Received Signal Strength Indication (RSSI) fingerprinting is a popular technique in the fieldof indoor positioning. Many studies on the subject exist acknowledging Wi-Fi signal variationconnected to Wi-Fi signals, but does not discuss possible signal variation created byconnected devices nor consequential precision loss.Understanding more about the origins of signal variation in received signal strength indication(RSSI) fingerprinting would help deal with or prevent them as well as provide moreknowledge for applications based on such signals. Environments with a varying number ofconnected devices would benefit from knowing changes in localization precision resultingfrom the devices connecting and disconnecting from the access point because it wouldindicate whether workarounds for such circumstances would be necessary.To address this issue, the work presented here focuses on how the precision of RSSIfingerprinting vary given different levels of connected Wi-Fi devices. It was carried out byconducting real world experiments at times of low- and normal levels of connected devices toaccess points on two separate locations and evaluating precision changes between statedactivity levels. These experiments took place at the University of Borås as well as at Ericssonin Borås.Experimental findings indicate that the accuracy does deteriorate in higher levels of activitythan in low activity, even though not enough evidence to determine the precision ofdeterioration. The experiments thereby provide a foundation for location-based applicationsand services that can communicate the level of positional error that exist in differentenvironments which would make the users aware but also make the applications adaptaccordingly to different environments. Based on the precision achieved, we identify variousapplications that would benefit from our proposed model. These were applications that wouldtrack mobile resources, find immobile resources, find the movement flows of users as well asnavigation- and Wi-Fi coverage applications.Further research for investigating the exact correlation between access point stress andprecision loss is proposed to fully understand the implications connected devices have onRSSI fingerprinting.

This thesis covers the security testing of a system with connected devices. In a world with an ever-growing number of connected devices, it is crucial to be mindful of the consequences unprotected systems can cause. The thesis aim to shine light on the issues of not having sufficient security measures in place. The test target was a system with a battery charger, gateway and cloud service. The testing was done with two different approaches, penetration testing and threat modelling, covering different parts of the system. Only a small fraction of the system was exploited in the report and overall the security was deemed to be alright. The main vulnerabilities found were that the username and password were found unencrypted when attempting to log into the gateway. The traffic between the battery charger and the gateway was also unencrypted and possibly vulnerable to replay attacks. For evaluation of the penetration testing and threat modelling there were found to be advantages and disadvantages to both methods. For a thoroughly analysis of the methods it would have needed further investigation. The system itself has potential for valuable findings with further investigations as well. / Denna rapport inkluderar säkerhetstestning av ett system med uppkopplade enheter. Antalet uppkopplade enheter (Sakernas Internet) runt om i världen fortsätter att växa med hög hastighet. Det är av stor vikt att se till att enheterna i dessa system har de säkerhetsåtgärder som krävs. Att belysa detta problem är ett utav målen med denna rapport. I rapporten testas ett batteriladdarsystem med tillhörande gateway och cloud-tjänst. Testen utfördes med två olika metoder, penetrationstest och hotmodellering, uppdelat på två olika delar av systemet. På grund av de begränsningar som fanns kunde endast en liten del av systemet testas och exploateras. Till största del ansågs säkerheten vara okej. De främsta sårbarheterna som hittades var bland annat okrypterade  användarnamn och lösenord vid försök att logga in på gatewayen. All traffik mellan batteriladdaren och gatewayen var orkypterad och med stor risk för att inte kunna stå emot en replayattack.  Utvärdering av de två metoderna som användes konstaterades för och nackdelar med båda metoderna. För att kunna göra en ordentlig jämförelse av metoderna skulle det behövas en djupare undersökning. Det finns även stort värde i en vidare undersökning av systemet.

This work investigates the voltage scaling feasibility of several low voltage SiC MOSFET modules operated as a single series-connected switch using active gate control. Both multilevel and two-level topologies are capable of achieving higher blocking voltages in high-power converter applications. Compared to multilevel topologies, two-level switching topologies are of interest due to less complex circuitry, higher density, and simpler control techniques. In this work, to balance the voltage between series-connected MOSFETs, device turn-off speeds are dynamically controlled on active gate-drivers using active gate control. The implementation of the active gate control technique (specifically, turn-off dv/dt control) is described in this thesis. Experimental results of the voltage balancing behavior across eight 1.7 kV rated SiC MOSFET devices in series (6 kV total dc bus voltage) with the selected active dv/dt control scheme are demonstrated. Finally, the voltage balancing performance and switching behavior of series-connected SiC MOSFET devices are discussed. / Master of Science / According to ABB, 40% of the world's power demand is supplied by electrical energy. Specifically, in 2018, the world's electrical demand has grown by 4% since 2010. The growing need for electric energy makes it increasingly essential for systems that can efficiently and reliably convert and control energy levels for various end applications, such as electric motors, electric vehicles, data centers, and renewable energy systems. Power electronics are systems by which electrical energy is converted to different levels of power (voltage and current) depending on the end application. The use of power electronics systems is critical for controlling the flow of electrical energy in all applications of electric energy generation, transmission, and distribution. Advances in power electronics technologies, such as new control techniques and manufacturability of power semiconductor devices, are enabling improvements to the overall performance of electrical energy conversion systems. Power semiconductor devices, which are used as switches or rectifiers in various power electronic converters, are a critical building block of power electronic systems. In order to enable higher output power capability for converter systems, power semiconductor switches are required to sustain higher levels of voltage and current. Wide bandgap semiconductor devices are a particular new category of power semiconductors that have superior material properties compared to traditional devices such as Silicon (Si) Insulated-Gate Bipolar Junction Transistors (IGBTs). In particular, wide bandgap devices such as Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) have better ruggedness and thermal capabilities. These properties provide wide bandgap semiconductor devices to operate at higher temperatures and switching frequencies, which is beneficial for maximizing the overall efficiency and volume of power electronic converters. This work investigates a method of scaling up voltage in particular for medium-voltage power conversion, which can be applied for a variety of application areas. SiC MOSFET devices are becoming more attractive for utilization in medium-voltage high-power converter systems due to the need to further improve the efficiency and density of these systems. Rather than using individual high voltage rated semiconductor devices, this thesis demonstrates the effectiveness of using several low voltage rated semiconductor devices connected in series in order to operate them as a single switch. Using low voltage devices as a single series-connected switch rather than a using single high voltage switch can lead to achieving a lower total on-state resistance, expectedly maximizing the overall efficiency of converter systems for which the series-connected semiconductor switches would be applied. In particular, this thesis focuses on the implementation of a newer approach of compensating for the natural unbalance in voltage between series-connected devices. An active gate control method is used for monitoring and regulating the switching speed of several devices operated in series in this work. The objective of this thesis is to investigate the feasibility of this method in order to achieve up to 6 kV total dc bus voltage using eight series-connected SiC MOSFET devices.

With the constant growth of units connected to the internet, it’s becoming more and more common for private persons to get these units into their homes. With easier accessibility to smart units that can be connected straight to your smart home, and at the same time can make your everyday life easier, may also be the greatest securityrisk of your life. The focus of this essay is about the internet of things-units (IoT-units) that’s considered a large securityrisk. This work is made as a quantitative study about security deficiencies among private persons regarding IoT-units. The data produced from this work can be used as an answer of what a private person needs to be more vigilant of when it comes to IoT-units, and also what actions the manufacturing industry need to take for the connected community to be secured. To delve into this, we have chosen to use the methods literature study and a questionnaire study that will be performed to obtain data to answer our questions. Analysis has been made about what can be seen as an IoT-unit, what security deficiencies there are and then account for how to counteract these risks with help of knowledge. The result of the answers from the surveys and the picture we have received after a search for a sustainable and a more secure solution is that some knowledge exists, although not to the extent needed. The conclusion that can be drawn after the analysis of surveys and in the previous research how it should proceed in the current situation is that significantly more resources need to be spent on the right information for the right purpose, when it comes to this important IT-related issue.