ARJ Volume 106 No 4
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Table of Contents (1.91 MB)
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1. A Measurement System to Record the ULF Electric Fields Related to the Elasmobranch Electrosensory System.
2. Investigation into the Role of Singlet Oxygen in Positive Corona in Air.
3. Space-time Precoded CDMA-OFDMA Employing Super-Orthogonal Complete Complementary Codes.
4. Symbol Error Rate of Generalised Selection Combining with Signal Space Diversity in Rayleigh Fading Channels.
5. Performance of Local Averaging Handover Technique in Long Term Evolution Networks.
A Measurement System to Record the ULF Electric Fields Related to the Elasmobranch Electrosensory System
by G.J. Gibbon
Abstract: Numerous observations and reports indicate that sharks are often attracted to, or repelled by, the Electromagnetic (EM) Radiation from underwater electrical apparatus and man-made installations resulting in damage to the equipment and possible ecological damage. It is essential that, with the introduction of more and more man-made underwater devices, a study of “normal” electric activity in the oceans is made so this can be compared with possible increased activity from man-made systems. In this paper the development, design and implementation of an underwater electric field recorder that can be towed by a scuba diver is presented. The measurement system uses carbon fibre probes to measure three channels in the frequency range of 0.1 - 10 Hz at 64 samples/sec with a resolution of 24 bits. The input range is ±18 mV/m with a noise floor of less than ±30 μV/m. The system can record for up to one hour and the measurements are downloaded to a computer for analysis.
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Investigation into the Role of Singlet Oxygen in Positive Corona in Air
by A.G. Swanson and I.R. Jandrell
Abstract: Corona is the partial breakdown of air in a divergent electric field and is particularly evident around high voltage equipment. Air comprises of nitrogen and oxygen and the corona process involves many complex phenomena including ionisation, attachment and excitation and the interaction of the ions and excited molecules generated by these phenomena. A particular state of excited molecular oxygen, singlet oxygen, has the characteristic that it remains excited for a relatively long period oftime. Singlet oxygen plays a role in the detachment of electrons from the negative oxygen ions and its role in corona discharges has been accounted for through theory and models, but due to the difficulties of measurement of the singlet oxygen, the influence it does have on corona discharges is not entirely clear. On this basis the gas processes associated with the corona discharge in air have been explored, where a Boltzmann equation solver, the electron energy distribution function, transport coefficient and Townsend coefficients are used to understand the phenomena and provide input to a gas discharge model, where the gases are representing as species in a drift-diffusion model. The model indicates the presence of negative ions and singlet oxygen, but clearly illustrates how the space charge plays the critical role in positive corona due to the collapse of the electric field. An experiment that involved altering the environment with air-flow produced an unexpected result in the positive onset streamers where the repetition rate changed considerably, initially it was thought that this was due to the removal of singlet oxygen. In an effort to determine if their was a relationship between repetition rate and singlet oxygen, experiments detecting the emission from singlet oxygen and exciting oxygen through a laser were undertaken. There was no evidence to suggest that the repetition rate of the positive onset streamers could be related to singlet oxygen. There were no emissions detected from various configurations, whilst visible corona was clearly seen. The experiment where laser induced excitation showed no change in repetition rate. It could be inferred that a relationship between repetition rate and that the detachment due to negative ions and singlet oxygen is not a dominant process in the corona discharge.
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Space-time Precoded CDMA-OFDMA Employing Super-Orthogonal Complete Complementary Codes
by N. de Figueiredo, L.P. Linde and J.H. van Wyk
Abstract: IThis paper addresses and illustrates, both analytically as well as by means of simulation, the equivalence of a cyclically rotated complete complementary coded (CRCCC) code division multiple access orthogonal frequency division multiplexed (CDMA-OFDM) BPSK/QPSK system and a narrowband uncoded BPSK/QPSK reference system. The equivalence can be attributed to the MUI-free characteristic performance of CRCCCs. It is demonstrated that when employed in a multiple-input multiple-output (MIMO) antenna configuration along with orthogonal space-time block codes (OSTBCs), the maximum theoretical diversity order of NTxNRx is achieved. Most significantly, simulations show that CDMA-OFDM using CRCCCs is capable of rendering additional multipath diversity gain at no additional processing cost. This signifies improved performance when compared with conventional ST-OFDM systems.
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Symbol Error Rate of Generalised Selection Combining with Signal Space Diversity in Rayleigh Fading Channels
by A. Essop and H. Xu
Abstract: This paper concerns M-ary quadrature amplitude modulation (M-QAM) with signal space diversity (SSD) and generalised selection combining (GSC) in independent and identically distributed (i.i.d) Rayleigh fading channels. The theoretical symbol error rate (SER) performance in i.i.d Rayleigh fading channels for M-QAM with SSD and GSC is derived. The theoretical SER performance of M-QAM with SSD and GSC reception is confirmed via simulations. Thereafter, the diversity gain of M-QAM with SSD and GSC is also analysed. Finally the signal-to-noise ratio (SNR) gap of M-QAM with SSD between selection combining (SC) and maximal ratio combining (MRC) is investigated and validated via simulations.
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Performance of Local Averaging Handover Technique in Long Term Evolution Networks
by I.O. Elujide, O.O. Olugbara, P.A. Owolawi and T. Nepal
Abstract: In this paper, we investigate the performance of an alternative received signal filtering technique based on local averaging to improve the quality of handover decisions in Long Term Evolution (LTE) networks. The focus of LTE-Advance (LTE-A) networks is to provide enhanced capacity and reliability of radio access as well as broadband demand for mobile users. The necessity to maintain quality of service, especially for the delay sensitive data services and applications, has made mobility and handover decisions between the base stations in the LTE networks critical. Unfortunately, several handover decision algorithms in the LTE networks are based on the Reference Signal Received Power (RSRP) obtained as a linear averaging over the reference signals. The critical challenge with the linear averaging technique is that the limited reference signal available in the downlink packet introduces an estimation error. This estimation error is a result of the effects of linear averaging on propagation loss components in eliminating fast-fading from the received signals. Moreover, prompt and precise handover decisions cannot be based on inaccurate measurement. The standardized LTE layer 3 filtering technique is applied to the local averaged layer 1 signal to render it suitable for LTE handover decisions. The local averaging technique produces better handover than the linear averaging technique in terms of the reduced number of handover failures, improved high spectral efficiency and increased throughput, especially for cell-edge users with high speeds. The findings of this study suggest that the local averaging technique enhances mobility performance of LTE-Advance networks.
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