2008: Vol 99 No 3

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1. A novel uniplanar electromagnetic bandgap unit Cell design with reduced spurious radiation
2. A study of the effect of MPLS on quality of service in wireless LANs
3. Effective earth radius factor measurement and modelling for radio link design in Botswana
4. Development of a Mathematical Model for Reactive Power Transmission Costs in Electric Power Systems

A novel uniplanar electromagnetic bandgap unit Cell design with reduced spurious radiation by E. Laubscher and R.H. Geschke
Abstract: We present a novel electromagnetic bandgap structure with reduced spurious radiation properties. The application presented here is the wide-band suppression of parasitic parallel-plate modes on multilayer printed circuit boards. We use a well known unit-cell design as a benchmark for the new structure. Two optimized configurations highlight unit cell design aspects.
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A study of the effect of MPLS on quality of service in wireless LANs by J. Schutte and A.S.J. Helberg
Abstract: The increasing deployment and availability of wireless technology presents unique research challenges, especially in the field of Quality of Service. The IEEE 802.11 wireless Local Area Network standard is the most popular standard currently in use, but is unable to provide Quality of Service guarantees for the growing number of wireless real-time and multimedia applications. Quality of Service provision is made more difficult in a wireless network due to the lossy physical medium and the limited resources available. Also, wired internet protocol Quality of Service mechanisms such as Differentiated Services do not always perform well in a wireless environment. In this study, we evaluate the use of Multi-Protocol Label Switching as a means of adding Quality of Service to a wired backbone with limited bandwidth, connected to a wireless Local Area Network. We compare the performance of Multi-Protocol Label Switching Traffic Engineering with that of Differentiated Services, and show that Multi-Protocol Label Switching Traffic Engineering is able to effectively share the available resources among all traffic types.
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Effective earth radius factor measurement and modeling for radio link design in Botswana by T.J. Afullo and P.K. Odedina
Abstract: In this presentation, we present models for determining the probability density function (pdf) of the effective earth radius factor for Botswana as a means of predicting the k-factor variation. The models are based on the radiosonde measurement data obtained in earlier reports. The first model, which is a curve-fitting one, is based on the bell-shaped variation of the plotted k-factor; it uses the integral of square error (ISE) comparison between f(k) (the measured pdf), and f*(k) (the modeled estimation of the pdf) to obtain the best approximation of f(k). We use f(k) to determine both the median of k and the value of k exceeded 99.9% of the time, for the height ranges 0-200 m and 0-500 m above ground level. It is observed that at both height spans of 0-200 m and 0-500 m a.g.l., the all-year median value of k, ??k, is 1.12 for the curve-fitting model. The second model uses the kernel estimate for the pdf, with a focus on three kernels – the biweight kernel, the triangular kernel, and the Gaussian kernel. We again compare the kernels using the ISE criterion. The kernel model indicates that, for 0-200m height range, the median value of k varies between 1.11 and 1.13, with the highest variation arising from the Gaussian kernel, and lowest from the biweight kernel. On the other hand, for the 0-500m range, the median value of k is 1.09. It is found that the biweight kernel gives the best estimate of f(k) for the optimum window width of 0.25.
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Development of a Mathematical Model for Reactive Power Transmission Costs in Electric Power Systems by G.O. Anderson
Abstract: The paper gives detailed analyses to help determine the increase in production costs due to the transmission of reactive power. On the basis of that and with due consideration to the cost of VARS compensation equipment, a mathematical model is developed to determine an economically justified transmission distance for VARS in electric power systems. Standard voltages and line parameters are used for the computations. MATLAB computer programming is used to obtain the numerical results. The developed mathematical model and the numerical results could be useful to electric power systems engineers.
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