Many enterprise applications persist data beyond their lifetimes, usually in a database management system. Orthogonal persistence provides a clean programming model for communicating with databases. A program using orthogonal persistence operates over persistent and non-persistent data uniformly. However, a straightforward implementation of orthogonal persistence results in a large number of small queries each of which incurs a large overhead when accessing a remote database. In addition, the program cannot take advantage of a database's query optimizations for large and complex queries. Instead, most programs compose smaller queries into a single large query explicitly and send the query to the database through a command-level interface. These explicit queries compromise the modularity of programs because they do not compose well and they contain information about the program's future data access patterns. Consequently, programs with explicit queries are harder to maintain and reason about. In this thesis, we first define transparent persistence, a relaxation of orthogonal persistence. We show how transparent persistence in current tools can be made more practical by developing AutoFetch. The key idea in AutoFetch is to dynamically observe a program's data access patterns and use that information to reduce the number of queries. While AutoFetch is constrained by existing Java technology and tools, Remote Batch Invocation (RBI) adds the batch statement to the Java language. The batch statement is a general purpose mechanism for optimizing distributed communication using batching. RBI-DB specializes the ideas in RBI for databases. Both of these ideas help bridge the performance gap between orthogonally persistent systems and traditional database interfaces. / text

The pandemic has had significant effects on our society overall. This has meant organizations have been forced to rethink their structure and work arrangement. Our object of study is the imposed and fast changes to work arrangement, our case has been a municipal organization. Employees have been interviewed to give us insight into their experiences of working during these conditions and how they anticipate working in the future. Our results show that the organization has successfully adapted to these changes and become more of a distributed organization that relies heavily on Teams to perform its communication and collaboration tasks. The work arrangement has had positive effects on efficiency; however, this has affected their sociality and their groups have become smaller. The anticipated future seems to be more of a hybrid organization, which allows for both remote work and co-located work. These findings are relevant for organizations going through a similar transformation in order to get insight from our findings to help them in their process.

Unmanned aerial vehicles have developed rapidly in recent years due to technological advances. UAV technology can be applied to a wide range of applications in surveillance, rescue, agriculture and transport. The problems that can exist in these areas can be mitigated by combining clusters of drones with several technologies. For example, when a swarm of drones is under attack, it may not be able to obtain the position feedback provided by the Global Positioning System (GPS). This poses a new challenge for the UAV swarm to fulfill a specific mission. This thesis intends to use as few sensors as possible on the UAVs and to design the smallest possible information transfer between the UAVs to maintain the shape of the UAV formation in flight and to follow a predetermined trajectory. This thesis presents Extended Kalman Filter methods to navigate autonomously in a GPS-denied environment. The UAV formation control and distributed communication methods are also discussed and given in detail.

Verteilte Kommunikationssysteme haben in den letzten Jahren enorm an Bedeutung gewonnen, insbesondere durch die Vielzahl von Anwendungen in unserem Alltag. Die Heterogenität der Anwendungen und Anwendungsdomänen spricht für die Komplexität solcher Systeme und verdeutlicht die Herausforderungen, mit denen ihre Entwickler konfrontiert sind. Der Schwerpunkt dieser Arbeit liegt auf der Unterstützung des Entwicklungsprozesses von Anwendungen für verteilte Kommunikationssysteme. Es gibt zwei Aspekte, die dabei berücksichtigt werden müssen. Der erste und offensichtlichste ist die Unterstützung der Entwicklung der Anwendung selbst, die letztendlich auf der vorhandenen verteilten Kommunikationsinfrastruktur bereitgestellt werden soll. Der zweite weniger offensichtliche, aber genauso wichtige Aspekt besteht in der Analyse der Anwendung vor ihrer eigentlichen Installation. Anwendungsentwicklung und analyse sind also "zwei Seiten der gleichen Medaille". Durch die Berücksichtigung beider Aspekt erhöht sich jedoch andererseits der Aufwand bei der Entwicklung. Die Arbeit kombiniert und erweitert vorhandene Technologien entsprechend dem modellgetriebenen Entwicklungsparadigma zu einer einheitlichen Entwicklungsmethode. Die Eigenschaften der Anwendung werden in einer vereinheitlichten Beschreibung erfasst, welche sowohl die automatische Überführung in Installationen auf echten Infrastrukturen erlaubt, als auch die Analyse auf der Basis von Modellen. Darüber hinaus wird der Entwicklungsprozess mit zusätzlicher Unterstützung bei der Visualisierung der Analyse ergänzt. Die Praktikabilität des Ansatzes wird anschließend anhand der Entwicklung und Analyse einer Anwendung zur Erdbebenfrühwarnung unter Beweis gestellt. / Distributed communication systems have gained a substantial importance over the past years with a large set of examples of systems that are present in our everyday life. The heterogeneity of applications and application domains speaks for the complexity of such systems and the challenges that developers are faced with. The focus of this dissertation is on the development of applications for distributed communication systems. There are two aspects that need to be considered during application development. The first and most obvious is the development of the application itself that will be deployed on the existing distributed communication infrastructure. The second and less obvious, but equally important, is the analysis of the deployed application. Application development and analysis are like "two sides of the the same coin". However, the separation between the two increases the cost and effort required during the development process. Existing technologies are combined and extended following the model-driven development paradigm to obtain a unified development method. The properties of the application are captured in a unified description which drives automatic transformation for deployment on real infrastructures and/or analysis. Furthermore, the development process is complemented with additional support for visualization to aid analysis. The defined approach is then used in the development of an alarming application for earthquake early warning.

In telecommunications, distributed cooperative communications refer to techniques which allow different users in a wireless network to share or combine their information in order to increase diversity gain or power gain. Unlike conventional point-to-point communications maximizing the performance of the individual link, distributed cooperative communications enable multiple users to collaborate with each other to achieve an overall improvement in performance, e.g., improved range and data rates. The first part of this dissertation focuses the problem of jointly decoding binary messages from a single distant transmitter to a cooperative receive cluster. The outage probability of distributed reception with binary hard decision exchanges is compared with the outage probability of ideal receive beamforming with unquantized observation exchanges. Low- dimensional analysis and numerical results show, via two simple but surprisingly good approximations, that the outage probability performance of distributed reception with hard decision exchanges is well-predicted by the SNR of ideal receive beamforming after subtracting a hard decision penalty of slightly less than 2 dB. These results, developed in non-asymptotic regimes, are consistent with prior asymptotic results (for a large number of nodes and low per-node SNR) on hard decisions in binary communication systems. We next consider the problem of estimating and tracking channels in a distributed transmission system with multiple transmitters and multiple receivers. In order to track and predict the effective channel between each transmit node and each receive node to facilitate coherent transmission, a linear time-invariant state- space model is developed and is shown to be observable but nonstabilizable. To quantify the steady-state performance of a Kalman filter channel tracker, two methods are developed to efficiently compute the steady-state prediction covariance. An asymptotic analysis is also presented for the homogenous oscillator case for systems with a large number of transmit and receive nodes with closed-form results for all of the elements in the asymptotic prediction covariance as a function of the carrier frequency, oscillator parameters, and channel measurement period. Numeric results confirm the analysis and demonstrate the effect of the oscillator parameters on the ability of the distributed transmission system to achieve coherent transmission. In recent years, the development of efficient radio frequency (RF) radiation wireless power transfer (WPT) systems has become an active research area, motivated by the widespread use of low-power devices that can be charged wirelessly. In this dissertation, we next consider a time division multiple access scenario where a wireless access point transmits to a group of users which harvest the energy and then use this energy to transmit back to the access point. Past approaches have found the optimal time allocation to maximize sum throughput under the assumption that the users must use all of their harvested power in each block of the "harvest-then-transmit" protocol. This dissertation considers optimal time and energy allocation to maximize the sum throughput for the case when the nodes can save energy for later blocks. To maximize the sum throughput over a finite horizon, the initial optimization problem is separated into two sub-problems and finally can be formulated into a standard box- constrained optimization problem, which can be solved efficiently. A tight upper bound is derived by relaxing the energy harvesting causality. A disadvantage of RF-radiation based WPT is that path loss effects can significantly reduce the amount of power received by energy harvesting devices. To overcome this problem, recent investigations have considered the use of distributed transmit beamforming (DTB) in wireless communication systems where two or more individual transmit nodes pool their antenna resources to emulate a virtual antenna array. In order to take the advantages of the DTB in the WPT, in this dissertation, we study the optimization of the feedback rate to maximize the energy efficiency in the WPT system. Since periodic feedback improves the beamforming gain but requires the receivers to expend energy, there is a fundamental tradeoff between the feedback period and the efficiency of the WPT system. We develop a new model to combine WPT and DTB and explicitly account for independent oscillator dynamics and the cost of feedback energy from the receive nodes. We then formulate a "Normalized Weighted Mean Energy Harvesting Rate" (NWMEHR) maximization problem to select the feedback period to maximize the weighted averaged amount of net energy harvested by the receive nodes per unit of time as a function of the oscillator parameters. We develop an explicit method to numerically calculate the globally optimal feedback period.

Collaborative design inträffar när flera aktörer samarbetar för ett gemensamt mål eller intresse som inte kan åstadkommas ensamt. Collaborative design sker antingen i ett co-located möte ”ansikte mot ansikte” eller distribuerat möte ”distansmöte”. Distribuerade möten, oftast via ett nätverkssystem, sker då olika aktörer av ett projekt inte befinner sig i närheten av varandra. Målet med distribuerad kommunikation är att kunna återskapa det fysiska mötet i ett virtuellt möte.  Syftet med denna studie är utveckling av en kommunikationsmetod som med hjälp av förstärkt verklighet kan visualisera och överföra information mellan arkitekt och beställaren i ett distribuerat möte. Metoden baseras på mjukvaruutveckling i spelmotorer vilka har kapacitet för skapande av realtidsvisualiseringar i kombination med flera skript som kan utföra många komplexa funktioner, inklusive synkron dataöverföring. Då examensarbetet fokuserar på distribuerad kommunikation har mjukvaruutvecklingen begränsats till endast smarta mobiltelefoner, detta på grund av stora tillgängligheten till enheten i allmänheten. Ett ytterligare syfte är undersökning om hur överföring av BIM kan simplifieras och automatiseras till spelmotorn Unity.  Utvecklingen av demonstratorn visar att BIM-överföring kan ske via scheman skapade i BIMmjukvaror såsom Autodesk Revit som inläses av skript i Unity. Överföringsmetoden visualiserar BIM i realtid och även skapandet av funktioner som integrerar BIM, inklusive våningsplanväljare och lagervisningsväxlare. Systemet för nätverkssynkronisering möjliggör synkron kommunikation mellan alla aktörer genom användande av funktioner och flera skript som möjliggör positionssynkning, skärmdelning och objektdelning. Resultatet från studien gällande förstärkt verklighet har kombinationen av fördelar och nackdelar varierade beroende på aktörernas erfarenhet. Den utvecklade mjukvaran med tillhörande metod visar på potential för användning gällande distribuerad kommunikation. / Collaborative design occurs when individuals work together to achieve a common goal or interest that cannot be accomplished alone. Collaborative design take place either in a co-located meeting “face to face” or a distributed meeting “distance meeting”. Distributed meetings, often via a networking system, occur when individuals of a project don’t have the opportunity for a colocated meeting. The goal of distributed communication is to be able to recreate the physical confrontation in a virtual meeting.  The purpose of this study is to develop a communication software that, with addition of augmented reality, can visualize and share information between architects and clients in a distributed meeting. For software development game engine Unity is used, which has the capacity to create a real-time visualization in combination with scripts that can add features such as synchronous data transfer. As the thesis focuses on distributed communication a limitation has been put on used devices to only consider smartphones, this is due to the high level of availability of the device in general. An additional purpose of the thesis is to simplify and automate BIM transfer to Unity game engine. The development of a demonstrator shows that BIM transfer can be done via usage of schedules that can be created in BIM software such as Autodesk Revit, which is later read by scripts in Unity. The software visualizes BIM in real time and supports creation of functions that can integrate with BIM, including plan selector “våningsplanväljare” and layer manager “lagervisningsväxlare”. The network synchronization system enables synchronous communication between all users, using functions such as position sync, screen sharing and object sharing. There has been a combination of advantages and disadvantages for augmented reality that varied depending on individual experience. The developed software with methods has potential for usage in use of distributed communication.

Es wird ein Kommunikationsschema vorgestellt, das auf Basis von regelmäßigen, dezentral organisierten Gitterstrukturen anonyme Kommunikation unter den Gitterknoten ermöglicht. Für den Empfänger einer Nachricht ist nicht ersichtlich, wer die Nachricht abgesetzt hat. Ein Angreifer, der die Kommunikation zwischen den Knoten beobachtet, kann zwar erkennen, dass Nachrichten zugesellt, vermittelt und empfangen werden, jedoch ist es ihm nicht möglich, festzustellen, welche Nachricht für welchen Teilnehmer vorgesehen ist.

Es wird ein Kommunikationsschema vorgestellt, das auf Basis von regelmäßigen, dezentral organisierten Gitterstrukturen anonyme Kommunikation unter den Gitterknoten ermöglicht. Für den Empfänger einer Nachricht ist nicht ersichtlich, wer die Nachricht abgesetzt hat. Ein Angreifer, der die Kommunikation zwischen den Knoten beobachtet, kann zwar erkennen, dass Nachrichten zugesellt, vermittelt und empfangen werden, jedoch ist es ihm nicht möglich, festzustellen, welche Nachricht für welchen Teilnehmer vorgesehen ist.