Browsing by Author "Abera, Mengistu"

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    Enhanced Peak-to-Average Power Ratio Reduction Technique In 0fdm Communication Systems
    (Addis Ababa University, 2007-06) Abera, Mengistu; Ayele, Hailu (PhD)
    The Orthogonal Frequency Division Multiplexing (OFDM) is a strong candidate for the current and future wireless communications system due to its high data rates transmission capability and robustness against multi-path fading effects. A major drawback of OFDM is its high peak to average power ratio (PAPR). Since most practical transmission systems are peak power limited, the average transmit power should be reduced for linear operation over the full dynamic range, which degrades the received signal power. In this thesis we review the most popular OFDM PAPR-reduction techniques and demonstrate in detail that Selected Mapping (SLM) scheme is a particularly promising reduction technique. In a SLM system, an OFDM symbol is mapped to a set of independent but equivalent symbols and then the lowest-PAPR symbol is selected for transmission. The tradeoff for PAPR reduction in SLM is computational complexity as each mapping requires an additional inverse fast Fourier transform (IFFT) operation in the transmitter. An enhanced SLM method is proposed for computational complexity reduction. The proposed SLM scheme transforms an input symbol sequence into a set of OFDM signals by multiplying the phase sequences by the signal after a certain intermediate stage of inverse fast Fourier transform (IFFT). The enhanced SLM technique reduces computational complexity by 48% while it shows almost the same performance of PAPR reduction as that of the conventional SLM OFDM scheme.
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    Project governance practices in Ethiopia: the case of Front-end project management practices in selected Government ministries
    (Addis Ababa University, 2018-06) Abera, Mengistu; Fanta, Tesgera (PhD)
    Project management success, achieving of the triple constraints, does not guarantee project success. More than 70% of projects fail or are challenged to achieve their planned objective (Standish Group, 2001). Thus, this raises the bigger question: is it morally, socially, economically and politically acceptable to decide funding of a project without figuring out whether the project can deliver the best service and with the most impact? Good project planning at the early stages of a project (the “front-end”) has been found to contribute significantly to the minimization of uncertainties, maximization of project benefits and thereby ensuring better opportunity for project success or reduce the ubiquitous problems that prevent the achievement of project success. The introduction and uses of front-end project management will be of critical importance for developing countries like Ethiopia in their selection of right projects and making an optimal decision only on projects that will have better impact for the social good. Accordingly, project governance practices in selected Ministries in Ethiopia have been explored in this study. A qualitative research design, with a case study methodology was used in the study; an in-depth interview of Directors and senior experts from four government ministries was considered as a data source. The ministry offices include Ministry of Finance and Economic Cooperation, Ministry of Communication and Information Technology, Ministry of Trade and National Planning Commission. A total of 12 senior executives and senior experts were interviewed on one-on-one basis. Thus, this study explored the front-end project management practices with regards to project definition and document preparation (presence of cost benefit analysis, benefit realization plan, organization change management and risk management plan), appraisal, and decision-making process in Ethiopia. Furthermore, the operating project management framework for achieving project success through the implementation of front-end project management for IT projects was explored. Accordingly, the study revealed that, the front-end planning is not adequately practiced. This was due to lack of personnel with the appropriate skills at different level, lack of clarity in mandates and of use of guidelines in the preparation and appraisal of public sector projects among others. The outcome of the study will be useful for the policy makers in pubic-sector IT projects front-end planning, in the determination of projects that can deliver the desired objective and support the senior management evidence based decision making process whether to approve, terminate, or modify projects.