires special security capabilities and features to secure the core network against attacks targeting the roaming interconnection. This thesis analyses and identifies attacks that exploit the roaming interconnection and Diameter signaling used in LTE networks. The attacks are analyzed in accordance with the mobile network protocol standards and signaling scenarios. The attacks are also implemented in a test LTE network of a global operator. This thesis also focuses on potential countermeasures to mitigate the identified attacks.

Base station antennas for next generation mobile communication networks will be required to have a wide bandwidth for compatibility and support multi-beam applications. Antenna arrays are one possible candidate for a next generation base station antenna since they can obtain high directivity, support multi-beam and wide angle scanning. However, a wide-band antenna array faces several problems at the low frequency limit. The electrical size of the antenna array becomes smaller at the low frequency and it becomes harder to obtain high directivity. Another issue is that the bandwidth becomes narrower for electrically small antenna arrays under superdirectivity constraints. The Q-factor is a measure of losses and is proportional to the ratio of the stored energy to the dissipated power. It is also inversely proportional to the fractional bandwidth of an antenna array when Q ≫ 1. In this thesis, we investigate the relation between the Q-factor and the directivity and extend our analysis to a superdirective antenna array. The model we are using is based on the antenna designed for base station applications with the frequency range from 700MHz to 4.2GHz and we assume that it is placed over an infinite ground plane. We calculate the Q-factor at 745MHz, which is the center frequency of GSM 700MHz bands using convex optimization. Here, we use the CVX as the convex optimization tool, which can be easily integrated with MATLAB. The expressions of the stored energy and the radiated power are formulated in a matrix form based on the Method of Moment (MoM) using Rao-Wilton-Gilson (RWG) basis functions for the convex optimization. We show the trade-off between the directivity and the Q-factor, or the bandwidth at the low frequency limit. The results are investigated forth cases; one is a vertical model, where each array elements is placed vertically above an infinite ground plane, and the other is a horizontal model, where each array elements is placed horizontally. We show that the Q-factor is slightly lower for the vertical case than the horizontal case. / Nästa generations basstationsantenner för kommunikationsnätverk förväntas hantera flera frekvensband och en metod för detta är att de har stor bandbredd, de förväntas också stödja funktionalitet för multi-beam tillämpningar. Gruppantenner är en möjlig kandidat som både kan erbjuda hög riktverkan hos fjärrfältet, och som har multi-beam kapacitet och möjligheter till vidvinkelscanning. Sådana bredbandiga gruppantenner blir elektriskt små i deras lågfrekvensgräns, och detta ger flera utmaningar på deras funktionalitet för låga frekvenser. Sådana utmaningar är bland annat att få hög riktverkan i deras fjärrfält vid de låga frekvenserna. Strömmar på en elektriskt liten antenn som genererar hög direktivitet (riktverkan) har liten bandbredd, dvs strömmen på den givna geometrin måste förändras mycket som funktion av frekvensen för att bibehålla hög direktiviteten. Q-faktorn är ett mått på förhållandet mellan den upplagrade energin genom den utstrålade effekten. Den år också omvänt proportionell mot den relativa bandbredden när Q ≫ 1. I denna avhandling undersöker vi sambandet mellan Q-faktorn och diriktiviteten hos två konfigurationer av gruppantennelement framförallt med avseende på superdirektiva gruppantenner. Utifrån en existerande experimentell gruppantenn designad för basstationsapplikationer med start frän 700 MHz upp till 4.2 GHz skapar vi två ideala modeller dar vi antar att gruppantennens element är placerad över ett oändligt jordplan. Vi beräknar den lägsta Q-faktorn för den givna geometrin och given direktivitet vid 745 MHz, vilket är mittfrekvensen för GSM 700 MHz-banden med hjälp av konvex optimering. Här använder vi CVX som den konvexa optimeringsverktyg, som är integrerad med MATLAB. Uttrycken av den upplagrade energin och utstrålad effekt formuleras i en matrisform med hjälp av Metod Moment (MoM) uttryckt med Rao-Wilton-Gilson (RWG) basfunktioner. Denna matris-baserade representation av storheterna blir input till en konvex optimering. Vi best¨ammer en relation mellan direktivitet och Q-faktorn, för dessa geometrier. Detta kan formuleras om som bandbredden vi lågfrekvensgränsen hos gruppantennen.

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The climate crisis is more prevalent today than ever before. Many see a clean, carbonfree, electrification as a must if we are to turn this challenge around. Because more andmore of society runs on electricity there has never been a bigger need for an efficientpower grid.Huge amount of data are gathered from the grid every day and this data holds a lotof information that could help to optimise the power grid. This thesis aimed at investigating how consumption data could be used to understand consumption behaviourswithin the power grid and to try and capture these behaviours with typical customers.Consumption data comes in the form of a time series. In every Swedish house therewill soon be a electricity meter that measures the consumption of the house each hour.This creates a time series of consumption with 24 data points each day. One common,typical behaviour, within the power grid is a peak in consumption during the morninghours when everyone is preparing for work and one in the evening when customers startto arrive home and starts to prepare dinner.The data used in this thesis were based on a geographically restricted area, aroundUppsala, with customers in separate houses and a fuse size of 16 A, 20 A or 25 A. Theanalysed data set held 13997 of Vattenfall Eldistribution customers.One group of customers that are particularly interesting are those that owns an electricvehicle (EV). This is because the charging of the vehicle can be done at power muchlarger than what a normal separate house draws from the grid. In an attempt to gatherinformation about EV owners charging habits, a questionnaire were created and postedto different Swedish EV forums. In total 44 EV owners answered the questionnaire.The method applied in this thesis works by grouping customers based on attributescalculated from the time series of the customers. The attributes calculated within thisthesis were degree of utilization, utilization time, night timeshare of consumption, correlation with aggregated load, correlation with air temperature and load factor. Eachattribute are calculated for winter and summer separately. The k-Mean algorithm isutilised to cluster the customers into ten cluster based on the attributes. The time series of each customer is then scaled down using their daily max and min consumption.Then the correlation between three different percentiles of the time series data of eachcluster are calculated. If the correlation factor is high enough the cluster is said to holdcustomer that consumes according to the pattern described by the 57.5th percentile.Next the correlation between the representative curves of each cluster is calculated toensure that only unique patterns are saved as a typical customer. If the representativecustomer of two clusters show high correlation, they are combined into a new largergroup.iA set of typical customers based on degree of utilization, load factor, correlation andall three combined were created. The results indicate that customers with a low degreeof utilization and a high load factor have a flatter consumption profile. Customers thathave high correlation with aggregated load should be prioritised since they contributemore to the aggregated peak load.Using information from Trafikverket, 68 customers were identified within the original data set as being EV owners. This made it possible to analyse the time series tofind information about their charging behaviour. To find charging events, consecutivehours were analysed to find hours with a difference in consumption of at least 3.7 kWh.Of the 68 analysed, 39 showed more than 20 charging events during 2020. The mostpopular starting time for charging were 16 o’clock and the most common duration werebetween one and four hours.The method used in this thesis creates typical customers that illustrates a commonconsumption profile of customers within a group. If a typical customer that illustratesconsumption values are desired the customers has to be grouped based on some attributethat describes the amount of electricity that they consume. Creating the typical customers with a smaller sample of customer from the group creates a typical curve thatexhibits more of the randomness that characterises the real consumption profiles.

In electrical devices and integrated circuits, ohmic contacts are necessary and a prerequisite for the current transport over the metal-semiconductor junctions. At the same time, a desired property of the ohmic contacts is to not add resistance or in other way disturb the performance. For high temperature electronics, the material demands are high regarding functionality and stability at elevated working temperatures, during and after temperature cycling and during long time of use.  Silicon carbide, SiC, is a suitable substrate material for fabrication of high temperature electronics with a large band gap, good thermal conductivity and chemical inertness. The large bandgap causes however difficulties in finding a common material for ohmic contacts to both n- and p-type SiC. The goal of this project is to find a suitable metallization for n- as well as p-type contacts to epitaxially doped SiC for use in integrated circuits. The circuit technology developed and used in KTH for SiC is built on bipolar junction transistors. The p-doped base layer in the transistors is relatively low doped; 5 x 1017 – 1 x 1018 cm-3. P-type SiC is more difficult to form ohmic contacts to than n-type SiC, with such a low doping concentration it is even more complicated.  Today, the metallizations used in the contacts consists of Ni for n-type contacts and Ni/Ti/Al to p-type SiC. Experiments of the specific contact resistivity ρc and the sheet resistance Rsh of these contacts, characterized to two types of samples, are presented for the extreme temperature range of -40 °C – 500 °C. Ohmic contact test chips with transfer length method structures have been compared to similar test structures on samples from the KTH SiC integrated circuits. The metals were also tested on the opposite doping polarity.  Sputter deposition of Co and Si in layers to form CoSi2 contacts was made to chips from the same contact test wafer for comparison with the behavior of the presently used contacts. Since this was a new metallization, the process development of the high temperature anneal and contact formation made an important part of the work.  Out of the tested contacts, Ni has been the best for n-SiC and Ni/Ti/Al for p-SiC. None of the three metallizations formed ohmic contacts to both n- and p-SiC. However, the CoSi2 contacts showed specific contact resistivity ρc &lt;4 x 10-6 Ωcm2 at 25 °C and non-linear I-V characteristics but without barriers to p-SiC after voltage sweeps of ± 75V. / <p>QC 20141203</p>

The electricity distribution in Sweden is experiencing aconsiderable change in conditions by the radical change inregulation policy. The Swedish Energy Agency(Energimyndigheten) is introducing a new regulatory model, theNetwork Performance Assessment Model, as the main tool forsupervising the natural monopolies of local electricitydistribution. The new model has interesting and far-reachingconsequences for the involved parties. This thesis investigates the implications of the newregulation and the regulatory tool, in particularly related toIT-investments evaluations in the distribution utilities. Intoday’s utilities, IT-systems are often a vital part ofoperations, ranging from e.g. real-time monitoring andcontrolling of the network to various administrative tasks.Considerable amounts of money are spent on investments toenhance and maintain these IT-systems. The changed regulationand the new regulatory model put a focus, more than ever, onefficient use of utilities’resources, implying a need forsuitable methods to evaluate ITinvestments. In the thesis, the new regulation is described, inparticular the new regulatory model. The model is presented andcentral implications are identified, e.g. in terms of newrequirements put on the utilities and general businessconsequences. As stated, the focus is on implications relatedto IT-systems and investments in these systems. Furthermore, a wide range of IT-investment evaluationmethods are presented and categorized in the thesis, focusingon IT-investment appraisal techniques. The categories rangesfrom methods only considering cash flows of investments to moreelaborate methods, e.g. for considering behavioral sciencesaspects. The thesis outlines and presents categories of methodsas well as examples of individual methods. In the final part of the thesis, suitable IT-investmentevaluation methods, given the implications of the newregulation, are discussed. The implications include both directbusiness related aspects as well as more technical issuesrelated to the IT-investments. It is also concluded that asuitable method need to incorporate both monetary consequencesof the investment as well as a limited number of non-monetary,related to the regulatory model. Key words:Regulation of electricity distribution,IT-investment evaluation methods, Implications of monopolyregulation / QC 20100608

The vertical-cavity surface-emitting laser (VCSEL) is a type of laser diode that emits light from the surface of the chip from which it is manufactured rather than from a cleaved edge as so far has been common for most telecommunication lasers. VCSEL’s low cost, high power efficiency and low power consumption properties make it a very attractive signal source for many applications such as fiber optical communication, optical interconnects, 3D sensing, absorption spectroscopy, laser printing, etc. In this work, we have developed and evaluated new designs and technologies for extending the performance of VCSELs based on the GaAs material system. A novel scheme for single-mode emission from large size VCSELs, with active region size up to 10 μm, is proposed and discussed. Oxide-free designs of the VCSEL structure either based on an epitaxially regrown p-n-p layer or a buried tunnel junction (BTJ) for lateral current confinement are fabricated and characterized; the latter scheme yielding significant dynamic and static performance improvement as compared to epitaxially regrown design. In addition, the first room-temperature operation of a heterojunction bipolar transistor (HBT) 980nm VCSEL, a so-called transistor-VCSEL, is demonstrated. This novel three-terminal operational VCSEL is believed to have the potential for a ultrahigh modulation bandwidth due to altered carrier dynamics in the cavity region. / <p>QC 20140612</p>

Power systems are in a phase of automation where intelligent components and sub-systems are employed to monitor, control and manage the grid. Quantifying the complex consequences on system reliability, from the integration of such automated and semi-automated equipment into the existing grid is important for maintenance optimisation and fault mitigation. This thesis identifies the  advanced approaches in power system reliability analysis with the potential to capture the complications and correlations in modern power grid after reviewing the traditional reliability evaluation methods. A method for modelling the different modes of failures, possible in a substation and feeder architecture along with the probable false tripping scenarios was developed. An improved Reliability Block Diagram based approach was designed to count in the traditionally unaccounted failure cases affecting both the primary grid and the protectionand control equipment. The effect and corresponding trend of additional feeder lines in a radial distribution system on the net interruption rate experienced at load ends of feeders are derived and modelled. Such real-world substation architectures are analysed and the aforementioned trends are compared with those from the practical grid. Thus, the analysis was able to identify and measure the complex hidden failure probabilities due to both unwanted operation of breakers and functional failure of protection systems. The measured probabilities were used to calculate the impact of protection and control equipment on system  reliability. The obtained results were verified by comparing it with the observations by energy researchers on ten years of protection system failure statistics. The application of the model and results, in optimal maintenance planning and power network optimisation are identified as the next step. / <p>QC 20151002</p>

It is often desirable to find the underlying trends in time series data. This is a wellknown signal processing problem that has many applications in areas such as financial dataanalysis, climatology, biological and medical sciences etc. Mean filtering finds a piece-wiseconstant trend in the data while trend filtering finds a piece-wise linear trend. When thesignal is noisy, the main difficulty is finding the changing points in the data. These are thepoints where the mean or the trend changes. We focus on a quadratic cost function with apenalty term on the number of changing points. We use the `1 norm for the penalty termas it leads to a sparse solution. This is attractive because the problem is convex in theunknown parameters and well known optimization algorithms exist for this problem. Weinvestigate the Alternating Direction Method of Multipliers (ADMM) algorithm and twofast taut string methods in terms of computational speed and performance. A well knownproblem is the occurrence of false changing point detection. We incorporate a techniqueto remove these false changing points to the fast mean filtering algorithm resulting in anefficient method with fewer false detections. We also propose an extension of the fast meanfiltering technique to the trend filtering problem. This is an approximate solution that workswell for signals with low noise levels.

The Nordic power system is under continuous development. New productionsources and loads are installed at a high rate and old ones are taken out of operation.This development gradually alters the power system dynamics. The NordicTransmission System Operators (TSOs) have observed that the frequency qualityis gradually decreasing and recognized a number of reasons for this. Theautomatic frequency containment reserve (FCR-N) is in place to keep the electricfrequency within the interval 50 +/- 0.1 Hz during normal operation. Thisfunction is mainly provided by a number of hydropower plants where the turbinegovernor is set to control the discharge in proportion to the measured frequencydeviation. In later years it has been shown that the disturbance damping is verylow in an interval around 1/60 Hz and it is believed that proper tuning of theturbine governors that provide FCR-N can help mitigating this problem. Newregulator settings have been suggested in a recent study performed at Vattenfalland Uppsala University to improve the performance of the FCR-N, yet keepingthe system robust and the wear on participating units at a minimum. It is nowdesired to investigate the possible eects of new governor settings on the overallpower system stability. This thesis work consists of three main parts. First of all, a reduced Nordicpower system model is constructed in Simpow and validated with PMU datafrom the TSO. Secondly, the frequency responses with the newly suggestedgovernor settings have been investigated when introducing a disturbance into thesystem. Thirdly, the eects of the new governor settings on electro-mechanicaloscillations are investigated. In a word, the overall performance for new governorsettings are tested in a large scale power system model in this thesis work. / Det nordiska kraftsystemet ar under standig forandring. Nya produktionskalloroch laster ansluts och gamla tas ur bruk. Detta paverkar gradvis kraftsystemetsdynamik. De nordiska systemoperatorerna (TSOerna) har erfarit att frekvenskvalitetengradvis forsamras, och att det kan nnas era orsaker till detta.Den automatiska primarregleringsreserven (FCR-N) ska halla frekvensen inomintervallet 50 +/-0,1 Hz under normaldrift. Reserven levereras av ett stort antalvattenkraftverk, dar turbinregulatorn reglerar vattenodet genom turbinen proportionelltmot den uppmatta frekvensavvikelsen. Pasenarear har man kunnatvisa att dampningen av storningar med periodtider runt 60 sekunder ar dalig,och man tror att problemet skulle kunna avhjalpas med battre intrimning avturbinregulatorparametrarna. En studie utford pa Vattenfall och Uppsala Universitethar tagit fram ett forslag panya turbinregulatorinstallningar som skaforbattra prestandan i regleringen utan att forsamra systemets robusthet elleroka slitaget pavattenkraftaggregaten. Nu vill man undersoka om de foreslagnainstallningarna kan ha nagon negativ inverkan pakraftsystemets stabilitet. Det har examensarbetet bestar av tre delar. I den forsta delen satts en reduceradmodell av det nordiska elnatet upp i programmet Simpow, och en validering avmodellen gors med hjalp av PMU-data. I den andra delen undersoks frekvenssvaretfran den nya modellen med de foreslagna turbinregulatorinstallningarna. I den tredje delen undersoks de nya turbinregulatorinstallningarnas inverkanpasystemets elektromekaniska oscillationer. Med andra ord satestas i dettaexamensarbete nya turbinregulatorinstallningar i en detaljerad och storskaligkraftsystemmodell.