ARJ Volume 107 No 1
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Table of Contents (237 KB)
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1. Modernising, Upgrading and Recommissioning the Indoor Antenna Range at Stellenbosch University
2. 30-Second and One-Minute Rainfall Rate Modelling and Conversion for Millimetric Wave Propagation in South Africa
3. Log-domain Interactive Sphere Decoder with Symbol Sorting
4. A Framework for the Transmission of Multimedia Traffic Using HM and RS Nakagami-M Channels
MODERNISING, UPGRADING AND RECOMMISSIONING THE INDOOR ANTENNA RANGE AT STELLENBOSCH UNIVERSITY
by D. M. P. Smith, D. B. Davidson, A. Bester and J. Andriambeloson
Abstract:
This paper describes the upgrade to the indoor antenna range at Stellenbosch University. The previous measurement process relied
upon obsolescent control equipment and undocumented software; it was critical that these be replaced. Now, the antenna range supports
three measurement types using a commercial integrated measurement control system that provides support for high gain and low gain antennas
over a wide frequency range. These are spherical near-field, planar near-field and conventional far-field measurements, with the potential
to implement cylindrical near-field. The antenna range potentially supports operations from 1 GHz up to 26.5 GHz, though the currently available
probes do not cover the full band. The main physical upgrad was performed during October 2014, though investigations had already begun in 2011,
and some supplementary tasks were still ongoing at the time of writing.Several innovative commissioning tests have been undertaken,
some of which are only possible with near-field metrology, and these are described in the paper.
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30-Second and One-Minute Rainfall Rate Modelling and Conversion for Millimetric Wave Propagation in South Africa
by M. N. Ahuna, T. J. Afullo and A.A. Alonge
Abstract: The knowledge of adequate rainfall statistics will contribute greatly to the roll-out of emerging wireless technologies
on the platform of Long-Term Evolution (LTE) and WiMax (IEEE 802.16). Therefore, it is important that rainfall measurements at shorter
integration time are incorporated as useful inputs in the planning of Line-of-Sight (LOS) microwave and millimetre
communication links for hosting these technologies. As compared to the use of one-minute rainfalldata as suggested by
International Telecommunication Union (ITU), the equivalent data measured at 30-second interval gives more information of temporal
rain rates in the time domain. Therefore, in this study, rainfall rate measurements of 5-minute integration time representative of 10
locations in South Africa are evaluated to obtain their cumulative distributions. Results from these analyses are compared with rainfall
data of one-minute and 30-second integration time data obtained over Durban (29?52’E, 30?55’S), South Africa. Consequently,
rainfall rate models for conversion to one-minute and 30-second integration times were obtained over 10 locations in South Africa using the power-law
regression functions. Our results obtained over these locations were used to estimate specific attenuation values in selected microwave and millimetric
wave bands at 12 GHz, 30 GHz and 60 GHz for 10 locations under study. It is confirmed that the 30-second integration time provides more
information needed for estimation of specific attenuation on microwave and millimeter-wave radio links in South Africa.
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Log-domain Interactive Sphere Decoder with Symbol Sorting
by P. R. Botha and B. T. J. (Sunil) Maharaj
Abstract: In this paper the authors propose modified branch and pruning metrics for the sphere decoder
to facilitate the use of apriori information in the sphere decoder. The proposed sphere decoder operates
completely in the log-domain. Additionally the effect of order in which the symbols are decoded on the
computational requirements of the decoder are investigated with the authors proposing a modification
of the sorted QR decomposition (SQRD) algorithm to incorporate apriori information. The modified
SQRD algorithm is shown to reduce the average number of computations by up to 95%. The apriori
sphere decoder is tested in an iterative multiple input multiple output (MIMO) decoder and shown
to reduce the bit error rate (BER) by an order of magnitude or provide approximately a one decibel
improvement
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Effect of Surface Discharges on Lightning Impulse Breakdown Voltage of Oil-Impregnated Pressboard in Power Transformers
by M. M. Tshivhilinge and C. Nyamupangedengu
Abstract: Power transformers inevitably experience impulse over-voltage stresses such as from lightning and/or switching events despite various protection systems that may be in place.
At locations along oil/pressboard interfaces in the transformer, surface discharges may initiate due to various reasons. The surface discharges may or may not eventually lead to voltage flashover faults.
This paper presents a study of how relatively small surface discharges affect the lightning voltage impulse (LI) strength of oil-impregnated pressboard insulation. It is found that surface discharges of
magnitudes in the order of some hundreds of pC can reduce the LI withstand voltage of the oilimpregnated pressboard by up to 15%. Although the negative polarity LI withstand voltage of surface
discharge-aged pressboard is higher than that of positive polarity, the reduction in the LI voltage strength is more pronounced for the negative LI impulse voltage. The findings suggest further
scrutiny of the standardised acceptable levels of PD in power transformers
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