Dissertations / Theses on the topic 'Poor access'

As a result of increasing college costs and diminishing organizational support, poor and ethnic-minority students are finding it increasingly difficult to attend large public research universities. To investigate the potential relationship that exists between market-oriented practices in higher education and access for poor and ethnic-minority students, the Institutional Logics Perspective is employed as a theoretical frame to contextualize the precursors, content, and consequences of the market logic in the public higher education system. Hypotheses drawing out linkages between the mechanisms of the market logic and decreased student access are offered. A fixed-effect model is then constructed to evaluate proposed connections between university practices undergirded by the logic and access for both poor and ethnic-minority student populations. Results are discussed and the ramifications of the market logic for the future of accessible public higher education are explored in the context of social justice.
Ph. D.

Thesis (MDF (Business Management))--University of Stellenbosch, 2009.
AFRIKAANSE OPSOMMING: Die langtermynversekeringsindustrie het voorheen slegs finansiële produkte en dienste ontwerp, wat gefokus was op die middel tot hoër inkomstegroepe. Die armes was dus uitgesluit, primêr as gevolg van die laer inkomstegroepe wat nie lewensversekeringsprodukte kon bekostig nie. Inteendeel, arm huishoudings is, en was, meer kwesbaar vanweë die feit dat hulle geredelik blootgestel word aan meer diverse risiko’s – mensgemaakte, sowel as natuurlike risiko’s - terwyl hulle juis diegene is wat minder middele het om dit bestuur. Hierdie toedrag van sake het egter drasties verander gedurende die afgelope paar jaar. Die onderskeie partye, insluitend verteenwoordigers van die langtermynversekeringsindustrie, het konsensus bereik ten opsigte van die ontwikkeling van die Finansiële Sektor Handves wat in ooreenstemming is met die nasionale swart ekonomiese bemagtigingstrategie. Die oogmerk van die Finansiële Sektor Handves was nie net om mense in die laer inkomstegroepe te bemagtig nie. Dit het ook ten doel om finansiële insluiting te verseker, en mettertyd, die aktiewe deelname van die armes in die hoofstroom van die Suid-Afrikaanse ekonomie. ’n Stel toegangstandaarde was gevolglik ontwikkel en geïmplementeer, wat die langtermynversekerings-produkaanbiedinge aan LSM 1-5 reguleer (met ander woorde vir die doeleindes van hierdie verslag, huishoudings wat minder as R3 000 per maand verdien). Die doel van die standaarde wat ontleed word in hierdie verslag, is om te verseker dat die langtermynversekeringsindustrie geskikte produkte ontwerp wat die minimum standaarde soos beskryf in die Finansiële Sektor Handves, nakom. In beginsel word die toepaslikheid en geskiktheid van die toegangstandaarde in hierdie verslag geëvalueer, met die oogmerk om te bepaal wat die standaarde inhou vir beide die verbruiker asook die lewensversekeraar van ’n verslaggewingsperspektief. Die eerste deel van die toegangstandaarde wat goedgekeur is deur die Finansiële Sektor Handves in 2007, het slegs begrafnisdekking ingesluit, terwyl die tweede deel gefokus het op nie-begafnisprodukte en sedert 2008 geïmplementeer is. Laasgenoemde het die volgende dekking ingesluit: lewensversekering, dekking vir fisiese ongeskiktheid, kredietlewensversekering en gewone lewensversekering. Die toegangstandaarde wat van toepassing is op verbandlenings is egter nog nie gefinaliseer nie en is gevolglik nie ingesluit in hierdie verslag nie. ’n Fundamentele vraag ten opsigte van die daarstelling van toegangsprodukte vir die laer inkomstegroepe, is wat die rol is van die publiek vergeleke met die privaatsektor en dié van die regering. Terwyl die regering optree as die wetgewer, moet dit ook daarteen waak om nie te veel van ’n rigiede proses vir die privaatsektor daar te stel nie. Die wetgewer moet die relevante reëls en regulasies stipuleer en sekerheid verskaf ten opsigte van die inhoud daarvan. Terselfdetyd moet die wetgewer ook die privaatsektor asook `n klimaat van innovasie ondersteun, sowel as die daarstelling van ’n stabiele regulerende atmosfeer. Behalwe die ontwikkeling van geskikte, bekostigbare en minder komplekse produkte, berus die verantwoordelikheid op die privaatsektor om vertroue te skep in die langtermynversekerings-industrie asook om die noodsaaklikheid van risiko-dekking te propageer. Versekeraars het verder nodig om die laer inkomstegroepe as ’n winsgewende segment te beskou, terwyl die armes versekering as ’n noodsaaklike vereiste moet beskou. Hoe meer vertroue geskep word deur die versekeringsindustrie, hoe minder sal mense in die laer inkomstegroepe hul geld belê in die informele sektor wat gekenmerk word deur die afwesigheid van regulering, minder sekuriteit en hoër risikos. Dit is verder noodsaaklik vir die sukses van die verskaffing van toegang tot finansiële produkte, om in gedagte te hou watter impak dit op die verbuiker sal hê. Met betrekking tot die produkte wat ontwikkel en bemark word deur die lewensversekeringsindustrie: spreek dit werklik die behoeftes van die laer inkomstegroepe aan en dra dit positief by tot transformasie? Die privaatsektor is as gevolg daarvan grotendeels afhanklik van marknavorsing en analises oor verbuikerstendense gemeet oor tyd. Die impak wat finansiële produkaanbiedinge het op die laer inkomstegroepe, kan gevolglik nie onafhanklik beskou word nie want die behoeftes, verwagtinge en profiel van die onderste deel van die piramide sal met verloop van tyd verander. Mededinging dra as sulks ook positief by tot die daarstelling van toegang tot finansiële produkte en dienste. Dit dwing die privaatsektor (die lewensversekeringsmaatskappye) om vorendag te kom met innoverende wyses om effektiewe toegangsprodukte en dienste te kan lewer aan die armes. Die bring mee dat die verbruiker waarde vir geld kry wanneer finansiële produkte en dienste aangekoop word van lewensversekeraars. Met verwysing na die toepaslikheid van die langtermynversekeringsindustrie se toegangstandaarde en of dit die behoeftes van die armes bevredig: die lewensversekeringsindustrie het inderdaad baie bereik gedurende die afgelope paar jaar, deurdat konstruktiewe geleenthede geskep is vir die laer inkomstemark. Gegewe die minimum-vereistes soos uiteengesit in die Finansiële Sektor Handves, kan die armes nou ook langtermynversekeringsprodukte bekom wat uitdagings soos fisiese beskikbaarheid, toegang tot transaksies, bekostigbaarheid, diskriminasie en kompleksitiet aanspreek. Dit is daarom noodsaaklik vir die doeleindes van effektiewe finansiële insluiting, om vir verbruikersopleiding ook voorsiening te kan maak. Finansiële geletterdheid sal in beginsel die laer inkomstegroepe in staat stel om hulself te kan bemagtig en terselfdertyd die teikengroep in staat stel om meer ingeligte besluite te kan neem ten opsigte van hul finansies. Laasgenoemde kan egter nie in isolasie geskied nie. Finansiële geletterheid en dus verbruikersopleiding, is minstens net so belangrik. Dit is juis daarom dat, bo en behalwe die regering wat die rol as wetgewer vertolk deur die toepassing van die reg, al die betrokke partye veronderstel is om ’n gemeenskaplike oogmerk te hê. Met ander woorde, dit verwys direk na transformasie en die doelwit om mense in die laer inkomstegroepe te bemagtig – nie net om finansiële insluiting te bewerkstelling nie, maar van meer belang, om te verseker dat die armes oor die vermoë beskik om meer ingeligte besluite te kan neem oor hul finansies. Hierdie aspek sal veral bydra tot effektiewe toegang tot finansële dienste in die ware sin van die woord - as die armes ’toegelaat’ word om meer aktief deel te kan vorm van die hoofstroom van die land se ekonomie.
ENGLISH ABSTRACT: Previously, the long-term insurance industry only developed financial products and services that were mainly targeted at the middle to high income groups. The poor have thus been excluded, primarily due to them not being able to afford financial products and services offered by life insurers. However, poor households are, and have been, more vulnerable because they are often exposed to more diverse risks, both ‘man- made’ and natural, whilst having fewer instruments to manage them. This state of affairs has drastically changed during the past couple of years. The respective stakeholders, including representatives from the long-term insurance industry, reached consensus with regards to the development of the Financial Sector Charter which is aligned to the national black economic empowerment strategy. The objective of the Financial Sector Charter is not only to empower people in the lower income groups. It also aims to ensure financial inclusion and, eventually, the active participation of the poor in the mainstream of the South African economy. A set of access standards that governs life insurance products and services offered to LSM 1-5 (i.e. for the purposes of this report, households earning less than R3 000 per month), were developed and implemented accordingly. The objective of the access standards, analysed in this report, is to ensure that the long term insurance industry develops appropriate products that meet the minimum standards defined in the Charter. In principle, this report evaluates the feasibility of the access standards with the aim of ascertaining what the standards imply for both the consumer as well as the life insurer from a reporting perspective. The first set of access standards, approved by the Financial Sector Charter in 2007, included funeral products only, whereas the second phase, which focused on nonfuneral products, came into effect in 2008. The latter is applicable to the following financial products: life cover, physical impairment cover and credit life cover. The access products standards relevant to mortgage protection are not yet finalised and have therefore been excluded from this report. A fundamental question in terms of providing access to the low income groups is the role of the public versus private sector delivery as well as that of government. Whilst government acts as the lawmaker, it also needs to be sensitive towards not creating too much ‘red tape’ for the private sector to comply with. The regulator should therefore stipulate and clarify the relevant rules and regulations, but at the same time support the private sector and encourage a climate of innovation as well as creating a stable regulatory environment. Apart from developing appropriate, affordable and less complex insurance products, the private sector’s responsibility is to create trust in the insurance industry as well as to promote the need for risk insurance. Insurers thus need to see low income earners as a profitable segment, whereas poor people need to see insurance as a necessity. The more trust is created by the insurance sector, fewer people in the low income groups will invest their money in the informal sector which entails no regulation, less security and higher risks. It is furthermore pivotal for the success of access to financial services to take into account how this will impact on the consumer. With respect to the products developed and marketed by the life insurance industry: does it really meet the needs of the poor and does it contribute positively to transformation? The private sector is therefore heavily dependent on research and analyses of consumer trends measured over time. As a result, the impact that financial product offerings have on the low income earners cannot be dealt with on its own, because as time passes so will the needs, expectations and profile of the bottom of the pyramid change. On its own, competition tends to also contribute positively towards access to financial services. It forces the private sector (i.e. life insurance companies) to come up with innovative ways of providing effective access, products and services to the poor. This ensures that the end user gets value for money, when procuring financial products and /or services from life insurers. In respect of the viability of the long-term insurance industry’s access standards and whether or not it speaks to the needs of the poor: the life industry has indeed achieved a lot over the past couple of years, by creating constructive opportunities for the lower end of the market. Given the minimum requirements as per the Financial Sector Charter, poor people can now also obtain long-term insurance products that address challenges with regards to physical accessibility, transactional access, affordability, non-discrimination and the level of complexity. However, more important for the low income group to participate effectively in the mainstream of the South African economy, is the fact that the need for financial literacy is even bigger. It is one thing to have the right of entry (i.e. access) to the financial services sector in terms of life insurance product offerings, but it is different if that same target audience does not have the ‘know-how’ to use and implement the products developed. It is hence an imperative for the purposes of effective financial inclusion to also make provision for consumer education. In principle, financial literacy will enable the lower income groups to become more empowered and at the same time, ensure that the target audience is equipped to make more informed decisions about the finances. Given the latter, it can however not happen in isolation. Financial literacy and thus consumer education, is equally important - if not more. It is therefore critical that, apart from government fulfilling its role as regulator by upholding the rule of law, all the stakeholders should have a universal goal. In other words, this directly addresses transformation and the objective of empowering people in the lower income groups – i.e. not only to ensure financial inclusion, but more importantly to enable poor people to make more informed decisions about their finances. And only this will contribute to effective transformation in the true sense of the word - if poor people are ‘allowed’ to become more actively involved in the mainstream of the South African economy.

Access to electricity is an important precondition to many aspects of human and economic development. Yet, in rural sub-Saharan Africa in particular, access rates remain very low — at an average of 17% and much lower in some cases. Rural electrification in Kenya, the focus of this thesis, had only reached 7% in 2014. Given the goal of universal electrification by 2030, formulated as part of Sustainable Development Goal 7, scalable and replicable approaches that are able to support productive and non-productive uses are required. Mini-grids are one promising solution to this problem, alongside grid extension and off-grid approaches such as solar home systems. However, their long-term operational sustainability has historically been a challenge. While the academic literature to date on sustainable energy access has largely been two-dimensional in its analysis of mini-grids (focusing on technology and economics or financing), this thesis contributes to an emerging body of recent contributions to the literature, which have begun to foreground socio-cultural considerations. Bridging the literature on collective action for common-pool resource (CPR) management and property rights theory, a refined theoretical framework is produced for the purpose of analysing the institutional conditions for sustainable management of rural mini-grids. The utility of this framework and of treating electricity in a mini-grid as a CPR is demonstrated via empirical analysis of three case studies of mini-grids in rural Kenya and evidence from 24 expert interviews. This yields insights on nontechnological approaches to addressing operational challenges relating to sustainable mini-grid management, e.g. fair allocation of limited amounts of electricity to different consumers in ways that are acceptable to the entire community. This thesis develops contributions to the literature on sustainable CPR management and collective action, property rights theory and energy access in developing countries. From these theoretical and empirical insights, it explores a novel institutional structure for sustainable management of pro-poor mini-grids in the form of a community–private property hybrid management platform, thereby opening up opportunities for future research into the implementation of such a platform. The thesis represents the first comprehensive attempt to analyse the institutional aspects of pro-poor mini-grid management as well as the first comprehensive attempt to treat electricity in a mini-grid as a CPR.

Microfinance has gained prominence as a policy option for addressing poverty. Although microfinance has a long history, its growing appeal is usually associated with the attention given to the Grameen Bank of Bangladesh, which pioneered group-based lending to poor women. Following the ‘successes of Grameen and the promotion of ‘cloned’ institutions, advocacy for microfinance has focussed primarily on microcredit. Consequently, microfinance as savings, insurance, and other forms of financial intermediation received far less attention. It was believed that microcredit was a more reliable and faster means to achieve poverty reduction, especially through supporting the entrepreneurialism of the poor. Microcredit then became a mantra of the microfinance sector, increasingly identified as its ‘raison d’être’ and the justification for the investment of billions for dollars. This thesis focuses on the relationship between microfinance and poverty. It puts savings at the centre of the research through an analysis of a savings-led financial services co-operative known as the ‘Village Banks’ in South Africa. The research considers the asserted link between microfinance and poverty from both a theoretical and empirical interrogation. It questions the limited engagement that the microfinance literature has had with the various theories on poverty and attempts to formulate a more nuanced understanding of relations between the two. The empirical contribution is a mixed method of qualitative analysis, in the form of focus groups held in four different Village Bank communities, and quantitative analysis from an original panel of households in one community. The thesis argues that a savings-led model of microfinance has the ability to contribute to the challenges of poverty reduction more than is currently acknowledged. It will also argue that, when provided with the necessary support, member-owned financial institutions, such as the Village Banks, offer a potential solution to addressing the inherent challenges of providing low-cost banking services in rural areas.

According to the Federal Ministry for Economic Cooperation and Development (2012-2013), access to higher education is limited in most of the developing countries due to inadequate budgets and lack of schools and teaching staff. The use of educational technology could help bridge the gap, but research has only explored the use of available technologies to enhance learning where higher education is already accessible. The purpose of this case study was to investigate the use of one-to-many videoconferencing as an education access tool for high school seniors seeking higher education in the most devastated areas of Haiti. The theoretical framework for this study is based on Bandura's social learning theory, activity theory, and constructivist epistemology. This study attempts to explore the feasibility of using one-to-many videoconferencing learning to enhance access to education in Haiti. The study also analyzes the experiences of various sets of participants. The data were drawn from 13 interviews involving the school principal, the school's technology expert, 10 students, and one instructor corroborated by hours spent observing the same participants engaged in classroom activities via videoconferencing. The participants were interviewed on their experiences with the new delivery method proposed and utilized in the study. The data from this study suggest that by preserving the features of the familiar classroom model, videoconferencing could be successfully utilized to compensate for the lack of other facilities for higher education. The data was coded and analyzed using the NVivo data analysis software. The study will allow Haitian professionals living outside of the country to affect change in access to higher learning in Haiti.

The premise of the thesis is that the developmental use of urban land should be ethical, fair and promote social justice. Using multiple research approaches and mixed methods this thesis examines the urban land question in South Africa and particularly Cape Town where land distribution and ownership are inequitable. The thesis unpacks land redistribution, land tenure reform and land restitution within this context. It is argued that the South African Constitution commits government to protect the property rights of those who currently own property and at the same time redistribute land to those who have been dispossessed and explores what this tension means for urban land redistribution and reform using the freedoms approach developed by Amartya Sen as a conceptual framework and as alternative to the neo-classical model. The main findings of the thesis can be summarized as follows. a) The thesis demonstrates that there is no logical reason why the freedoms approach cannot be extended to include urban land. b) The entitlements and endowments that urban land could bestow on the urban poor are shaped by how the State invests in land through the instruments of land planning and land use management which call for a significant role for the State as custodian of public land to not only make explicit the land asset register under public ownership but also instill trust in the poorer sectors of urban society. c) A two track system of land planning and land use management may be more appropriate in the post apartheid South African city, one stream for market driven land and one for targeted public land programmes that directly address urban poverty provided that the State is able to make strong connections between the philosophical and the technical aspects of land and land use management systems. d) As a two track system is suggested the land use management system requires to be reframed. To facilitate land redistribution and reform in urban areas of South Africa therefore, the thesis suggests that a deliberative and systemic planning approach needs to be adopted that is intervention focused. Only when the State assumes a more critical interventionist role in public land programmes would it be possible to obtain social justice and the principles of the good city in the South African urban context. e) Gaining access to and control over land resources beyond the market is possible but limiting for the majority of the urban poor when land and housing debates are conflated. This conflation results in other land debates being silenced yet these have the potential to offer alternatives to the neo-classical model of land and land use management as well as promote a wider role for public land than just housing.

Includes bibliographical references (leaves 105-111).
Since the early 1980's, a number of countries have been undertaking power sector reform. Very often the drivers for change included the need to reduce reliance on public finances and to obtain foreign capital, either to service loans, or for investing in new capacity. Latin American countries were the forerunners in this regard, with Chile amongst the first. The other main driver was to improve the financial and technical performance of the electricity industry. The rationale for this initiative could also be found in other factors, which are discussed as the countries are dealt with individually later in this document. One important aspect thereof is clearly the 'public benefit' implications of power sector reform, which are more pressing in developing countries. Until the 1980's, the electricity industry was viewed as a natural monopoly, and the concept of economies of scale reinforced this point of view. However, with dramatic technology improvements, it became possible to generate electricity competitively in smaller power plants, and thus alternatives to monopolistic industries were increasingly feasible. Competition is now possible in generation and supply. Developers other than the state can participate in the industry either as Independent Power Producers (IPPs) or as distributors and suppliers of electricity. According to the principle of competition, the introduction of new players into the market should lower electricity prices. This study investigates if this holds true in developing countries and whether power sector reform slows down or accelerates electrification access for the poor.

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Affordability is a key concern of international donors who finance antiretroviral drugs to treat AIDS in Sub-Saharan African countries. The ability of Sub-Saharan Africa to reduce their prices below large-scale manufacturers in India is challenging. Additionally, these medicines must meet The World Health Organization prequalification standards. While the cost of second-line ARVs remains a concern, donors should also focus resources on other factors of ARV access, such as the supply of human resources for health, infrastructure and issues of sustainable financing. This research specifically aims to determine if the domestic production of
antiretroviral drugs can be a successful and viable option to increase access to ARVs in sub-Saharan Africa by using three case studies of Uganda, Kenya and The democratic Republic of Congo. The research is intended to explore a potentially economical way to provide ARVs to populations with HIV/AIDS in order to move away from a dependence on foreign aid, which does not guarantee continued long-term access to the medications. Since ARVs must be taken daily for the duration of the patient's life, it is important to develop ways to increase access to the medications in a manner that facilitates the long-term drug procurement. The success of local manufacturers then relies on the capacity of the firm to achieve two necessary elements of donor-financed requirements: international quality standards and economies of scale to lower price. I recommend that more countries in Africa should produce ARVs locally in order to lower to cost and increase accessibility, especially in small villages. Even though the current operation of local production has not led to a significant increase in access primarily due to market entry restrictions, this endeavor have the ability to amplify long-term access to affordable ARV drugs

The South African law and legal system can and should be a mechanism through which the lives of all resident there are enhanced through the safeguarding and advancement of the fundamental rights guaranteed in its Bill of Rights. This thesis focuses on ‘legal aid’ service delivery (broadly speaking) for the indigent in a particular locality by and through registered law clinics, other legal services providers and via other means in civil rather than criminal matters. In this regard there continue to be very substantial differences between the proper access to civil justice requirements of constitutional South Africa and the actual situation which has existed since the dawn of South Africa’s democratic era which continues unabated. Justice and equality are promised to all in South Africa, yet due to gaps in the ‘net’ of free legal services provided to the indigent, the ability to pay for legal services in civil cases often remains the deciding factor. This study examines the constitutional obligations which, it is argued, apply to the provision of free civil legal services to impoverished people in South Africa. This research considers the law as a vector for necessary positive transformation in the daily lives of those resident in South Africa, which is considered within the country’s woefully unequal socio-economic situation. It builds upon existing research and court authority which show the function of access to justice as an important promoter of the type of society envisaged by the South African Constitution - one where the enjoyment of justice and equality are within the reach of all. However, at present, if one can afford the expensive services of lawyers in civil matters, then access to justice is far more readily attainable. But the opposite is true where someone is denied meaningful access to justice through a lack of legal representation because they cannot afford prohibitively high lawyers’ costs (and disbursements) and no adequate alternatives are provided for by the state or through other means. In these circumstances a vulnerable, unrepresented litigant in a civil case faces a greatly increased likelihood of being denied proper access to a daunting and intricate legal system. There are two main reasons for concentrating on free legal services to the ‘needy’ in civil rather than criminal matters. In the first place, all available statistics show that a huge proportion of legal aid services in South Africa has been and continues to be dispensed in criminal rather than civil cases. Secondly, there has been minimal research or case authority in South Africa on legal aid and other free legal services for impoverished people in civil matters. This thesis examines the state of free civil legal service provision and the need for such assistance within the eThekwini Metropolitan Municipality, one of South Africa’s largest metropoles. This analysis includes an empirical study of the requests for free civil legal services in a particular year by qualifying potential clients in eThekwini and the degree to which free legal service providers are meeting or failing to meet those needs. The study considers the legal service provision in such matters by legal non-governmental organisations, state-supported legal service providers and the work of legal professionals in private practice acting pro bono. The thesis then proposes a model for eThekwini for coordinating (and concurrently improving) civil legal aid services, pro bono legal work and other forms of free legal assistance - like community service by senior law students and law graduates - in response to the particular needs and circumstances facing the indigent there. When referring to the concept of ‘legal aid services’, this research concentrates on legal advice, assistance and representation to indigent clients. However, the promotion of legal rights awareness to such clients is often necessary to open their eyes to the possibility of legal avenues, where appropriate, to improve their situations. Therefore this study also considers - albeit to a lesser degree - this more indirect form of legal assistance through the dissemination of legal knowledge in an accessible form to clients who would qualify for legal aid assistance. The work concludes by briefly postulating the likely appropriateness (and/or limitations) of the aforementioned ‘free civil legal service model for the indigent’ beyond eThekwini.

Water is life. While access to water supply and sanitation facilities is considered as one of the most basic human needs, it is also today considered as a human right. Lack of access to safe, affordable, close and adequate water supply and sanitation facilities remains one of the leading causes of diseases and deaths in the world. There are many reasons for this unacceptable situation. One key characteristic is the inadequate institutional and legal framework for water supply and sanitation provision in place. The aim of this research is to gain an improved understanding of existing frameworks, to see what and how it makes the links between the local, regional, national and international levels for communities to access improved water supply and sanitation facilities. The hypothesis being that a framework which does not provide these linkages can have a negative impact on water supply and sanitation provision for poor communities. The research focuses on the institutional and legal frameworks relating to the Senegal and Volta river basins, in West Africa and their constituent countries, one of which, Ghana, is the focus of a more detailed analysis. The study identified that insufficient attention has been given to the establishment of an overall institutional and legal framework at all levels, and particularly to the establishment of regulatory and enforcement bodies at the local, regional, national and international levels and their inclusion in the formulation of water supply and sanitation policies at all levels. A model institutional and legal framework has been developed as a benchmark against which existing frameworks can be evaluated. It draws out key features extending from the local to the international level. The research argues that governments have a primary role to play in facilitating the provision of water supply and sanitation facilities to communities, in particular the poor.

This study seeks to provide information relevant to public policy that will lead to increased access and utilization among this vulnerable population and to reinforce the validity of the behavioral model for vulnerable populations. This study is a secondary analysis of data collected in a study that examined adult, working-aged patients within the John Peter Smith Health Network, which is a large, urban, tax supported county health care system in Fort Worth, Texas. From a sampling frame of 10,000 patients, the study analyzed data for 243 low-income, white, working-age males, collected from computer assisted telephone interviews in 2000. Cross-tabulations and bivariate logistic regressions were used to analyze the effect of 8 independent variables (age, marital status, insurance, employment status, a usual source of care, competing needs, experiences with paperwork, and perceived health status upon 5 dependent variables pertaining to unmet health care, unmet prescription medicine needs, unmet dental needs, utilization of doctors in emergency departments, and overnight hospital stays. The results show the safety net system is failing to meet the needs of this vulnerable population. The findings indicate white men who found it necessary to forgo health care due to other needs were almost five (4.973) times as likely as those who did not find it necessary to forgo care due to other needs, to report having a problem getting the health care that they need (p = ≤ .001). The odds of having a problem getting needed dental care are about 66% lower for white men who have private insurance through work compared to those who do not have private insurance through work (p ≤ .05).

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management, 2006.
Includes bibliographical references (p. 57-59).
Donor grants and soft loans have been utilized by many microfinance institutions (MFIs) to support their operations. However, such grants and loans, already of limited size and availability, are becoming harder to access as the pool of global MFIs grows. Another option for MFIs is tapping international capital markets, international loan and security markets, but there are many barriers to this practice. This paper studies how MFIs and the poor who are seeking capital to foster their entrepreneurial spirits can overcome these barriers to access international capital markets and meet the growing micro finance demand. First, this paper establishes the degree of linkage between MFIs and international financial markets by reviewing the present funding condition of MFIs. It concludes that purely commercially based funding from capital markets is minimal except for some of the best managed MFIs. A huge gap exists between most other MFIs and international capital markets. Second, this palper studies the microfinance investment potential by analyzing the returns of one microfinance investment fund. It concludes that the profile of microfinance investment matches the needs of investors in capital markets.
(cont.) Investors in developed countries are always looking for investment products that mitigate their portfolio volatility. This paper verifies that microfinance has an attractive profile matching these needs, and offering stable return, as well as low correlation with stocks, bonds and macroeconomic factors. Capital market investors and microfinance have the potential to build win-win relationships. One of the remaining challenges of MFIs is generating required return commensurate with risks. Third, this paper proposes securitization in a microfinance global pool as a means to overcome the barriers to connecting MFIs and the poor to capital markets. In this securitization scheme, the global pool buys microcredits from MFIs, thereby 1) increasing return, 2) enabling many MFIs to obtain funds from capital markets by sharing fixed costs of funding, 3) reducing exchange rate and geographic concentration risks, and 4) creating secondary markets and liquidity. Some challenges to securitization still need to be overcome. Nevertheless, this paper demonstrates that; securitization in the microfinance global pool will be an effective means to bridge the gap between capital markets and MFIs and the poor.
by Daisuke Ueno.
M.B.A.

As the case with most countries across Latin America, unprecedented migration to urban areas has strained city infrastructure systems. More particularly, the region faces a pressing crisis of water security, where rapid urbanization has outpaced water sector development. This thesis addresses the water infrastructure reform in El Alto and La Paz, Bolivia, focusing on strategies to better promote water access for the peri-urban poor. The research investigates the level of progressivity of water service expansion and pricing regimes: in other words, does the present model of water distribution positively improve the lives of the poorest groups? By investigating these social dimensions of water management, this study brings perspectives on the broader dialogue on Bolivia’s economic development, along with issues of participatory governance. Resumen: Como es el caso en muchos países latinoamericanos, la migración a áreas urbanas a niveles sin precedentes ha superado la capacidad de infraestructura. Concretamente, la región se enfrenta a una urgente crisis en la seguridad de agua potable dado que la rápida urbanización ha sobrepasado el desarrollo de este sector. Esta tesis aborda la reforma de la infraestructura de agua potable en El Alto y La Paz, Bolivia, enfocando en las estrategias para mejorar el acceso a agua por parte de los residentes periurbanos pobres. La investigación averigua el nivel de progresividad de los regímenes de precios y expansión de servicios de agua potable. En otras palabras, ¿contribuye el actual modelo de distribución de agua al mejoramiento de la vida de los grupos más desfavorecidos? Al investigar estas dimensiones sociales en el manejo de agua potable, este estudio ofrece perspectivas en cuanto al diálogo amplio del desarrollo económico de Bolivia, así como asuntos de gobernanza participativa.

Three arguments are normally presented as rationale for the privatisation of state owned enterprises. The first relates to the problem of the financing of higher levels of public expenditure
the second is based on the viewpoint that private ownership is more efficient than public ownership
whilst the third claims that the losses of inefficient public enterprise are responsible for excessive budget deficits and other fiscal problems.

Although empirical evidence proves that privatisation enhances economic efficiency, it negatively affects the affordability of and access to essential services, which may have serous consequences for poorer households. This happens through increased prices of essential services, such as electricity and telecommunication, as well as through loss of employment opportunities during and after privatisation.

Many countries, also in Africa, implemented various types of privatisation programmes over the past two decades in order to decrease the relative size of governments and to improve efficient delivery of services. Towards the end the 1990&rsquo
s and after the tragic genocide, Rwanda&rsquo
s Government of National Unity also embarked on an ambitious restructuring programme of its state-owned enterprises.
The main purpose of this study was to assess the likely impact of privatisation on poor households in developing countries. The report presents a general overview of the literature, with a specific focus on Brazil, Argentina and South Africa. It investigates the experiences of these countries and derives lessons that can be learnt. Finally it assesses the possible impact of the privatisation of essential service delivery on poor households in Rwanda.

The main conclusion of the study is that governments should look beyond efficiency benefits of restructuring and focus on the overall opportunity cost of the privatisation of essential service delivery. The specific method of privatisation may determine the final social impact. The case studies also highlight the need for more research into the challenges facing the privatisation of essential service delivery. It is clear that any restructuring should be preceded by a thorough analysis of the likely impact on the poorer sections of the community.

In recent years, concern about food safety linked to health issues has seen a rise in private food safety standards in addition to the regulations set by the Food and Agriculture Organisation (FAO) in collaboration with the World Health Organisation (WHO). These have presented challenges to producers and exporters of agricultural food products especially the producers of fresh fruits and vegetables. In spite of the food safety-linked challenges from the demand side, the vast range of business-environment forces pose equally formidable challenges that negatively impact on the exporting industries’ ability to maintain or improve their market shares and their ability to compete in world markets. The objective of this study was therefore to establish the competitiveness of the South African citrus industry in the international markets within this prevailing scenario. Due to the diversity of the definitions of competitiveness as a concept, this study formulated the following working definition: “the ability to create, deliver and maintain value and constant market share through strategic management of the industrial environment or competitiveness drivers”. This was based on the understanding that the international market shares of an industry are a function of forces in the business environment which range from intra-industry, external and national as well as the international elements. The unit of analysis were the citrus producers engaged in export of their products and the study made use of 151 responses by producers. The study adopted a five-step approach to the analysis of the performance of the South African citrus industry in the global markets, starting with the analysis of the Constant Market Share (CMS) of the South African citrus industry in various world markets, establishing the impact of the business environmental factors upon competitiveness, establishing the costs of compliance with private food safety standards, determining the non-price benefits of compliance with the standards, as well as highlighting the strategies for enhancing long-term competitiveness of the industry in the international markets. South Africa is one of the top three countries dominating the citrus fruit export market. Since its entry into the citrus fruit exports market in the 1900s, the industry has sustained its activity in the international market. The Constant Market Share Analysis shows that, amidst the challenges on the international market side, and the changes in the business environment, over much of which the industry has limited control and influence, the industry has maintained its competitive advantage in several markets. The CMS shows that South Africa’s lemons are competitive in America. Despite a negative trend, the South African grapefruit has been competitive in France, Greece, Italy, the Netherlands and Spain. Oranges have been competitive in the Greece, Italy, Portugal, UK, Asian and Northern Europe markets. Competitiveness in these markets has been due to the inherent competitiveness of the industry. Competitiveness in such markets as the Middle East has been attributed to the relatively rapid growth of these markets. The South African citrus industry has similarly undergone many major processes of transformation. The business environmental factors influencing its performance have ranged reform to the challenges beyond the country’s borders. These factors directly and indirectly affect the performance of the industry in the export market. They have influenced the flow of fruits into different international destinations. Of major concern are the food safety and private standards. Challenges in traditional markets as well as opportunities presented by demand from newly emerging citrus consuming nations have seen a diversification in the marketing of the South African citrus. The intensity of competition in the global market is reflected by the fluctuations in the market shares in different markets as well as the increase and fluctuations of fruit rejection rates in some lucrative markets such as America. A combination of challenging national environmental forces and stringent demand conditions negatively impact on revenues especially from markets characterised by price competitiveness. This study identified cost of production, foreign market support systems, adaptability, worker skills, challenges of management in an international environment and government policies such as labour and trade policies as some of the most influential obstacles to competitiveness. Some of the most competiveness-enhancing factors were market availability, market size, market information, market growth and the availability of research institutions. However, compliance with private standards still poses a challenge to the exporters. The different performance levels of the industry in various markets prove the dissimilarity of the demand conditions in the global market. These are supported by the negative influence associated with the foreign market support regimes as well as the challenges associated with compliance with private food safety standards. While market availability, market growth, market information and size were identified as enhancing competitiveness, the fluctuations and inconsistencies in the competitiveness of the industry in different foreign markets require more than finding markets. Resource allocation by both the government and the industry may need to take into account the off-setting of the national challenges and support of farmers faced with distorted and unfair international playing fields. Otherwise, market availability is not a challenge for the industry save meeting the specifications therewith as well as price competitiveness which is unattainable for the South African citrus producers faced with high production costs. For the purposes of further study, it is recommended that account should be taken of all the products marketed by the industry (including processed products such as fruit juices) in order to have a whole picture of the competitiveness of the industry in the international market. This study also proffers a new theoretical framework for the analysis of the business environment for the citrus industry and other agro-businesses. This framework takes into account the indispensability of the food safety standards and measures as well as the diversity of the global consumer and the non-negotiability of food trade for the sustenance of the growing population.

A great deal of research has demonstrated that Non-Timber Forest Products (NTFPs) play a crucial role in the livelihoods of the rural poor, and are particularly important to the most marginalised people throughout the developing world. However, these livelihood benefits are not without cost to the natural resource base that rural communities depend so heavily upon. The continued dependence on NTFPs as a major livelihood source must be contingent upon the minimisation of the level of disturbance created through this dependency. This study assesses the level of disturbance created through natural resource harvesting in eight study sites around South Africa, and applies a predictive conceptual model created by Shankaar et al. (2004b) to try and ascertain under what conditions the level of disturbance created through natural resource harvesting will be high. It assesses the three key factors that Shankaar et al. (2004b) identified (level of Local Ecological Knowledge (LEK), level of dependency and access to markets) in relation to the level of disturbance found at each of the study sites. It was found that there was a statistically significant relationship between the level of dependency and the level of disturbance, but there was no statistically significant relationship between either access to markets or the level of LEK and disturbance. Regulation of land use is a key issue, with weak local institutions in communal areas making effective resource management difficult. The significance of these findings is discussed, and priorities for future research are identified. This study adds to the body of knowledge related to NTFP harvesting and critically analyses the conflicts between the livelihood gains and the level of disturbance created through NTFP harvesting in an attempt to ascertain how livelihoods can be safeguarded. And in the longer-term, so that management strategies can be identified where resource extraction is not at the cost of undermining the very livelihoods that depend upon the natural resource base.

La present tesi doctoral té la finalitat d'aconseguir una major claredat en la identificació de les dificultats en l'accés a la universitat dels estudiants procedents de vies no habituals a les universitats públiques catalanes. Aquesta fita es desplega en dos objectius generals de recerca: a) analitzar les causes que porten els estudiants a accedir a la universitat a través de vies no habituals i b) analitzar les barreres i els facilitadors que perceben els estudiants que accedeixen a la universitat a través de vies no habituals. Per finalment, proposar un model que permeti reduir les barreres i potenciar els facilitadors identificats. L'enfocament de la investigació és de naturalesa mixta, entreteixint els enfocaments qualitatiu i quantitatiu mitjançant l'aplicació d'instruments de tots dos mètodes. Els casos d'estudi seleccionats són dues vies d'accés a la universitat considerades com no habituals: a) la via 4 per a estudiants amb un títol de CFGS i assimilats, i b) la via 9 per a estudiants procedents de les proves per a majors de 25 anys. Pel que fa a la mostra, està composta per estudiants de nou accés a universitats públiques de la província de Barcelona.
La presente Tesis Doctoral tiene la finalidad de arrojar una mayor claridad en la identificación de las dificultades en el acceso a la universidad de los estudiantes procedentes de vías no habituales en las universidades públicas catalanas. Este hito se despliega en dos objetivos generales de investigación: a) analizar las causas que llevan a los estudiantes a acceder a la universidad a través de vías no habituales y b) analizar las barreras y los facilitadores que perciben los estudiantes que acceden a la universidad a través de vías no habituales. Para finalmente, proponer un modelo que permita reducir las barreras y potenciar los facilitadores identificados. El enfoque de la investigación es de naturaleza mixta, entretejiendo los enfoques cualitativo y cuantitativo mediante la aplicación de instrumentos de ambos métodos. Los casos de estudio seleccionados son dos vías de acceso a la universidad consideradas como no habituales: a) la vía 4 para estudiantes con un título de CFGS y asimilados, y b) la vía 9 para estudiantes procedentes de las pruebas para mayores de 25 años. En cuanto a la muestra, está compuesta por estudiantes de nuevo acceso en universidades públicas de la provincia de Barcelona.
The aim of this doctoral thesis is to provide greater clarity in identifying the difficulties of access to university for students coming from non-traditional backgrounds in Catalan public universities. This purpose is developed under the approach of two general research objectives: a) to analyse the causes that lead students to access university through non-traditional pathways and b) to analyse the barriers and facilitators perceived by students who access university through non-traditional routes. To finally, propose a model that aims at reducing the barriers and promote the facilitators identified. The research approach is of a mixed nature, intertwining qualitative and quantitative approaches with the application of instruments from both methods. The selected cases are two routes to access university which are considered as non-traditional pathways: a) route 4 for students with a vocational training and assimilated, and b) route 9 for students coming from the over-25 access test. As for the sample, it is composed of new entry students at public universities in the province of Barcelona.

Magister Public Health - MPH
Promoting positive and healthy decision-making practices and encouraging the utilization of health care facilities amongst adolescents is an important public health priority given that the period of adolescence is characterized by experimentation and risk taking behaviour. In the Tafelsig area of Mitchell‟s Plain, a poor socio-economic community within the Cape Town metropole, adolescents are exposed to a range of social problems (such as alcohol and substance abuse) that can potentially be harmful to their health. Given this context there was some concern raised by the sub-district health management team that adolescents are not making sufficient use of the local health facilities. The purpose of this study was to gain a greater understanding of the factors that contribute to, or hinder, the utilization by adolescents of the public health facilities in the Tafelsig area and in turn provide the Department of Health with information on adolescents‟ preferences concerning access to and use of the local primary-level health services in Mitchells Plain.An exploratory descriptive study was conducted to explore the topic using qualitative research methods. Permission to conduct the research was obtained from the Higher Degrees Committee of the University of the Western Cape and the School Principal. In-depth interviews were conducted with eight Grade 9 and seven Grade 10 male and female learners from the local secondary school - all of whom were randomly selected from a list of learners who indicated their willingness to participate in the study and who had obtained the written consent from their parents or guardian to do so. Interviews with the learners explored the positive and negative experiences, perceptions and opinions they have of using – or contemplating the use of – the local health facilities. The data from these interviews were analyzed using thematic content analysis.The study demonstrated that even when public health services are available, adolescents are often not in a position themselves to choose for themselves: their parents or guardians invariably make the choice for them. At times they are also reluctant to use public health facilities for fear of being judged by health personnel for being sexually active. The idea of waiting for long periods of time to see a health professional, or being observed at the health facility by other members of their community, are also considered to be disincentives.Many of the learners interviewed expressed a need for more information about sexual and reproductive health issues and matters that affect their health. The findings of this study also suggest that there is an urgent need for youth-friendly health services to be made available in the Mitchells Plain community. It is thus recommended that the Department of Health strategically assess whether an existing public health facility can be re-orientated to cater for the specific health needs of adolescents in Mitchells Plain.

The doctrine of intellectual property is based on the assumption that the exclusivity to commercialize a novel product granted to an inventor creates incentives to conduct research. In some areas, however, intellectual property can constitute a barrier to development of social welfare. In the area of access to medicines in developing countries, the intellectual property-related problem can take two forms. When needed products are not being developed and thus do not exist, lack of availability occurs. Lack of accessibility, on the other hand, arises when necessary medicines do exist, but their prices are prohibitive for people from resource-poor countries. Based on a detailed analysis of the patent and trade environment in the pharmaceutical sector, the thesis examines the potential of patent pooling as a joint intellectual property management strategy to increase access to medicines within the existing international intellectual property system. Particularly, it analyzes the effects of an existing pharmaceutical pool, the Medicines Patent Pool, on accessibility of antiretroviral medicines in low and middle income countries.

Mestrado em Engenharia Eletrónica e Telecomunicações
The mobile networks market (focus of this work) strategy is based on the consolidation of the installed structure and the optimization of the already existent resources. The increasingly competition and aggression of this market requires, to the mobile operators, a continuous maintenance and update of the networks in order to obtain the minimum number of fails and provide the best experience for its subscribers. In this context, this dissertation presents a study aiming to assist the mobile operators improving future network modifications. In overview, this dissertation compares several forecasting methods (mostly based on time series analysis) capable of support mobile operators with their network planning. Moreover, it presents several network indicators about the more common bottlenecks.
A estratégia comum dos operadores no mercado das redes móveis (área onde este trabalho se debruça) passa por uma consolidação da sua rede base já instalada e pela otimização dos recursos já existentes. A crescente competitividade e agressividade deste mercado obrigam a que os operadores mantenham a sua rede atualizada e com o menor número de falhas possível, com a finalidade de oferecer a melhor experiência aos seus utilizadores. Neste contexto, esta dissertação apresenta um estudo que auxilia os operadores a aperfeiçoar futuras alterações na sua rede. De um modo geral, esta dissertação compara alguns métodos de previsão (baseados maioritariamente na análise de séries temporais) capazes de assistir os operadores no planeamento da sua rede e ainda apresenta alguns indicadores de rede onde as limitações de desempenho são mais frequentes.

Nous étudions dans cette thèse le problème de l'indépendance physique des données dans les bases de données XML. Dans une première partie de cette thèse nous proposons les modules d'accès XML (XML Access Modules ou XAMs) - un langage de motifs d'arbre conçu pour exprimer un grand sous-ensemble de XQuery, et enrichi avec des noeuds optionnels (permettant de capturer des motifs qui couvrent plusieurs requêtes imbriquées) et des identiants structurels (qui augmentent les possibilités de réécriture). Nous démontrons que ce langage des vues peut être utilise pour décrire uniformément un grand nombre de schémas de stockage, d'index et de vues matérialisées. Dans une deuxième partie de cette thèse nous étudions le problème de la réécriture des requêtes XQuery à travers des vues exprimées par des modules d'accès XML. Dans un premier temps, nous présentons un algorithme capable d'extraire des motifs XAM à partir des requêtes XQuery et nous démontrons l'importance d'utiliser des vues qui peuvent enjamber plusieurs blocs XQuery imbriqués. Par la suite, nous étudions le problème de la réécriture des requêtes en utilisant des vues materialisées, où la requête et les vues sont décrites par des vues XAM. Nous caractérisons la complexité de l'inclusion de motifs d'arbre et de la réécriture des requêtes sous les contraintes exprimées par des résumés structurels, dont une forme augmentée permettra également d'exprimer des contraintes d'intégrité
The purpose of this thesis is to design a framework for achieving the goal of physical data independence in XML databases. We first propose the XML Access Modules - a rich tree pattern language featuring multiple returned nodes, nesting, structural identifiers and optional nodes, and we show how it can be used to uniformly describe a large set of XML storage schemes, indices and materialized views. A second part of this thesis focuses on the problem of XQuery rewriting using XML Access Modules. As a first step of our rewriting approach we present an algorithm to extract XML Access Modules patterns from XQuery and we show that the patterns we identify are strictly larger than in previous works, and in particular may span over nested XQuery blocks. We characterize the complexity of tree pattern containment (which is a key subproblem of rewriting) and rewriting itself, under the constraints expressed by a structural summary, whose enhanced form also entails integrity constraints. We also show how to exploit the structural identifiers from the view definitions in order to enhance the rewriting opportunities

Avec le développement des technologies portables, les mémoires de type flash sont de plus en plus utilisées. Les compétences requises pour répondre au marché florissant augmentent chaque année. Cependant, les technologies actuelles sont basées sur l’intégration de transistors. Leurs performances impliquent un long temps d’écriture et des tensions d’opérations importantes. La technologie Resistive Random Access Memory (RRAM) permet de répondre aux problématiques liées aux mémoires de type flash. La simplicité de fabrication de ces mémoires permet une forte densité d’intégration à faible coût. Également, les performances attendues par cette technologie dépassent les performances actuelles de Dynamic Random Access Memory (DRAM). Les études réalisées actuellement au sein de la communauté scientifique permettent de déterminer les meilleures performances selon le choix des matériaux. Les premières études se concentraient sur l’oxyde de titane TiO2 en tant qu’isolant, puis avec l’augmentation de l’intérêt envers cette technologie le nombre d’oxydes étudiés s’est élargi. Les dispositifs conventionnels utilisent une couche d’oxyde comprise entre deux électrodes métalliques. En augmentant la densité de dispositifs dans des circuits en matrices croisées, l’isolation entre les points mémoires n’est pas garantie et les courants de fuites deviennent un facteur limitant. Pour éviter ces problèmes, le contrôle de chaque cellule est réalisé par un transistor, on parle d’architecture 1T1R avec n transistors nécessaires pour n points mémoires. En 2008 Dubuc[1] propose un nouveau procédé de fabrication: le procédé nanodamascène. En adaptant ce procédé, et en disposant deux cellules dos à dos, nous créons un composant qui ne nécessite plus de transistor de contrôle [2]. Cela permet, en outre, de réduire les courants de fuite et simplifie l’adressage de chaque cellule. Les dispositifs sont incorporés dans une couche offrant une surface planaire. Il n’y a pas de limite technique à la superposition des couches, ce qui permet une haute densité d’intégration dans le Back-end-of-line du CMOS (Complementary Metal Oxyde Semiconductor), offrant de nouveaux horizons à la technologie RRAM. Suivant les éléments précédents, mon projet de maîtrise a pour objectif de démontrer la possibilité de fabriquer des cellules RRAM en utilisant le procédé nanodamascène. Ce développement implique la fabrication, pour la première fois, de dispositifs micrométriques de type croisés et planaires en utilisant des architectures dont la fabrication est maîtrisée au sein du laboratoire. Cela permettra de mettre au point les différentes procédés de fabrication pour les deux types de dispositifs, de se familiariser avec les techniques de caractérisation électrique, d’acquérir des connaissances sur les matériaux actifs, et proposer des premiers dispositifs RRAM.

Dans le cadre du développement international du mouvement du libre accès aux publications scientifiques, cette thèse analyse plus précisément la situation française dans le contexte européen. Cette analyse a été menée à travers une démarche de recherche-action, au sein d'un groupe d'acteurs du Groupement français des industries de l'information (GFII) concernés par le libre accès.Nous cherchons tout d'abord à mettre en évidence les forces motrices du développement du libre accès en nous appuyant sur une méthodologie prospective développée au LIPSOR/CNAM.Les résultats nous ont conduit à contribuer à la conception d'un site d'information dont la finalité est l'affichage des politiques des éditeurs nationaux en matière d'auto-archivage afin d'accompagner les pratiques de dépôts au niveau national. L'analyse prospective a en effet révélé l'importance des embargos pour les équilibres financiers des éditeurs.De façon plus distanciée, nous amorçons également une réflexion sur l'impact réel du libre accès sur deux moteurs semblant jouer un rôle croissant dans l'économie de la connaissance, à savoir la créativité et l'interdisciplinarité.

La complexité du récepteur optimal de Verdu pour le système CDMA augmente exponentiellement avec le nombre d'utilisateurs, de sorte que ce récepteur devient difficilement réalisable. Dans cette thèse, nous analysons le récepteur sub-optimal d'annulation d'interférences de structure parallèle à plusieurs étages (PIC). La nature parallèle de l'algorithme est facilement exploitable dans un environnement de multitraitement. Ceci le rend extrêmement attrayant pour le système UMTS-TDD. L'utilisation d'un estimateur du type filtre adapté, a comme conséquence l'apparition d'un biais dans l'amplitude estimée en sortie du second étage, particulièrement dans le cas d'un système chargé. Ce biais dégrade les performances en terme de taux d'erreur par bit (TEB) du système. Nous proposons une approche originale de faible complexité pour réduire le biais, dans laquelle on n'atténue pas l'estimation de l'interférence d'accès multiple (MAI), comme dans la méthode d'annulation partielle, mais on amplifie plutôt l'amplitude du signal reçu pour chaque utilisateur par un coefficient scalaire que nous appelons le facteur d'amplification (FA). Une étude, analytique dans le cas synchrone et par simulation dans le cas asynchrone, a été conduite pour déterminer une valeur optimale de ce facteur d'amplification, afin de réduire au minimum le taux d'erreurs par bit (TEB). Nous indiquons les performances obtenues dans les cas d'un contrôle de puissance parfait et d'un effet proche-lointain non compensé. Nous proposons ensuite une structure incorporant ce facteur d'amplification dans le cas de plusieurs étages, et nous comparons sa complexité avec celle de la solution utilisant l'annulation partielle. Un autre aspect traité dans cette thèse est l'étude de l'impact des fonctions de décision utilisées sur la performance du récepteur PIC. Nous avons ainsi considéré les fonctions dites ‘null zone' et ‘clipping' et comparé leur sensibilités à l'erreur d'optimisation du seuil de décision
The complexity of Verdu's optimal receiver for CDMA increases exponentially with the number of users, loading to an unrealistic implementation. In this thesis, we analyze the sub-optimal interference cancellation receiver with multi-stages parallel structure. The parallel nature of the algorithm can be easily exploited in a multiprocessing environment. This makes it extremely attracting for UMTS-TDD. The use of a matched-filter estimator, results in a bias in the estimated amplitude at the second stage output, particularly for heavy system loads. This bias degrades the system performances in term of bit error rate (BER). We propose an original low complexity approach for reducing the bias, in which we don't attenuate the estimated multiple access interference (MAI), as in the partial cancellation method, but we amplify the amplitude of the received signal for each user by a scalar which we call the amplification factor (AF). An analytical study in the synchronous case and by simulation in the asynchronous case was led to determine an optimal value of this amplification factor, in order to minimize the BER. We indicate the performances obtained in a perfect power control case and for uncompensated near-far effects. Then, we propose a structure incorporating this amplification factor in the multi-stage case, and we compare its complexity with that for the partial cancellation solution. Another aspect considered in this thesis is the impact of the decision functions on the performance of the PIC receiver. We thus considered the `null zone' and ` clipping' functions and compared their sensitivity to decision threshold optimization errors

Network administration has become more difficult as the number of Internet users has grown and customer usage patterns have changed over time. Rapidly increasing subscriber bases, data intensive applications (such as streaming audio and video), heavy Web browsing, and large file downloads require significant resources and may tax existing network bandwidth. Reliability and quality of service are becoming serious issues for service providers across the country. Due to the dynamic nature of the information technology (IT) sector in general, it is difficult to predict future network usage patterns or what types of applications may be available, and how these applications may be used over time. This research presents a methodology to facilitate capacity planning and to improve the evaluation of network performance for connection-based networks using the Virginia Tech modem pool as a test bed. The abstract research question is can innovative business strategies be employed in lieu of, or in addition to, traditional management practices such as adding capacity in order to improve the performance of a dialup network? Examples of such strategies or business rules may include limiting the duration of an online session or limiting the number of times a given customer can dial into the pool in a specified time period. A complete network traffic characterization is conducted based on service time and interarrival time variables. A longitudinal analysis is performed to examine how traffic patterns have changed over time. Finally, a simulation model is utilized to examine how imposing different business rules during peak-periods of operation can reduce the blocking probability and improve the overall level-of-service. The potential contribution of this research appears to be significant based on the lack of existing literature.
Ph. D.

Le phénomène des accents étrangers, bien qu'étudié par de nombreux chercheurs, n'est clairement défini ni au niveau de son origine (physiologique ou psychologique) ni de sa nature (interférences ou langue intermédiaire). De plus l'auditeur natif n'est pas en mesure de décrire les sensations auditives qui l'ont conduit à identifier l'origine de son interlocuteur. Une synthèse d'articles mène à l'élaboration d'hypothèses sur les accents étrangers. Le message parlé a une existence physique qui peut être étudiée objectivement : le signal acoustique. Les enregistrements digitalisés de mots français prononcés par des allemands et des français sont traités par différentes méthodes afin de mettre en évidence des caractéristiques de l'accent allemand. Les études combinées de la représentation temporelle, d'une analyse de Fourier, du taux de passages à zéro et des spectres de voyelles permettent une bonne visualisation des paramètres recherchés. Les résultats d'une analyse perceptuelle sont comparés aux données acquises sur les signaux. On en déduit des hypothèses sur l'accent allemand, qui seront vérifiées par l'analyse d'une seconde série de mots. Ces deux analyses confortent l'hypothèse de la langue intermédiaire et mettent en évidence l'importance de la coarticulation. Il existe des contextes phonémiques et phonologiques favorables et défavorables. Les problèmes sont dépendants du locuteur.

Els darrers anys han experimentat un augment de la demanda de serveis interactius per satèl·lit per al gran consum, cobrint serveis fixes i mòbils, tal i com accés de banda ampla, comunicacions màquina-màquina (M2M), supervisió, control i adquisició de dades (SCADA), transaccions i aplicacions de seguretat crítiques. Aquestes xarxes de comunicacions es caracteritzen per tenir una gran població d’usuaris compartint l’amplada de banda amb unes condicions de tràfic molt dinàmiques. Concretament, en el canal de retorn (de l’usuari a la xarxa) de xarxes d’accés de banda ampla, els usuaris residencials generen grans ràfegues de tràfic amb períodes d’inactivitat freqüents. Una situació similar succeeix en xarxes de comunicacions mòbils per satèl·lit, on una gran població de terminals generen transmissions infreqüents de senyalització, serveis basats en la localització or altres aplicacions de missatgeria. Aquests serveis requereixen el desenvolupament de protocols d’accés múltiple eficients que puguin operar en les condicions descrites anteriorment. Els protocols d´accés aleatori són bons candidats per servir tràfic poc predictiu, amb transmissions infreqüents així com sensibles amb el retard. A més, els protocols d´accés aleatori suporten un gran nombre de terminals compartint el canal de comunicacions i requereixen poca complexitat en el terminals. El protocols d´accés aleatori han estat àmpliament estudiats i desplegats en xarxes terrestres, però les seves prestacions són pobres en el entorn satèl·lital, que està caracteritzat per retards de propagació molt grans. Avui en dia, el seu ús en les xarxes de comunicacions per satèl·lit està principalment limitat a la senyalització d’inici de sessió, transmissió de paquets de control i en alguns casos a la transmissió de petits volums de dades amb unes eficiència d’utilització del canal molt baixa. Aquesta tesi proposa tres noves tècniques d’accés aleatori, bens adaptades per proveir els serveis esmentats anteriorment en un entorn satèl·lital, amb altes prestacions i una complexitat en el terminal d’usuari reduïda. Les noves tècniques d’accés aleatori són Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) i Enhanced Spread Spectrum Aloha (E-SSA), adaptades per un tipus d’accés ranurat, asíncron i d’espectre eixamplat respectivament. Les tres tècniques utilitzen una codificació de canal (FEC) robusta, capaç d’operar en front de interferències elevades, que són típiques en l’accés aleatori, i d’un mecanisme de cancel·lació successiva d’interferència que s’implementa en el receptor sobre els paquets descodificats satisfactòriament. Els nous protocols obtenen un throughput normalitzat superior a 1 bit/s/Hz amb una tassa de pèrdua de paquets inferior a 10-3, el qual representa un factor de millora de 1000 respecte a protocols d’accés aleatori tradicionals com l’ALOHA ranurat. Les prestacions de les noves tècniques d’accés aleatori has estat analitzades per mitjà de simulacions, així com amb nou models analítics desenvolupats en aquesta tesi capaços de caracteritzar el tràfic, la distribució estadística de la potència dels paquets, les prestacions de la codificació de canal (FEC) i el procés de cancel·lació d’interferència successiva.
Los últimos años han experimentado un crecimiento de la demanda de servicios interactivos por satélite para el gran consumo, cubriendo servicios fijos i móviles, como el acceso de banda ancha, comunicaciones máquina a máquina (M2M), supervisión, control y adquisición de datos (SCADA), transacciones i aplicaciones criticas de seguridad. Estas redes de comunicaciones se caracterizan por tener una gran población de usuarios compartiendo el ancho de banda en unas condiciones de tráfico muy dinámicas. Concretamente, en el canal de retorno (del usuario a la red) de redes de acceso de banda ancha, los usuarios residenciales generan grandes ráfagas de tráfico con periodos frecuentes de inactividad. Una situación similar ocurre en las redes de comunicaciones móviles por satélite, donde una gran población de terminales generan transmisiones infrecuentes de señalización, servicios basados en la localización u otras aplicaciones me mensajería. Estos servicios requieren el desarrollo de protocolos de acceso múltiple eficientes capaces de operar en las condiciones descritas anteriormente. Los protocolos de acceso aleatorio son buenos candidatos para servir el tráfico poco predictivo, con transmisiones infrecuentes así como sensibles al retardo. Además, los protocolos de acceso soportan un gran número de terminales compartiendo el canal de comunicaciones y requieren poca complejidad en los terminales. Los protocolos de acceso aleatorio han estado ampliamente estudiados i desplegados en las redes terrestres, pero sus prestaciones son pobres en el entorno satelital, que se caracteriza por retardos de comunicaciones muy elevados. Hoy en día, su uso en la redes de comunicaciones por satélite está principalmente limitado a la señalización de inicio de sesión, transmisión de pequeños volumenes de datos con eficiencia de utilización del canal muy baja. Esta tesis propone tres nuevas técnicas de acceso aleatorio bien adaptadas para proveer los servicios mencionados anteriormente en un entorno de comunicaciones por satélite, con altas prestaciones y una complejidad en el terminal de usuario reducida. Las nuevas técnicas de acceso aleatorio son Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) y Enhanced Spread Spectrum Aloha (E-SSA), adaptadas para un tipo de acceso ranurado, asíncrono y de espectro ensanchado respectivamente. Las tres técnicas utilizan una codificación de canal (FEC) robusta, capaz de operar en condiciones de interferencia elevadas, que son típicas en el acceso aleatorio, y de un mecanismo de cancelación sucesiva de interferencias que se implementa en el receptor sobre los paquetes que han sido decodificados satisfactoriamente. Los nuevos protocolos obtienen un throughput normalizado superior a 1 bit/s/Hz con una tasa de pérdida de paquetes inferior a 10-3, lo cual representa un factor de mejora de 1000 respecto a los protocolos de acceso aleatorio tradicionales como el ALOHA ranurado. Las prestaciones de las nuevas técnicas de acceso aleatorio han sido analizadas con simulaciones así como con nuevos modelos analíticos desarrollados en esta tesis, capaces de caracterizar el tráfico, la distribución estadística de la potencia de los paquetes, las prestaciones de la codificación de canal (FEC) y el proceso de cancelación sucesiva de interferencias.
Over the past years there has been a fast growing demand for low-cost interactive satellite terminals supporting both fixed and mobile services, such as consumer broadband access, machine-to-machine communications (M2M), supervisory control and data acquisition (SCADA), transaction and safety of life applications. These networks, are generally characterized by a large population of terminals sharing the available resources under very dynamic traffic conditions. In particular, in the return link (user to network) of commercial satellite broadband access networks, residential users are likely to generate a large amount of low duty cycle bursty traffic with extended inactivity periods. A similar situation occurs in satellite mobile networks whereby a large number of terminals typically generate infrequent packets for signaling transmission as well for position reporting or other messaging applications. These services call for the development of efficient multiple access protocols able to cope with the above operating conditions. Random Access (RA) techniques are by nature, good candidates for the less predictive, low duty cycle as well as time sensitive return link traffic. Besides, RA techniques are capable of supporting large population of terminals sharing the same capacity and require low terminal complexity. RA schemes have been widely studied and deployed in terrestrial networks, but do not perform well in the satellite environment, which is characterized by very long propagation delays. Today, their use in satellite networks is mainly limited to initial network login, the transmission of control packets, and in some cases, for the transmission of very small volumes of data with very low channel utilization. This thesis proposes three novel RA schemes well suited for the provision of the above-mentioned services over a satellite environment with high performance and low terminal complexity. The new RA schemes are Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) and Enhanced Spread Spectrum Aloha (E-SSA), suited for slotted, unslotted and spread spectrum-based systems respectively. They all use strong Forward Error Correction (FEC) codes, able to cope with heavy co-channel interference typically present in RA, and successive interference cancellation implemented over the successfully decoded packets. The new schemes achieve a normalized throughput above 1 bit/s/Hz for a packet loss ratio below 10-3, which represents a 1000-fold increase compared to Slotted ALOHA. The performance of the proposed RA schemes has been analyzed by means of detailed simulations as well as novel analytical frameworks that characterize traffic and packets power statistical distributions, the performance of the FEC coding as well as the iterative interference cancellation processing at the receiver.

Avec des prévisions de milliards d'appareils connectés, l'Internet des objets (IoT) est le moteur de l'évolution des réseaux de communication sans fil. Cette augmentation exponentielle du nombre d'appareils connectés s'accompagne d'une prolifération d'applications hétérogènes et de nouveaux cas d'utilisation sans fil très différents des services multimédias classiques. Par rapport aux systèmes de communication classiques, les systèmes de communication sans fil de prochaine génération devraient offrir des débits de données très élevés, une grande fiabilité, une faible latence, une amélioration de la qualité de service (QoS) perçue par les utilisateurs ainsi qu'une augmentation du nombre d'utilisateurs pris en charge. Pour répondre à ces exigences, certains des éléments clés que les futurs systèmes de communication doivent exploiter comprennent de nouvelles techniques d'accès au spectre telles que l'accès multiple non orthogonal (NOMA) et l'accès au spectre non coordonné, les réseaux auto-organisés (SON) et les réseaux de communication assistés par des drones (UAV). L'objectif principal de cette thèse est d'exploiter ces éléments clés pour fournir de nouvelles solutions d'allocation de ressources et de configuration de réseaux qui visent à optimiser l'utilisation des ressources radio disponibles dans ces systèmes de prochaine génération. Diverses configurations sont considérées, comprenant les systèmes sans fil avec trafic hétérogène, l'accès non coordonné au spectre dans les SON et les systèmes de communication assistés par des drones. Pour chaque configuration, une solution exploitant la technique NOMA est proposée. Les résultats ainsi obtenus montrent que les solutions proposées surpassent les techniques de l’état de l’art
With a forecasted number of billions of connected devices, the Internet of Things (IoT) is driving the evolution of wireless communication networks. This exponential increase in the number of connected devices is accompanied by a proliferation of heterogeneous IoT applications, resulting in the emergence of new wireless use cases that greatly differ from conventional multimedia services. When compared to previous communication systems, next generation wireless communication systems are expected to provide very high data rates, high reliability, low latency, improvement in the quality of service (QoS) perceived by users and an increase in the number of supported users.To meet these requirements, some of the key elements future communication systems must leverage include novel spectrum access techniques such as non-orthogonal multiple access (NOMA) and uncoordinated spectrum access, self-organized networks (SON) and unmanned aerial vehicles (UAV)-aided communication networks. The main objective of this thesis is to exploit these key elements to provide novel resource allocation and net-work design solutions that aim at optimizing the use of available radio resources in next generation wireless communication networks. Different settings are considered, spanning wireless systems with heterogeneous mobile traffic requirements, uncoordinated spectrum access in SONs and UAV-aided communication systems. For each setting, a solution leveraging NOMA scheduling is proposed. The obtained results of the proposed solutions are promising, where these solutions are shown to outperform existing techniques from the literature

Doutoramento conjunto (MAP-Tele) em Engenharia Eletrotécnica/Telecomunicações
A proliferação de diversos tipos de dispositivos moveis, aplicações e serviços com grande necessidade de largura de banda têm contribuído para o aumento de ligações de banda larga e ao aumento do volume de trafego das redes de telecomunicações moveis. Este aumento exponencial tem posto uma enorme pressão nos mobile operadores de redes móveis (MNOs). Um dos aspetos principais deste recente desenvolvimento, é a necessidade que as redes têm de oferecer baixa complexidade nas ligações, como também baixo consumo energético, muito baixa latência e ao mesmo tempo uma grande capacidade por baixo usto. De maneira a resolver estas questões, os MNOs têm focado a sua atenção na redes de acesso por rádio em nuvem (C-RAN) principalmente devido aos seus benefícios em termos de otimização de performance e relação qualidade preço. O standard para a distribuição de sinais sem fios por um fronthaul C-RAN é o common public radio interface (CPRI). No entanto, ligações óticas baseadas em interfaces CPRI necessitam de uma grande largura de banda. Estes requerimentos podem também ser atingidos com uma implementação em ligação free space optical (FSO) que é um sistema ótico que usa comunicação sem fios. O FSO tem sido uma alternativa muito apelativa aos sistemas de comunicação rádio (RF) pois combinam a flexibilidade e mobilidade das redes RF ao mesmo tempo que permitem a elevada largura de banda permitida pelo sistema ótico. No entanto, as ligações FSO são suscetíveis a alterações atmosféricas que podem prejudicar o desempenho do sistema de comunicação. Estas limitações têm evitado o FSO de ser tornar uma excelente solução para o fronthaul. Uma caracterização precisa do canal e tecnologias mais avançadas são então necessárias para uma implementação pratica de ligações FSO. Nesta tese, vamos estudar uma implementação eficiente para fronthaul baseada em tecnologia á rádio-sobre-FSO (RoFSO). Propomos expressões em forma fechada para mitigação das perdas de propagação e para a estimação da capacidade do canal de maneira a aliviar a complexidade do sistema de comunicação. Simulações numéricas são também apresentadas para formatos de modulação adaptativas. São também considerados esquemas como um sistema hibrido RF/FSO e tecnologias de transmissão apoiadas por retransmissores que ajudam a alivar os requerimentos impostos por um backhaul/fronthaul de C-RAN. Os modelos propostos não só reduzem o esforço computacional, como também têm outros méritos, tais como, uma elevada precisão na estimação do canal e desempenho, baixo requisitos na capacidade de memória e uma rápida e estável operação comparativamente com o estado da arte em sistemas analíticos (PON)-FSO. Este sistema é implementado num recetor em tempo real que é emulado através de uma field-programmable gate array (FPGA) comercial. Permitindo assim um sistema aberto, interoperabilidade, portabilidade e também obedecer a standards de software aberto. Os esquemas híbridos têm a habilidade de suportar diferentes aplicações, serviços e múltiplos operadores a partilharem a mesma infraestrutura de fibra ótica.
The proliferation of different mobile devices, bandwidth-intensive applications and services contribute to the increase in the broadband connections and the volume of traffic on the mobile networks. This exponential growth has put considerable pressure on the mobile network operators (MNOs). In principal, there is a need for networks that not only offer low-complexity, low-energy consumption, and extremely low-latency but also high-capacity at relatively low cost. In order to address the demand, MNOs have given significant attention to the cloud radio access network (C-RAN) due to its beneficial features in terms of performance optimization and cost-effectiveness. The de facto standard for distributing wireless signal over the C-RAN fronthaul is the common public radio interface (CPRI). However, optical links based on CPRI interfaces requires large bandwidth. Also, the aforementioned requirements can be realized with the implementation of free space optical (FSO) link, which is an optical wireless system. The FSO is an appealing alternative to the radio frequency (RF) communication system that combines the flexibility and mobility offered by the RF networks with the high-data rates provided by the optical systems. However, the FSO links are susceptible to atmospheric impairments which eventually hinder the system performance. Consequently, these limitations prevent FSO from being an efficient standalone fronthaul solution. So, precise channel characterizations and advanced technologies are required for practical FSO link deployment and operation. In this thesis, we study an efficient fronthaul implementation that is based on radio-on-FSO (RoFSO) technologies. We propose closedform expressions for fading-mitigation and for the estimation of channel capacity so as to alleviate the system complexity. Numerical simulations are presented for adaptive modulation scheme using advanced modulation formats. We also consider schemes like hybrid RF/FSO and relay-assisted transmission technologies that can help in alleviating the stringent requirements by the C-RAN backhaul/fronthaul. The propose models not only reduce the computational requirements/efforts, but also have a number of diverse merits such as high-accuracy, low-memory requirements, fast and stable operation compared to the current state-of-the-art analytical based approaches. In addition to the FSO channel characterization, we present a proof-of-concept experiment in which we study the transmission capabilities of a hybrid passive optical network (PON)-FSO system. This is implemented with the real-time receiver that is emulated by a commercial field-programmable gate array (FPGA). This helps in facilitating an open system and hence enables interoperability, portability, and open software standards. The hybrid schemes have the ability to support different applications, services, and multiple operators over a shared optical fiber infrastructure.

Doutoramento em Ciências da Computação
Web-based technologies have been increasingly used in Picture Archive and Communication Systems (PACS), in services related to storage, distribution and visualization of medical images. Nowadays, many healthcare institutions are federating services and outsourcing their repositories to the Cloud. However, managing communications between multiple geo-distributed locations is still challenging due to the complexity of dealing with huge volumes of data and bandwidth limitations. Communication latency is a critical issue that still hinders the adoption of this paradigm. In order to improve the performance of distributed medical imaging networks, routing mechanisms with cache and prefetching can be used. This doctorate proposes a cache architecture based on static rules together with pattern recognition for both cache eviction and prefetching.
As tecnologias Web têm sido usadas cada vez mais no universo dos Picture Archiving and Communication Systems (PACS), nomeadamente em serviços de armazenamento, distribuição e visualização de imagem médica. Atualmente, verificamos que existe uma tendências para as instituições partilharem fluxos de trabalho e contratualizarem serviços na Cloud. No entanto, gerir as comunicações entre entidades geograficamente distribuídas continua a ser um desafio complexo devido ao enorme volume de dados e às limitações de largura de banda. A latência de acesso remoto aos dados é um problema importante que dificulta a adopção deste paradigma. Para melhorar o desempenho de redes distribuídas de imagem médica, podemos utilizar mecanismos de encaminhamento com cache e prefetching. Este doutoramento propõe uma arquitetura de cache baseada em regras estáticas e reconhecimento de padrões para prefetching e limpeza da cache.

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Today there exist a myriad of different types of physical access control systems (PACS) that use a smart card or mobile device as a key. The mobile device enabled smart locks, as they are often referred to, operate using either Wi-Fi or Bluetooth. This thesis has explored the use of a third emerging wireless technology called Near Field Communication (NFC) available in mobile devices such as smartphones. Near Field Communication (NFC) technology is a relatively new technology that is on the rise and is included in almost every new mobile device. By leveraging Near Field Communication (NFC) enabled mobile devices, a highly secure access control system can be achieved and developed taking advantage of the computational power of smartphones in comparison to traditional methods the business implications are huge, Several different authentication and encryption protocols, mobile operating systems and Near Field Communication (NFC) modes of operation where analyzed and evaluated. After considerations technical considerations the Secure Remote Password authentication protocol on top of Near Field Communication (NFC) card emulation (CE) scheme with the client application running on smartphones operating system (OS) was selected. This thesis shows that Near Field Communication (NFC) enables a mobile device to act as a key in a secure access control system (PACS) and as the user base for NFC grows larger so will the likelihood that we will come to see more of these types of systems in business and organizations.

Le travail de recherche présenté dans cette thèse est basé sur l’étude du protocole de communication par satellite appelé « Enhanced Spread Spectrum Aloha » (E-SSA) et créé par l’Agence Spatiale Européenne (ESA) en 2009. Il s’agit d’une technique qui permet à un terminal d’envoyer des messages courts par satellite de manière totalement asynchrone. L’intérêt est de maximiser l’efficacité spectrale tout en gardant une complexité minimale du terminal grâce aux techniques d’étalement de spectre et d’annulation d’interférences (SIC). Alors qu’au départ le protocole E-SSA avait pour but d’apporter un support physique pour des applications destinées à des terminaux mobiles en bande S, les développements se sont récemment étendus à une gamme de terminaux fixes dans des bandes de fréquence différentes (C, Ku ou Ka). À partir de ces deux modèles d’utilisation de l’E-SSA, ce travail de recherche se concentre sur la mise en place de solutions techniques permettant d’augmenter significativement la capacité globale du système. Cela est possible à travers une optimisation des différents paramètres du protocole et la conception d’algorithmes de gestion des puissances des terminaux
The work presented in this thesis focuses on the satellite communication protocol named “Enhanced Spread Spectrum Aloha” (E-SSA) and developed in 2009 by the European Space Agency (ESA). The E-SSA structure, based on fully asynchronous random access, perfectly copes with low-duty cycle bursty transmissions adapted to satellite messaging. High performance in terms of spectral efficiency is possible by exploiting iterative successive interference cancellation (SIC) while keeping minimal complexity at the terminal side. If the first exploitation of the protocol concerned mobile applications in S-band, it has been extended to fleets of fixed terminals in other frequency bandwidths (C, Ku or Ka). Starting from these two scenarios, this thesis proposes different innovations to further boost the E-SSA global system capacity. These technical solutions particularly include a fine optimization of protocol parameters and new power control algorithms

L'importance des systèmes collaboratifs a considérablement augmenté au cours des dernières années. La majorité de nouvelles applications sont conçues de manière distribuée pour répondre aux besoins du travail collaboratif. Parmi ces applications, nous nous intéressons aux éditeurs collaboratifs temps-réel (RCE) qui permettent la manipulation de divers objets partagés, tels que les pages wiki ou les articles scientifiques par plusieurs personnes réparties dans le temps et dans l'espace. Bien que ces applications sont de plus en plus utilisées dans de nombreux domaines, l'absence d'un modèle de contrôle d'accès adéquat limite l'exploitation de leur plein potentiel. En effet, contrôler les accès aux documents partagés de façon décentralisée et sans alourdir les performances du système collaboratif représente un vrai challenge, surtout que les droits d'accès peuvent changer fréquemment et de façon dynamique au cours du temps. Dans cette thèse, nous proposons un modèle de contrôle d'accès générique basé sur l'approche de réplication optimiste du document partagé ainsi que sa politique de contrôle d'accès. Pour cela, nous proposons une approche optimiste de contrôle d'accès dans la mesure où un utilisateur peut violer temporairement la politique de sécurité. Pour assurer la convergence, nous faisons recours à l'annulation sélective pour éliminer l'effet des mises à jour illégales. Vu l'absence d'une solution d'annulation générique et correcte, nous proposons une étude théorique du problème d'annulation et nous concevons une solution générique basée sur une nouvelle sémantique de l'opération identité. Afin de valider notre approche tous nos algorithmes ont été implémentés en Java et testés sur la plateforme distribuée Grid'5000
The importance of collaborative systems in real-world applications has grown significantly over the recent years. The majority of new applications are designed in a distributed fashion to meet collaborative work requirements. Among these applications, we focus on Real-Time Collaborative Editors (RCE) that provide computer support for modifying simultaneously shared documents, such as articles, wiki pages and programming source code by dispersed users. Although such applications are more and more used into many fields, the lack of an adequate access control concept is still limiting their full potential. In fact, controlling access in a decentralized fashion for such systems is a challenging problem, as they need dynamic access changes and low latency access to shared documents. In this thesis, we propose a generic access control model based on replicating the shared document and its authorization policy at the local memory of each user. We consider the propagation of authorizations and their interactions. We propose a optimistic approach to enforce access control in existing collaborative editing solutions in the sense that a user can temporarily violate the access control policy. To enforce the policy, we resort to the selective undo approach in order to eliminate the effect of illegal document updates. Since, the safe undo is an open issue in collaborative applications. We investigate a theoretical study of the undo problem and propose a generic solution for selectively undoing operations. Finally, we apply our framework on a collaboration prototype and measure its performance in the distributed grid GRID?5000 to highlight the scalability of our solution

Cette thèse a pour objet l'amélioration de la sécurité de systèmes à accès distant par l'utilisation d'outils cryptographiques. Elle s'applique en particulier aux applications de gestion de documents numériques pour leurs problématiques de communication, d'authentification et de gestion de droits. Contrairement aux approches classiques consistant à utiliser des moyens de protections ponctuels, nous proposons ici un ensemble d'outils conçu pour collaborer afin de renforcer la sécurité du système. La sécurisation des communications est réalisée grâce à la conception d'un protocole de communications sécurisée adapté aux applications distribuées. Les problématiques d'authentification ont donné lieu à l'élaboration de solutions permettant d'apporter un support cryptographique pour toutes modalités d'authentification. La gestion des droits fait l'objet d'un développement spécifique permettant d'associer des droits à des applications cryptographiques. Un point clé de ces réflexions est l'importance de l'accessibilité de ces outils de sécurité pour les utilisateurs du système. Cela a influé sur les propositions pour qu'elles perturbent le moins possible l'expérience utilisateur. Le résultat est l'intégration en un système global de différents outils et mécanismes apportant une sécurité complète à un système de gestion de documents numériques. Cette sécurité est basée sur des algorithmes cryptographiques afin de disposer de propriétés de sécurité prouvables et vérifiables. Comme support de ces mécanismes, une plate-forme de sécurité logicielle a été conçu pour fournir les outils cryptographiques de façon portable
This thesis' goal is the improvement of the security of remotely accessed systems with the use of cryptographic tools. Specifically it is applied to digital documents management software that raise issues in three fields~: communication, authentication and rights management. Unlike common approaches that involve the use of individual protections for these three fields, we offer a set of tools made to work together to improve the system's security. Securing communication is done thanks to a new secure communication protocol designed for distributed applications. Authentication issues led to the development of two tailored solutions providing cryptographic support to the application for any authentication method. Rights management is handled through new associations between a given access right and specific cryptographic applications. A key element of those solutions is the emphasis put on the usability of these secure tools. It swayed the development of our proposals toward more transparent solutions that would not disturb the user experience. As a result, we obtained a secure system made of these tools and mechanisms that work together to provide full and transparent security for a digital documents management software. This security is fully based on cryptographic algorithms to provide provable and verifiable security properties. As a supporting layer for these mechanisms, a secure software library was designed to provide all the required tools for cryptographic uses in a portable way

Une multitude de systèmes de communication est aujourd'hui déployée sur l'ensemble du spectre radio, et l'attribution des radiofréquences est strictement régulée par des organismes internationaux. De fait, la bande passante attribuée aux réseaux cellulaires commerciaux est une ressource coûteuse et limitée. Les équipementiers et les opérateurs engagent des investissements considérables dans les infrastructures et le développement de ces réseaux cellulaires. Il est donc naturel qu'ils attachent une importance particulière aux problèmes de dimensionnement. Il est en effet indispensable de paramétrer au mieux ces systèmes pour un coût contrôlé, tout en leur garantissant les meilleures performances. Ce travail de thèse s'intéresse à l'étude de deux grandes technologies de réseaux de données cellulaires : les réseaux de deuxième génération (E)GPRS (2,5G) qui sont aujourd'hui largement utilisés dans le monde, et les réseaux WiMAX récemment intégrés dans les technologies de troisième génération (3G) et potentiellement les premiers réseaux de quatrième génération (4G). Pour ces deux technologies, nous proposons le développement de modèles analytiques simples et efficaces offrant des expressions à formes closes de tous les paramètres de performances du système. La vitesse d'exécution de ces modèles nous permet d'obtenir des résultats instantanés, en comparaison avec des simulations qui peuvent prendre de quelques minutes à plusieurs heures. Grâce à ces modèles, nous sommes capables de mener des études d'évaluation de performances complètes pour un nombre très important de configurations des paramètres du système et des paramètres de trafic. Enfin, la rapidité de résolution de ces modèles analytiques nous permet également de répondre à des problèmes complexes de dimensionnement qui seraient absolument inenvisageables à partir de simulations. Ces problèmes consistent par exemple à déterminer les valeurs optimales d'un ou plusieurs paramètres du système tout en garantissant des valeurs cibles sur les performances du réseau

La troisième génération de communications radio-mobile utilisera l'acces multiple à partition par code (code division multiple access). Les signaux envoyés sont actifs tout le temps et occupent la totalité de la bande fréquentielle allouée. Le code est constitué d'une séquence d'étalement (équivalent au codage à répétition permettant de supporter davantage de signaux) mélangée à une séquence de brouillage (permettant de séparer les signaux). Une détection conventionnelle est appliquée pour chaque signal. Dans un scenario plus élabore, une détection conjointe des utilisateurs peut être envisagée au niveau du récepteur, ceci constitue le thème principale de cette thèse. Dans notre modèle d'acces multiple, l'étalement est obtenu par un codage de canal. Le décodage se fait pour un seul signal à la fois, une estimation souple, basée sur les fiabilités, est retranchée du signal reçu. Le signal résultant est fourni aux autres décodeurs et la procédure d'élimination d'interference est itérée plusieurs fois. Les amplitudes des signaux et la variance du bruit blanc sont généralement inconnues à la réception. Nous proposons une méthode d'estimation basée sur l'algorithme expectation-maximization. Cette estimation est simple à implanter, elle est itérative et peut être réalisée en même temps que l'élimination d'interference, ce qui n'ajoute pas de retard supplémentaire. L'utilisation du turbo-code est justifié par l'augmentation du gain du codage. Nous proposons une turbo-code base sur des codes convolutifs super-orthogonaux à faible taux de codage. Deux critères sont donnes visant à mieux choisir les codes constituants du turbo-code. Afin de pouvoir les utiliser dans une application réelle, le décodage des turbo-codes est simplifie. Ceci mené à utiliser deux algorithmes de viterbi a fenêtre glissante. La complexité est énormément réduite ainsi que la taille des mémoires utilisées. Les simulations montrent que la dégradation des performances qui en résulte est inexistante sinon minime.

La mise en œuvre de systèmes basés OFDMA nécessite une synchronisation de la fréquence très fine en raison de l'extrême sensibilité de l'OFDMA aux décalages en fréquence porteuse (CFO). La synchronisation en fréquence devient plus difficile dans les systèmes OFDMA en liaison montante. Nos objectifs comprennent l'étude et l'analyse des problèmes résultant de décalages de fréquence et la proposition de solutions pour lutter contre ces problèmes. Nous examinons d'abord les interférences résultant de décalages de fréquence porteuse présents dans l'oscillateur du terminal utilisateur. Nous démontrons que l'on doit prendre en compte le préfixe cyclique tout en analysant les interférences résultant du CFO. Ensuite, nous montrons qu'il existe une contradiction entre la diversité de fréquence de canal et la robustesse contre le CFO. Nous proposons un compromis sous la forme d'une taille de bloc de seuil, afin de permettre un bon compromis entre la diversité des canaux et de robustesse pour les CFO pour le cas où aucune connaissances du canal n'est disponible. Quand le canal est connu, nous proposons une allocation optimale par bloc grâce à laquelle la robustesse aux CFO et à la diversité de fréquence de canal peut être réalisée en utilisant une petite taille de bloc petit pour des CFO de petite valeur. Nous proposons également une valeur CFO critique, en dessous de laquelle l'allocation optimal par bloc est très performant.Ensuite, nous proposons des solutions pour deux problèmes importants rencontrés dans un système OFDMA en liaison montante.Premièrement, nous proposons une méthode efficace pour l'estimation conjointe des réponses impulsionnelles des canaux et fréquences porteuses basée sur l'approximation polynomiale.Notre méthode d'estimation conjointe est plus simple que les méthodes existantes, sans aucune dégradation de performance. Ensuite, nous proposons une méthode de compensation de CFO basée sur l'annulation des interférences successives (SIC). La méthode d'annulation proposée réduit la complexité de mise en oeuvre quand le nombre de porteuses est important
One of the most prominent issues in the design and implementation of OFDMA based systems is the need for a very fine frequency synchronization due to the fact that OFDMA, like OFDM, is extremely sensitive to carrier frequency offsets (CFO). The task of frequency synchronization becomes more challenging in the uplink OFDMA-based systems where one OFDMA symbol is generated by the contribution of many different users. Our goals include the study and analysis of problems resulting from frequency mismatches provide solution to combat these problems. We first look at the interference resulting from CFOs, resulting from user terminal oscillator mismatch. We demonstrate that one must take into account the cyclic prefix while analyzing interference resulting from CFO. A new analytical expression of the ICI that takes into account the effect of CFO on the cyclic prefix is proposed. Then we focus our attention on analysis of the trade-off between channel frequency diversity and robustness against CFO and show that there exists a contradiction between the two. We propose a trade-off in the form of a Threshold blocksize, to allow a good compromise between the channel diversity and robustness for CFO for the case when no CSI is available. For system where CSI is available, we propose an optimal block carrier allocation scheme through which both robustness to CFO and channel frequency diversity can be achieved with small blocksize for small CFO. We also propose a Critical CFO value, above which the performance of the optimal block carrier allocation loses interest.Next we propose solutions for two important issues encountered in an uplink OFDMA system. First, we propose an efficient method for joint estimation of channel impulse responses and carrier frequency at the receiver based on polynomial approximation. Our proposed joint estimation method is simpler than the existing methods without any performance degradation. Next we propose a CFO compensation method based on successive interference cancellation. The proposed cancellation method reduces the implementation complexity faced in case of large DFT matrices