ARJ  Volume 106 No 3

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Table of Contents (2.11 MB)

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1. Teletraffic Analysis of a Call Admission Control Scheme with TCP Protocol Induced.

2.  A Study on Impulse Noise and Its Models.

3. Development of a Maintenance Strategy for Power Generation Plants.

4. Model Predictive Control of an Active Magnetic Bearing Suspended Flywheel Energy

5. Incentives and South Africa’s Automotive Industry Performance: A System Dynamics Approach.

6. Analysis and Optimization of Auto-Correlation Based Frequency Offset Estimation

Teletraffic Analysis of a Call Admission Control Scheme with TCP Protocol Induced.
by T Walingo

Abstract: Future networks face tremendous challenges towards providing guaranteed Quality of Service (QoS) for the multiple traffic types employing numerous protocols. This work presents an expanded parameter Call Admission Control (CAC) scheme and intelligent scheduling to provide QoS on modern networks. The expanded parameter CAC scheme features the lower layers Signal to Interference Ratio (SIR) and network delay as admission parameters. The SIR is due to the transmission on the code division multiple access network and delay is due to the operation of the Transmission Control Protocol (TCP). TCP delay is a good representative of the aggregated delays of the entire network; both access and core network as it is at a higher layer. TCP was ideally designed for wired networks. TCP performance is degraded and leads to substantial delay while operating on wireless lossy links as it reduces the sending rate and resends lost packets. This work presents an analytical framework for evaluating the performance of a wireless TCP based CAC model which features Batch Markovian Arrival Process(BMAP) traffic, a better representative of the future traffic characteristics than the traditional Poisson traffic. A teletraffic analysis of a network with TCP is done and the impact of TCP induced delays on the network is investigated for a future generation CAC scheme.
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A Study on Impulse Noise and Its Models
by T. Shongwe  and A. J. Han Vinck  and H. C. Ferreira

Abstract: This article gives an overview of impulse noise and its models, and points out some important and interesting facts about the study of impulse noise which are sometimes overlooked or not well understood. We discuss the different impulse noise models in the literature, focusing on their similarities and differences when applied in communications systems. The impulse noise models discussed are memoryless (Middleton Class A, Bernoulli-Gaussian and Symmetric alpha-stable), and with memory (Markov-Middleton and Markov-Gaussian). We then go further to give performance comparisons in terms of bit error rates for some of the variants of impulse noise models. We also compare the bit error rate performance of Single-Carrier (SC) and Multi-Carrier (MC) communications systems operating under impulse noise. It can be seen that MC is not always better than SC under impulse noise. Lastly, the known impulse noise mitigation schemes (clipping/nulling using thresholds, iterative based and error control coding methods) are discussed.
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Development of a Maintenance Strategy for Power Generation Plants
by L. Ndjenja and J.K. Visser.

Abstract: Effective maintenance of power generation systems is essential to ensure that the variable demand for electricity is satisfied on a daily basis. Equipment used on generation plants, e.g. boilers, turbines, generators, compressors and pumps, are becoming more sophisticated and complex, and therefore require more effective maintenance strategies and tactics. A number of maintenance  approaches have been developed in the last 4-5 decades, e.g. reliability-centred maintenance, business-centred maintenance, and total productive maintenance. This paper discusses the results of a research study done to investigate strategy in the maintenance environment of power generation systems. The study found that most power stations have a maintenance strategy and use maintenance approaches and different maintenance tactics like run-to-failure, time-based maintenance and condition-based maintenance. It was also found that the SAPTM information system is used by nearly all power stations.
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Model Predictive Control of an Active Magnetic Bearing Suspended Flywheel Energy
by K.R. Uren, G. van Schoor and C.D. Aucamp.

Abstract: Flywheel Energy Storage (FES) is rapidly becoming an attractive enabling technology in power systems requiring energy storage. This is mainly due to the rapid advances made in Active Magnetic Bearing (AMB) technology. The use of AMBs in FES systems results in a drastic increase in their efficiency. Another key component of a flywheel system is the control strategy. In the past, decentralised control strategies implementing PID control, proved very effective and robust. In this paper, the performance of an advanced centralised control strategy namely, Model Predictive Control (MPC) is investigated. It is an optimal Multiple-Input and Multiple-Output (MIMO) control strategy that utilises a system model and an optimisation algorithm to determine the optimal control law. A first principle state space model is derived for the purpose of the MPC control strategy. The designed MPC controller is evaluated both in simulation and experimentally at a low operating speed as a proof of concept. The experimental and simulated results are compared by means of a sensitivity analysis. The controller showed good performance, however further improvements need to be made in order to sustain good performance and stability at higher speeds. In this paper advantages of incorporating a system model in a model-based strategy such as MPC are illustrated. MPC also allows for incorporating system and control constraints into the control methodology allowing for better efficiency and reliability capabilities.
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Incentives and South Africa’s Automotive Industry Performance: A System Dynamics Approach
by M. Kaggwa and J. L. Steyn.

Abstract: Investment in robotic automotive manufacturing and inherent electronics has played apivotal role in the growth and competitiveness of the South African automotive industry. Government's offering of incentives was intended to lessen the cost of local industry’s expensive, but necessary investment. Despite the growth, industry trade balance has been declining systematically. To explain the apparent contradiction in industry performance, a model of South Africa’s automotive incentives – including the Productive Asset Allowance (PAA) and the Import-Export Complementation (IEC) – was developed. Model simulations reveal that, while the IEC had a significant effect on the industry trade balance, the role of the PAA in this regard is trivial. Ultimately, the study reveals that combining strictly investment incentives with other non-investment’ incentives can have unintended consequences for the local automotive industry.
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Analysis and Optimization of Auto-Correlation Based Frequency Offset Estimation
by I.M. Ngebani , J.M. Chuma and S. Masupe.

Abstract: In this letter, a general auto-correlation based Frequency Offset Estimation (FOE) algorithmis analyzed. An approximate closed-form expression for the Mean Square Error (MSE) of the FOE is obtained, and it is proved that, given training symbols of fixed length N, choosing the number of summations in the auto-correlation to be N3  and the correlation distance to be 2N 3  is optimal in that it minimizes the MSE. Simulation results are provided to validate the analysis and optimization.
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