ARJ  Volume 107 No 1

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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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