ARJ  Volume 105 No 4

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1. Condition Monitoring of Medium Voltage Electrical Cables by Means of Partial Discharge Measurements

2. Requirements Practitioner Behaviour in Social Context: A Survey

3. A South African Perspective of the Requirements Discipline: An Industry Overview

4. A Framework for the Transmission of Multimedia Traffic Using HM and RS Nakagami-M Channels

5. Landmine Detection by Means of Ground Breaking Penetrating Radar: A Rule Based Approach

by H. van Jaarsveldt and R Gouws.

Abstract:The purpose of this paper is to discuss condition monitoring (CM) of medium voltage electrical cables by means of partial discharge (PD) measurements. Electrical cables are exposed to a variety of operational and environmental stressors. The stressors will lead to the degradation of the cable’s insulation material and ultimately to cable failure. The premature failure of cables can cause blackouts and will have a significant effect on the safety of such a network. It is therefore crucial to constantly monitor the condition of electrical cables. The first part of this paper is focussed on fundamental theory concepts regarding CM of electrical cables as well as PD. The derivation of mathematical models for the simulation of PD is also discussed. The simulation of discharge activity is due to a single void within the insulation material of medium voltage cross-linked polyethylene (XLPE) cables. The simulations were performed in the MATLAB® Simulink® environment, in order to investigate the effects of a variety of parameters on the characteristics of the PD signal. A nonintrusive CM technique was designed for the detection of PD activity within cables. The CM technique was used to measure and analyse practical PD data. Two MATLAB® programs were designed to analyse the PD data in both the time-domain and frequency-domain.
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by A. Marnewick, JHC Pretorius and L Pretorius.

Abstract: The purpose of this research paper is to discover the social behaviour of practitioners that causes the communication breakdowns during the requirements engineering process. Requirements emerge from the social interaction and communication between the requirements practitioner and the various stakeholders. The main problems with the requirements engineering process are communication and coordination breakdowns, as well as the lack of domain knowledge or understanding of the problem. These challenges are all related to the social interaction during the requirements engineering process that impacts the quality of requirements. In practice, requirements are still produced with errors which then lead to unsuccessful solutions to problems. The ultimate goal of any practitioner is delivering a solution fit for purpose first time around. If the social patterns of practitioners that deliver quality requirements are known and compared with those that do not deliver quality requirements, individual performance can be adjusted. The results of this study confirmed that quality of requirements is dependent on the communication established between the requirements practitioner and relevant stakeholders. The communication is enabled through the trust relationships between the parties. A description of how practitioners behave during the requirements process is provided. By discovering these interaction patterns, communication can be improved and made more effective. Additionally, the relationships between the practitioners and their stakeholders are described. These trust patterns provide insight into the levels of collaboration, communication and sharing of knowledge between the practitioners and their stakeholders. By identifying these relationship patterns, the value each party receives from the relationships could increase, and the communication breakdowns could be minimised.
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by M.B. Balogun, O.O. Oyerinde and S. H Mneney

Abstract: The recently proposed Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) scheme has been at the forefront of wireless communication systems research due to its promising features which include high efficiency, flexibility and high data-rate wireless transmission. Earlier, major research on this new scheme had only focused on the perfect-condition scenarios, with the assumption that the system is free from synchronization errors. However, recent studies show that synchronization errors, especially the carrier frequency offsets, have significant impact on the OFDM-IDMA systems. This work therefore examines comprehensively, analyses and verifies the impact of synchronization errors on the performance of the OFDM-IDMA hybrid multicarrier scheme. Furthermore, simple but effective synchronization algorithms, namely; the linear minimum mean-squared error (MMSE) based algorithm, and the Kernel Least Mean Square (KLMS) algorithm as well as its normalized counterpart called the Normalized-KLMS are adopted and adequately exploited to combat the degrading impacts of synchronization errors on the OFDM-IDMA scheme. The linear minimum mean-squared error (MMSE) based algorithm, is a non-data aided method, which focuses on the mitigation of the interchannel interference induced by the effect of synchronization errors on the system. The Kernel Least Mean Square (KLMS) algorithm, as well as its normalized counterpart, presents an efficient approach for estimation and effective correction methods to combat the effect of carrier frequency offset errors
on the performance of the OFDM-IDMA system. The bit error rate (BER) performance of these algorithms is presented, compared, and analyzed. Also, the achievable performance of these synchronization algorithms in a Rayleigh multipath channel scenario with varying mobile speed is analyzed and documented.

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by T. Quazi, H. Xu and A Saeed

Abstract: Hierarchical modulation (HM) provides different levels of error performance for the high and low priority bits modulated. This differentiation can be aligned to various classes of multimedia traffic demanding different levels of error rate performance. In a previous cross-layer design scheme, which combined conventional modulation at physical layer with RS coding at the application layer, an unequal error protection mechanism was used at the application layer for guaranteeing quality of service for various classes of multimedia traffic. Instead of using only a single layer, in this paper we present a more flexible two layer cross-layer design framework for unequal error protection, combining RS coding at the application layer with HM at the physical layer. Furthermore, in order to improve error performance of the system, a signal space diversity (SSD) scheme is also incorporated into the physical layer of the framework. Without consuming additional transmit power and bandwidth, the use of the SSD HM in the cross-layer design system resulted in significant gains when compared to the non-SSD, standard HM system. It is shown that the cross-layer design system with SSD HM has a 10dB gain over the non-SSD HM system in a Nakagami m=1 channel with a frameerror rate target of 10-4.
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by P.A van Vuuren

Abstract: For a humanitarian landmine detection system to be of practical value it has to meet the following criteria: detection must be performed in real-time from a moving platform; plastic mines must be reliably detected; and the false alarm rate should be kept to a minimum Ground penetrating radar is a promising technology for the detection of landmines with low metal content. The improved algorithms presented in this paper can meet the above mentioned criteria to a large extent. Clutter removal is performed by an adaptive filter which removes virtually all background clutter in real time and can adapt to changing soil characteristics. Classification is performed by a new rule-based classifier capable of detecting both metal and plastic anti-tank mines. Despite the fact that the algorithms are currently implemented in Matlab, mine detection can be performed on a vehicle moving at 9 km/h.
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