The thesis describes the design and implementation of an interprocess communication (IPC) mechanism within a real-time distributed operating system kernel (RT-DOS) which is designed for a transputer-based network. The requirements of real-time operating systems are examined and existing design and implementation strategies are described. Particular attention is paid to one of the object-oriented techniques although it is concluded that these techniques are not feasible for the chosen implementation platform. Studies of a number of existing operating systems are reported. The choices for various aspects of operating system design and their influence on the IPC mechanism to be used are elucidated. The actual design choices are related to the real-time requirements and the implementation that has been adopted is described.

We examine which capabilities technologies provide to support collaborative process modeling. We develop a model that explains how technology capabilities impact cognitive group processes, and how they lead to improved modeling outcomes and positive technology beliefs. We test this model through a free simulation experiment of collaborative process modelers structured around a set of modeling tasks. With our study, we provide an understanding of the process of collaborative process modeling, and detail implications for research and guidelines for the practical design of collaborative process modeling.

This thesis introduces low-cost implementations for the next generation distributed antenna system (DAS) using analogue radio over fibre. A multiple-input-multiple-output (MIMO) enabled radio over fibre (RoF) system using double sideband (DSB) frequency translation system is proposed. In such a system, the 2x2 MIMO signals can be transmitted to the remote antenna units (RAUs) from the base station via a single optical link. By using the DSB frequency translation, the original single-input-single-output (SISO) DAS can be upgraded into the MIMO DAS without implementing parallel optical links. Experimentally, the DSB frequency translation 2x2 MIMO RoF system transmits 2x2 LTE MIMO signals with 20MHz bandwidth in each channel via a 300m MMF link. The condition number of the system is < 10dB within the power equaliser bandwidth which means the MIMO system is well-conditioned and the crosstalk between the channels can be compensated by the MIMO signal processing. To install the DSB frequency translation system in a wideband service-agnostic DAS, the original MIMO signals need to be translated into unoccupied frequency bands over the DAS, which are usually occupied by specific applications that are not to be transmitted over the DAS. The frequency spectrum allocation of the wireless services is analysed showing that by choosing a particular LO frequency (2.2GHz in the UK), in the DSB frequency translation system, the original MIMO signals can always be translated into unoccupied frequency bands so that the same infrastructure can support multiple services. The idea of DSB frequency translation system can not only support MIMO radio over fibre but can also improve the SFDR of a general radio over fibre system. Because when the upper sideband and the lower sideband of the signal after translation are converted back to the original frequency band, the noise adds incoherently but the signals add-up coherently, this gives the system theoretically 2dB 3rd order SFDR improvement. If the idea of the DSB frequency translation is extended into a higher number of sidebands, the system SFDR can be further improved. Experimentally, the system 3rd order SFDR can be improved beyond the intrinsic optical link by 2.7dB by using quadruple sideband (QSB) frequency translation. It means the optical bandwidth in a general RoF system can be traded for the electrical SFDR. By integrating the analogue and the digital RoF systems, a hybrid DAS has been demonstrated, showing that the EVM dynamic range for the 4G LTE service (using digital RoF link) can be improved to be similar to the 3G UMTS service (using analogue RoF link), so that fewer number of RAUs for the LTE services are needed.

abstract: Distributed wireless sensor networks (WSNs) have attracted researchers recently due to their advantages such as low power consumption, scalability and robustness to link failures. In sensor networks with no fusion center, consensus is a process where all the sensors in the network achieve global agreement using only local transmissions. In this dissertation, several consensus and consensus-based algorithms in WSNs are studied. Firstly, a distributed consensus algorithm for estimating the maximum and minimum value of the initial measurements in a sensor network in the presence of communication noise is proposed. In the proposed algorithm, a soft-max approximation together with a non-linear average consensus algorithm is used. A design parameter controls the trade-off between the soft-max error and convergence speed. An analysis of this trade-off gives guidelines towards how to choose the design parameter for the max estimate. It is also shown that if some prior knowledge of the initial measurements is available, the consensus process can be accelerated. Secondly, a distributed system size estimation algorithm is proposed. The proposed algorithm is based on distributed average consensus and L2 norm estimation. Different sources of error are explicitly discussed, and the distribution of the final estimate is derived. The CRBs for system size estimator with average and max consensus strategies are also considered, and different consensus based system size estimation approaches are compared. Then, a consensus-based network center and radius estimation algorithm is described. The center localization problem is formulated as a convex optimization problem with a summation form by using soft-max approximation with exponential functions. Distributed optimization methods such as stochastic gradient descent and diffusion adaptation are used to estimate the center. Then, max consensus is used to compute the radius of the network area. Finally, two average consensus based distributed estimation algorithms are introduced: distributed degree distribution estimation algorithm and algorithm for tracking the dynamics of the desired parameter. Simulation results for all proposed algorithms are provided. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

Made available in DSpace on 2014-06-12T15:49:34Z (GMT). No. of bitstreams: 1 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / O processamento de consultas tem sido abordado como um problema central em ambientes dinâmicos e distribuídos. O ponto crítico do processamento, no entanto, é a reformulação da consulta submetida em um ponto origem em termos de um ponto destino, considerando as correspondências existentes entre eles. Abordagens tradicionais, em geral, realizam a reformulação utilizando correspondências de equivalência. Entretanto, nem sempre conceitos de um ponto origem têm correspondentes equivalentes no ponto destino, o que pode gerar uma reformulação vazia e, possivelmente, nenhuma resposta para o usuário. Neste caso, se o usuário considera interessante receber respostas relacionadas, mesmo que não precisas, é melhor gerar uma reformulação adaptada ou enriquecida e, por consequência, respostas aproximadas, do que nenhuma. Dentro deste escopo, o presente trabalho propõe um enfoque baseado em semântica, denominado SemRef, que visa integrar técnicas de enriquecimento e reformulação de consultas de forma a prover usuários com um conjunto de respostas expandidas. Reformulações exatas e enriquecidas são produzidas para permitir alcançar esse conjunto. Para tal, usamos semântica obtida principalmente de um conjunto de correspondências semânticas que estendem as normalmente encontradas na literatura. Exemplos de correspondências não usuais são closeness e disjointness. Além disso, usamos o contexto do usuário, da consulta e do ambiente como meio de favorecer o processo de reformulação e lidar com informações que somente são obtidas dinamicamente. Formalizamos as definições propostas através da Lógica Descritiva ALC e apresentamos o algoritmo que compõe o enfoque proposto, garantindo, através de propriedades aferidas, sua corretude e completude. Desenvolvemos o algoritmo SemRef através de um módulo de submissão e execução de consultas em um Sistema de gerenciamento de dados em ambiente P2P (PDMS). Mostramos exemplos que illustram o funcionamento e as vantagens do trabalho desenvolvido. Por fim, apresentamos a experimentação realizada com os resultados que foram obtidos

Context: Global software development is the emerging trend in today’s world as it provides the software companies with certain advantages like access to skill and cheap labor, low development cost etc. There are also many challenges and risks involved in globally distributed software project as compare to co-located projects like communication, coordination and control etc. due to geographical separation. There is also a recent interest in applying agile methods in offshore projects in order to minimize certain offshore challenges. Agile methods in collocated environment demands high communication, coordination and collaboration between the team members. However implementing agile methods in distributed environment is beneficial and challenging too, because of inherited GSD challenges. Therefore, it is necessary to carefully understand the benefits and challenges of applying agile methods in distributed project before actually initiating the development. Objectives: This research study aims to look at current empirical evidence regarding benefits and challenges of applying agile methods in offshore projects, in order to understand it properly. Furthermore, we have examined that which of the benefits and challenges reported in literature can be seen in practice. This helped us in finding out the similarities and differences between the benefits and challenges that are reported in literature and in practice. Methods: To fulfill our aims and objectives we have first conducted the detailed systematic review analysis of the empirical studies from year 2000-2010. The systematic review approach helped us to collect and summarize the empirical data available regarding the benefits and challenges of applying agile methods in offshore projects. The research studies were identified from the most authentic databases that are scientifically and technically peer reviewed such as Inspec and Compendex, IEEE Xplore, ACM digital library, Springer Link, Science Direct, Google Scholar, Scopus, ISI Web of Knowledge and Willey Inter Science Journal Finder. Furthermore, industrial survey was conducted in order to identify whether the benefits and challenges enlisted in literature can be confirmed by practitioners. This helped us in determining the similarities and differences between benefits and challenges that are reported in empirical literature and industrial survey. Results: From systematic review results, we have found the list of benefits and challenges of most applied agile practices such as daily scrum meetings, sprint planning meetings, sprint review meetings, retrospective meetings, pair programming, short release and on-site customer. The most common benefits related to above identified agile practices are early problem identification, project visibility, increase communication, coordination and collaboration, trust, clarification of work and requirements, early client feedback and customer satisfaction. Similarly the most common challenges associated with above identified agile practices are lack of linguistic skills, culture differences and temporal differences. From survey result, it was found that the majority of benefits and challenges identified through literature review are prevalent in software industries to some extent. We were able to identify the benefits and challenges of agile practices such as daily scrum, sprint planning meetings, sprint review, retrospective meetings and short release. The most common benefits of above identified agile practices highlighted by survey participants are project visibility, early problem identification, increase coordination, opportunity for knowledge sharing and transferring, immediate feedback from client, and opportunity for understanding the task properly. Similarly the most common challenges identified by survey participants are language problems, temporal difference and difficult to explain and understand problems or issues over communication technologies. However, there are certain challenges like trust and culture issues, which have received most attention in the empirical literature, but are not identified by majority of industry respondents. Conclusions: From the information attained so far regarding the benefits and challenges of agile methods in offshore projects, we observed that there is an emerging trend of using agile methods in offshore projects and practitioners actually found it beneficial. The benefits of agile practices does not achieve straightaway there are certain challenging factors of GSD too, which can restrict the implementation or make the methodology not useful such as communication, coordination and collaboration. These challenges are usually occurred due to geographical separation, lack of trust and linguistic skills, culture difference etc. The presented work add contribution in a sense as to the best of our knowledge no systematic review effort has been done in this area with specifically focuses on highlighting the benefits and challenges. From survey results we found that majority of benefits and challenges highlighted by survey participants are to some extent same with what we have already studied in literature. However there are certain important challenges which have received most attention in empirical literature but were less identified by the survey participants like trust issue and culture difference. The benefits and challenges identified through industrial survey do not add much information into our attention. This does not mean that all possible benefits and challenges of applying agile methods in offshore project have been explored. The responses which were received from industry practitioners were quite few to make any kind of arguments. There is a probability that we missed the important benefits and challenges related to particular agile practices during our industrial survey. Therefore we conclude that a much thorough and inclusive answers should be required to identify the benefits and challenges of applying agile methods in offshore projects.

Companies around the world work more globally than ever and it reflects in the system development projects that run. The companies work span continents and the employees work together over the borders. This way of working, the global distributed, brings a number of opportunities for the company but also presents a lot of problems. The distributed way of working means that the teams and/or individuals are divided. I wanted to connect this way of working with the agile framework Scrum, partly due to my own interest on the subject and partly as it is a contradiction to me, distributed work and Scrum, therefore a challenge to combine. To be able to investigate this way of working I got in touch with two companies that work globally and distributed, using the Scrum technique, I read literature and papers on the subject to be able to reach my conclusions. My conclusions are based on the success factors I found in both the literature and the dialogs performed. The study shows three important qualities in a leader, a scrum master, in a globally distributed development team: Coaching leadership, clear leadership and smaller distributed teams not individuals.

New ways of interaction between users and their computing devices has revealed that users are not only interested in sharing their data, but their user interfaces as well. This calls for an extension of the traditional notion of user interfaces, to a notion where user interfaces span over multiple devices: Distributed User Interfaces (DUIs). The purpose of this thesis is to identify challenges in developing Web based DUIs, and the result is a JavaScript library that aids the development of these types of interfaces. The development has been driven in an explorative fashion, to discover techniques that is appropriate to use, when moving ideas from existing DUI frameworks for the desktop, to the Web. Soundness of the implementation has been evaluated by measuring properties of the library source code that indicates maintainability and extensibility. The conclusion is that the library has the potential of answering the needs for future DUI development targeting the Web.

This dissertation presents and develops the Intelligent Picocell as a solution for high bit rate, efficient bandwidth indoor wireless communication. The research has examined different aspects of the indoor radio propagation environment and system implementation in order to highlight key benefits of the proposed architecture. Explosive growth in demand for indoor wireless communications motivates research into this novel radio architecture. The architecture should be capable of tailoring capacity and coverage to the needs of the specific indoor environment, while maximising spectral efficiency. The Intelligent Picocell is based on an evolution of the distributed antenna concept to provide macrodiversity, microdiversity and interference cancellation. The architecture is fully scalable to large numbers of users and can provide plug-and-play operation, with no need for detailed system planning beyond the antenna locations. The research examines different aspects of picocell system performance and design, including: Investigation on the indoor radio environment. Through measurements, the effects of building features on path loss and shadowing are analysed and propagation models are proposed for simulating picocell systems. Analysis of the Intelligent Picocell architecture, two algorithms are proposed for interference reduction, one based on a distributed narrowband optimum combiner and the other on a dynamic channel assignment and allocation scheme. Through simulation, it was demonstrated that the mobile transmitted power for an Intelligent Picocell is lower than the power required in a distributed antennas system. It was also shown that the capacity of the system depends on the number of antennas distributed in the building. Key words: Intelligent picocell, adaptive antennas, diversity, distributed antennas, dynamic channel allocation, propagation measurements.

In this thesis we develop analytical models for boundary layer flow through a two dimensional group of obstacles , based on the "distributed force" model. An array of obstacles is represented as a region without solid obstructions but with distributed body forces resisting the flow. Linear analyses are presented of inviscid, laminar (or constant eddy viscosity) and turbulent flow through such force distributions. For any group of obstacles, we show how to calculate the model force distribution which becomes the input for the linear analyses. The entire procedure can be iterated to take account of non-linear upstream sheltering effects. In general the model distributed force integrates to equal the actual force exerted by obstacles on the flow divided by the fraction of the array volume not occupied by solid obstacles. Turbulent stresses are modelled using a mixing length that is uniform up to a specified height and increases linearly above. Our physical arguments for a displaced mixing length above the obstacles provide an explanation for the observed coincidence between displacement height and the level of mean momentum absorption. Comparisons of the turbulent analysis results with numerical simulations and experimental data show very encouraging agreement and so support both the distributed force model and the assumptions of the mathematical analysis. From the results of the turbulent flow analysis, effective roughness and displacement heights can be calculated for the flow above the obstacles. When the displacement of the turbulent mixing length is correctly taken into account, the calculated parameters are comparable with those obtained experimentally. An analysis of plume dispersion through a group of obstacles shows how the flow field results can be applied to practical situations, and highlights the dominant effect of enhanced perturbation shear stress, especially in the obstacle roof top layer, on changes to the downstream evolution of the plume.