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This thesis focuses on the development of multiuser access schemes for spectrum sharing systems whereby secondary users that are randomly positioned over the coverage area are allowed to share the spectrum with primary users under the condition that the interference observed at the primary receiver is below a predetermined threshold. In particular, two scheduling schemes are proposed for selecting a user among those that satisfy the interference constraints and achieve an acceptable signal-to-noise ratio level above a predetermined signal-to-noise threshold at the secondary base station. The first scheme selects the user that reports the best channel quality. In order to alleviate the high feedback load required by the first scheme, a second scheme is proposed that is based on the concept of switched diversity where the base station scans the users in a sequential manner until an acceptable user is found. In addition, the proposed scheduling schemes operate under two power adaptive settings at the secondary users that are based on the amount of interference available at the secondary transmitter. In the On/Off power setting, users are allowed to transmit based on whether the interference constraint is met or not, while in the full power adaptive setting, users are allowed to vary their transmission power to satisfy the interference constraint. A special case of the proposed schemes is also analyzed whereby all the users are assumed to be at the same position, thus operating under the influence of independent and identically distributed Rayleigh fading channels. Finally, several numerical results are illustrated for the proposed algorithms where the trade-off between the average spectral efficiency and average feedback load of both schemes are shown.

Bicycle sharing systems (BSS) have emerged as a powerful stimulus to non- motorized travel, especially for short-distance trips. However, the imbalances in the distribution of bicycles in BSS are widely observed. It is thus necessary to reposition bicycles to reduce the unmet demand due to such imbalances as much as possible. This paper formulates a new mixed-integer linear programming model considering the dynamic nature of the demand to solve the repositioning problem, which is later validated by an illustrative example. Due to the NP-Hard nature of this problem, we seek for two heuristics (greedy algorithm and rolling horizon approach) and one exact solution method (Benders’ decomposition) to get an acceptable solution for problems with large instances within a reasonable computation time. We create four datasets based on real world data with 12, 24, 36, and 48 stations respectively. Computational results show that our model and solution methods performed well. Finally, this paper gives some suggestions on extensions or modifications that might be added to our work in the future. / text

Product sharing systems is recently starting to become a more common phenomenon. Carpools exist in more than 40 Swedish towns and both Stockholm and Gothenburg have established bicycle sharing systems. Other products for which sharing systems have been established throughout Sweden are clothing and tools. From the point of view of the consumer, product sharing systems is a form of consumption which can be placed somewhere in between renting and privately owning a product, where the consumers usually pay a membership fee or a monthly fee to have access to the products whenever they need them. The concept is relatively new, and there are many products for which product sharing systems do not exist. As a consequence, previous research in the area is scarce, with the exception of car pools. However, some research discussing product sharing systems in general exists, such as the research by Lamberton & Rose and Mont. In this thesis, previous research is further developed by analyzing what enables and hinders product sharing systems, and for what type of products these systems are suitable. A mix between a quantitative and a qualitative method is used, as both interviews with owners of sharing systems and a questionnaire survey with potential consumers are carried out. To analyze the concept, institutional and behavioral economic theory is used as well as traditional microeconomics. Both the interviews and the survey indicate that the general knowledge of product sharing systems is low and that it is hard in general for companies to reach out to new users. For the consumers, one of the biggest problems is the perceived risk of not having access to the products when they are needed. Another conclusion is that products for which variety is desired, such as clothing and books, that are used frequently, are especially suitable for product sharing systems. / Produktdelningssystem har under de senaste åren blivit ett allt vanligare fenomen. Bilpooler går att finna i över 40 orter runt om i Sverige, och i både Stockholm och Göteborg har cykeldelningssystem upprättats. Övriga produkter som delningssystem har uppkommit för på olika ställen i Sverige är bland annat kläder och verktyg. Ur konsumentens synpunkt kan delningssystemen ses som ett mellanting mellan hyrande och privat ägande, då konsumenterna oftast betalar någon sorts medlemsavgift eller månadsavgift för att få använda en produkt då de har behovet. Konceptet är relativt nytt och för många produkter finns det ännu inga produktdelningssystem. På grund av detta har produktdelning inte behandlats mycket av tidigare forskning, där undantaget är kring bildelning. En del forskning finns dock att hitta som behandlar produktdelning mer generellt, som exempelvis av Lamberton & Rose och Mont. I denna uppsats vidareutvecklas den tidigare forskningen genom att undersöka vad det är som möjliggör respektive förhindrar produktdelningssystemens uppkomst, och för vilka produkter dessa system är mest lämpade. En blandning av kvantitativ och kvalitativ metod används då både intervjuer med ägare av delningssystem och en enkätundersökning med potentiella konsumenter utförs. För att analysera konceptet använder vi oss av institutionell och beteendeekonomisk teori i kombination med traditionell mikroekonomi. Både intervjuerna och enkäterna tyder på att kännedomen om produktdelningssystem är låg och att det är svårt för företagen att nå ut till kunder. För konsumenternas del är ett av de största problemen den upplevda risken att inte ha tillgång till produkterna då de behövs. En annan slutsats som kan dras är att de produkter för vilka variation önskas, exempelvis kläder och böcker, är lämpade för produktdelning under förutsättningen att produkterna används ofta.

Thesis (MBA (Business Management))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Exxaro Resources is a diversified resources company with a commodity portfolio of coal, mineral sands, base metals and industrial minerals. Exxaro acquired Namakwa Sands in 2008 to increase its market share in the mineral sands industry and to exploit synergies within its mineral sands commodity business. Effective knowledge transfer was identified as an important lever to ensure return on investment with the Namakwa Sands acquisition. The objective of this research project was to follow an academic approach to design a theoretical framework for post-acquisition knowledge transfer to exploit synergies within the Exxaro Sands Commodity Business (CB). A qualitative theory building research method was followed to facilitate the research process and the development of the conceptual framework. Primary data was gathered by conducting interviews with role players within the organisation to understand knowledge transfer requirements and barriers within the Exxaro Sands CB. The interviews were also used to obtain insights into the building blocks of a knowledge sharing strategy and practical inputs on initiatives to implement such a strategy within Exxaro Sands operations. Key findings from the interviews, combined with insights from a comprehensive literature review and strategic analysis of the organisation, were used to compile a conceptual framework for post-acquisition knowledge transfer. The framework consists of the following six interrelated constructs: • Strategy and vision: Knowledge sharing objectives must be aligned with the strategy of the organisation and should be communicated in a compelling knowledge sharing vision. • Culture: A culture conducive to knowledge transfer is required to successfully implement a knowledge-sharing programme. Culture also creates the context for social interaction that enables post-acquisition integration. • Change management: Change management is required to communicate the background, methodology and potential benefits of a knowledge-sharing programme. • Knowledge sharing resources: Knowledge sharing resources are responsible for the execution of knowledge transfer activities. Optimum utilisation of organisational resources is required to ensure operational excellence. • Knowledge sharing processes: The processes construct stipulates how knowledge will be shared and is the key mechanism for facilitating, stimulating, measuring and reinforcing knowledge transfer within the organisation. The six steps identified for the Exxaro Sands knowledge sharing process include the identification, prioritisation and benchmarking of key performance indicators, detailed analysis of the gaps, identification of initiatives to close the gaps and ongoing monitoring to track progress. • Knowledge sharing systems: A range of tools, techniques and supporting infrastructure is required to facilitate the knowledge exchange process. The existence of knowledge sharing systems underpins knowledge sharing success, but cannot achieve the aims of knowledge sharing in isolation. This framework clearly illustrates that knowledge sharing is dependent on more than just the interaction between the holders and receivers of knowledge. A formal systematic process is required to derive maximum benefit. The conceptual framework developed in this study adds value by providing this process – customised for the requirements and context of the Exxaro Sands commodity business. It is important to implement this framework in a structured fashion to provide the objectives, guidelines and milestones required for an effective knowledge-sharing programme. / AFRIKAANSE OPSOMMING: Exxaro Resources is ‘n gediversifiseerde mynbou maatskappy met ‘n kommoditeitsportefeulje van steenkool, titanium sand, sink en industriële minerale. Exxaro het Namakwa Sands oorgeneem in 2008 om sy markaandeel in die titanium bedryf te vergroot en om waarde uit die sinergieë met ander besighede binne die titanium sand besigheidseenheid te put. Effektiewe kennisoordrag is geïdentifiseer as ‘n belangrike hefboom om waarde te ontsluit na die oorname. Die doel van hierdie navorsingsprojek was om ‘n akademiese benadering te volg om ‘n teoretiese raamwerk te skep vir kennisoordrag wat maksimum waarde kan ontsluit binne die Exxaro Sands Kommoditeit Besigheid. Die gekose navorsingsmetodiek was kwalitatiewe teorie bou. Dit is gebruik om beide die navorsingsproses te fasiliteer en om die konsepsuele raamwerk te ontwikkel. Primêre data is ingesamel deur onderhoude te voer met belangrike rolspelers in die organisasie, wat lig gewerp het op kennisoordrag-vereistes en struikelblokke. Die onderhoude het ook die hoeksteen gevorm vir die kennisoordrag-strategie, en het praktiese insette gelewer oor hoe om die strategie te implementeer by Exxaro Sands. Kritiese bevindinge van die onderhoude, saam met insig uit ‘n omvattende literatuurstudie en strategiese analise van die besigheid is gebruik om die raamwerk vir kennisoordrag te ontwikkel. Die raamwerk bestaan uit die volgende ses interafhanklike afdelings: • Strategie en visie: Doelwitte vir kennisoordrag moet belyn wees met die besigheidstrategie en moet gekommunikeer word deur middel van ‘n aangrypende kennisoordrag visie. • Kultuur: ‘n Kultuur wat kennisdeling onderskraag word benodig om ‘n kennisoordrag-program suksesvol te implementeer. Kultuur skep ook die konteks vir sosiale interaksie wat integrasie van die verskillende besighede aanhelp na ‘n oorname. • Bestuur van verandering: Die bestuur van verandering is onontbeerlik om die agtergrond, metodiek en moontlike voordele van kennisoordrag-programme effektief te kommunikeer. • Kennisoordrag hulpbronne: Kennisoordrag hulpbronne word benodig om die kennisoordrag aktiwiteite uit te voer. Die optimale gebruik van hierdie hulpbronne is noodsaaklik om operasionele voortreflikheid te verseker. • Kennisoordrag prosesse: Die kennisoordrag prosesse dui aan hoe kennis oorgedra sal word en is van kritiese belang vir die fasilitering, stimulasie, meting en versterking van kennisoordrag. Daar is ses stappe geïdentifiseer in die proses, naamlik identifisering, prioritisering en “benchmarking” van sleutel besigheidsdrywers, ‘n analise van die gapings, identifisering van aksies wat die gapings kan uitwis en monitering van inisiatiewe. vii • Kennisoordrag stelsels: ‘n Versameling gereedskapstukke, tegnieke en ondersteunende infrastruktuur word benodig om die kennisoordrag-prosesse te ondersteun. Alhoewel die stelsels die prosesse onderskraag kan dit kennisoordrag nie in isolasie laat plaasvind nie. Die raamwerk illustreer dat kennisoordrag binne en tussen organisasies afhanklik is van veel meer as net die interaksie tussen die houers en ontvangers van kennis. ‘n Formele, sistematiese benadering word benodig om maksimum waarde te ontsluit. Die konseptuele raamwerk wat in hierdie studie ontwikkel is verskaf hierdie benadering, en is doelgerig vir die gebruik en konteks binne die Exxaro Sands Kommoditeit Besigheid. ‘n Gestruktureerde implementeringsproses word benodig om te verseker dat die doelwitte, riglyne en mylpale vir effektiewe kennisoordrag bereik word.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaf 71. / by David Mark Ryter. / B.S.

Today bike sharing systems exists in many cities around the globe after a recent growth and popularity in the last decades. It is attractive for cities and users who wants to promote healthier lifestyles; to reduce air pollution and gas emission as well as improve traffic. One major challenge to docked bike sharing system is redistributing bikes and balancing dock stations. There are studies that propose models that can help forecasting bike usage; strategies for rebalancing bike distribution; establish patterns or how to identify patterns. Some of these studies proposes to extend the approach by including weather data. Some had limitations and did not include weather data. This study aims to extend upon these proposals and opportunities to explore on how and in what magnitude weather impacts bike usage. Bike usage data and weather data are gathered for the city of Washington D.C. and are analyzed by using a clustering algorithm called k-means. K-means is suitable for discovering patterns within the data by grouping (clustering) similar instances, which literature review also advocated. In this project, the k-means algorithm managed to identify three clusters that corresponds to bike usage depending on weather. The results show that weather impact on bike usage was noticeable between clusters. It showed that temperature followed by precipitation weighted the most, out of five weather variables. Results also supported that the use of k-means was appropriate for this type of study.

Sistemas de Bicicletas Compartilhadas (SBCs) têm sido implantados e aprimorados nos últimos anos nas principais cidades do mundo. Neste tipo de sistema, usuários podem retirar e devolver bicicletas em qualquer estação da rede, desde que haja bicicleta e vaga disponível, respectivamente. Porém, devido às características de ocupação do solo em grandes centros urbanos, existe uma tendência natural de desbalanceamento nos fluxos dos usuários, fazendo com que em determinados horários certas estações fiquem lotadas de bicicletas enquanto outras estações estão vazias. Para mitigar este problema, gestores de SBCs utilizam veículos de carga para rebalancear o sistema (reposicionar as bicicletas entre as estações). Entretanto, usualmente, esse processo na prática não é realizado com auxílio de ferramentas quantitativas que tornem o processo racional ou maximizem sua eficácia. Nesse sentido, no presente trabalho é proposto um modelo híbrido de simulação com otimização, aplicado ao rebalanceamento de um SBC brasileiro e com potencial para utilização em sistemas reais com o objetivo de melhorar seus níveis de serviço. Além disso, apresenta-se uma análise de dados e a caracterização de uso deste SBC, um histórico de evolução de SBCs ao redor do mundo e sua bibliografia pertinente, a fim de registrá-los na literatura e de se obter maior compreensão deste tipo de sistema. / Bike Sharing Systems (BSSs) have been implemented and enhanced in several major cities around the world, during the past few years. In such systems, users can take off a bike and return it at any network\'s station, provided that there is a bike and a dock available, respectively. However, these systems face an operational problem, caused by the fact that users\' flows are not balanced, bringing on that, at some point in time, some stations will be completely full while others will be empty. To tackle this issue, cargo vehicles are used by BSS\'s operators to rebalance the system (relocate bicycles through the stations). However, in most cases this process is not supported by quantitative tools that make the process rational or maximize its effectiveness. In this sense, this work proposes a hybrid model of simulation with optimization, applied to the rebalance of a Brazilian BSS and with potential for use in real systems with the aim of improving their service levels. In addition, is presented a data analysis and a usage study of this specific BSS, a BSSs evolutionary study and its relevant literature with the purpose of registering them in the literature and achieving a superior understanding of the problem.

Advances in communications technologies entail demands for higher data rates. One of the popular solutions to fulfill this requirement was to allocate additional bandwidth, which unfortunately is not anymore viable due to spectrum scarcity. In addition, spectrum measurements around the globe have revealed the fact that the available spectrum is under-utilized. One of the most remarkable solutions to cope with the under-utilization of radio-frequency (RF) spectrum is the concept of cognitive radio (CR) with spectrum sharing features, also referred to as spectrum sharing systems. In CR systems, the main implementation issue is spectrum sensing because of the uncertainties in propagation channel, hidden primary user (PU) problem, sensing duration and security issues. Hence, the accuracy and reliability of the spectrum sensing information may inherently be suspicious and questionable. Due to the imprecise spectrum sensing information, this dissertation investigates the performance of an orthogonal frequency-division multiplexing (OFDM)-based CR spectrum sharing communication system that assumes random allocation and absence of the PU's channel occupation information, i.e., no spectrum sensing is employed to acquire information about the availability of unused subcarriers or the PU's activity. In addition, no cooperation occurs between the transmitters of the PUs and secondary users (SUs). The main benefit of random subcarrier utilization is to uniformly distribute the amount of SUs' interference among the PUs' subcarriers, which can be termed as interference spreading. The analysis and performance of such a communication set-up provides useful insights and can be utilized as a valid benchmark for performance comparison studies in CR spectrum sharing systems that assume the availability of spectrum sensing information. In the first part this dissertation, due to the lack of information about PUs' activities, the SU randomly allocates the subcarriers of the primary network and collide with the PUs' subcarriers with a certain probability. The average capacity of SU with subcarrier collisions is employed as performance measure to investigate the proposed random allocation scheme for both general and Rayleigh channel fading models. In the presence of multiple SUs, the multiuser diversity gain of SUs is also investigated. To avoid the subcarrier collisions at the SUs due to the random allocation scheme and to obtain the maximum sum rate for SUs based on the available subcarriers, an efficient centralized sequential algorithm based on the opportunistic scheduling and random allocation (utilization) methods is proposed to ensure the orthogonality of assigned subcarriers. In the second part of this dissertation, in addition to the collisions between the SUs and PUs, the inter-cell collisions among the subcarriers of SUs (belonging to different cells) are assumed to occur due to the inherent nature of random access scheme. A stochastic analysis of the number of subcarrier collisions between the SUs' and PU's subcarriers assuming fixed and random number of subcarriers requirements for each user is conducted. The performance of the random scheme in terms of capacity and capacity (rate) loss caused by the subcarrier collisions is investigated by assuming an interference power constraint at PU to protect its operation. Lastly, a theoretical channel fading model, termed hyper fading channel model, that is suitable to the dynamic nature of CR channel is proposed and analyzed. To perform a general analysis, the achievable average capacity of CR spectrum sharing systems over the proposed dynamic fading environments is studied.

Sistemas de Bicicletas Compartilhadas (SBCs) têm sido implantados e aprimorados nos últimos anos nas principais cidades do mundo. Neste tipo de sistema, usuários podem retirar e devolver bicicletas em qualquer estação da rede, desde que haja bicicleta e vaga disponível, respectivamente. Porém, devido às características de ocupação do solo em grandes centros urbanos, existe uma tendência natural de desbalanceamento nos fluxos dos usuários, fazendo com que em determinados horários certas estações fiquem lotadas de bicicletas enquanto outras estações estão vazias. Para mitigar este problema, gestores de SBCs utilizam veículos de carga para rebalancear o sistema (reposicionar as bicicletas entre as estações). Entretanto, usualmente, esse processo na prática não é realizado com auxílio de ferramentas quantitativas que tornem o processo racional ou maximizem sua eficácia. Nesse sentido, no presente trabalho é proposto um modelo híbrido de simulação com otimização, aplicado ao rebalanceamento de um SBC brasileiro e com potencial para utilização em sistemas reais com o objetivo de melhorar seus níveis de serviço. Além disso, apresenta-se uma análise de dados e a caracterização de uso deste SBC, um histórico de evolução de SBCs ao redor do mundo e sua bibliografia pertinente, a fim de registrá-los na literatura e de se obter maior compreensão deste tipo de sistema. / Bike Sharing Systems (BSSs) have been implemented and enhanced in several major cities around the world, during the past few years. In such systems, users can take off a bike and return it at any network\'s station, provided that there is a bike and a dock available, respectively. However, these systems face an operational problem, caused by the fact that users\' flows are not balanced, bringing on that, at some point in time, some stations will be completely full while others will be empty. To tackle this issue, cargo vehicles are used by BSS\'s operators to rebalance the system (relocate bicycles through the stations). However, in most cases this process is not supported by quantitative tools that make the process rational or maximize its effectiveness. In this sense, this work proposes a hybrid model of simulation with optimization, applied to the rebalance of a Brazilian BSS and with potential for use in real systems with the aim of improving their service levels. In addition, is presented a data analysis and a usage study of this specific BSS, a BSSs evolutionary study and its relevant literature with the purpose of registering them in the literature and achieving a superior understanding of the problem.