Scielo RSS <![CDATA[SAIEE Africa Research Journal]]> http://www.scielo.org.za/rss.php?pid=1991-169620190004&lang=pt vol. 110 num. 4 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Simplified ML-Based Carrier Frequency Offset and Phase Noise Estimation for CO-OFDM Systems</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000400001&lng=pt&nrm=iso&tlng=pt The coherent optical orthogonal frequency division multiplexing (CO-OFDM) has become prominent among emerging telecommunication techniques and applications. However, carrier frequency offset (CFO) and laser phase noise adversely impact and degrade the performance of the CO-OFDM systems. In this paper, a simplified maximum-likelihood (ML) approach, which eliminates the need for the exhaustive search associated with traditional ML methods, is derived and utilized for the estimation of CFO and laser phase noise in CO-OFDM systems. Furthermore, to obtain an improved performance, the proposed simplified low-complexity ML estimator is uniquely combined with an efficient data-dependent pilot-aided (DD-PA) technique, for the acquisition of both the CFO and the laser phase noise. The performance of the simplified ML-based estimators is compared with existing methods and verified in a 16-ary quadrature amplitude modulation (16-QAM) CO-OFDM system with polarization mode dispersion (PMD), chromatic dispersion (CD) and other polarization dependent losses (PDLs) along the fiber link. <![CDATA[<b>Rope-Weaver's Principles</b>: <b>Towards More Effective Learning</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000400002&lng=pt&nrm=iso&tlng=pt This paper introduces a new methodology to assist teaching and learning in a time-constrained environment at the hand of two time-on-task examples. These examples are from the field of Electrical Engineering studies with a focus on first-year studies and an advanced software design course taught at the Tshwane University of Technology in South Africa. In an endeavour to understand the timing model of the human brain to master and assimilate new information, a study was conducted to determine some of the parameters that could possibly have an influence on the timing model and how the brain perceives new information. From this study the Rope-Weaver's Principles were derived and are built on three well-known theories, comparative judgment, the Guttman scale and the learning curve, integrated into the new methodology. The Rope-Weaver's Principles are presented as an abstraction of the mathematical principles and the measures that underpin this study. The research was done from a participant-observer perspective with design research as central methodology. The research methodology involved a longitudinal study employing mixed-methods research. The results led to the observation of a toe or plateau in the infancy of the learning curve. The observed plateau has a direct influence on the order and time frame of the introduction of new study material in a formal educational programme. The results were found to adhere to the Weber-Fechner Law. This relates to other studies on animals, suggesting that the way the brain perceives stimuli or assimilate knowledge is hard-wired throughout the animal kingdom although the brain structures vary widely. It is proposed that Rope-Weaver's Principles, complementary to the current pool of teaching and learning theories, lead to a better mastery of the learning material or skills, moving persons under instruction from rule based training - behaviourism, to maxim integration - constructivism. <![CDATA[<b>An Alternative technique for the detection and mitigation of electricity theft in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000400003&lng=pt&nrm=iso&tlng=pt Electricity theft and illegal connection by ground surface conductors is a pervasive problem in South Africa. The impact this phenomenon has is not only limited to revenue loss and equipment damage, but also presents a life threatening hazard. Although the issues of non-technical losses have been researched for decades, no universal solution has been presented, due to the complexity of the problem. This paper investigates the application of zero-sequence current-based detection as a mitigation strategy to deal with illegal connections by ground surface conductors. Simulation and experimental results show the validity of this technique as well as its dependence on seasonal change of the soil resistivity.