Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736911
G. Saban, R. Braun
In developing countries there is an increasing demand for telecommunications and Internet access. The current problem, especially in Africa, is to find solutions which can provide under developed countries with a satisfactory network. This requires a relatively fast roll-out at low-cost. Modern wireless systems claim to offer quick and easy deployment. However, in many cases the wireless system deployment is delayed because adequate radio plans have to be designed, and they are not optimized for Internet and computer communications. Multihop packet radio can offer computer communication in an easily deployable ad-hoc wireless network which does not require frequency planning. However, voice traffic is not easily implemented on packet radio networks due to the bursty and delayed traffic characteristics. A multihop packer radio network is proposed which offers voice and Internet communications.
{"title":"Wireless local loop and packet radio technology for developing communities","authors":"G. Saban, R. Braun","doi":"10.1109/COMSIG.1998.736911","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736911","url":null,"abstract":"In developing countries there is an increasing demand for telecommunications and Internet access. The current problem, especially in Africa, is to find solutions which can provide under developed countries with a satisfactory network. This requires a relatively fast roll-out at low-cost. Modern wireless systems claim to offer quick and easy deployment. However, in many cases the wireless system deployment is delayed because adequate radio plans have to be designed, and they are not optimized for Internet and computer communications. Multihop packet radio can offer computer communication in an easily deployable ad-hoc wireless network which does not require frequency planning. However, voice traffic is not easily implemented on packet radio networks due to the bursty and delayed traffic characteristics. A multihop packer radio network is proposed which offers voice and Internet communications.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"113 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122460631","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736958
W. Nel, G. de Jager
Designers of classifiers are faced with the problem of deciding which features should be used when building classifiers. The notion that adding extra features will always improve a classifier has been proved to be incorrect in the past. Thus, it is necessary to also investigate subsets of the full extracted feature set, to see whether better classification would not result. This feature input reduction also has an effect on cost and speed. Three methods for doing this input reduction are evaluated and compared. The methods yield encouraging results on real data sets. It is found that the gamma test method also has high correlation with classifier error rates, which might have a high impact on stopping criteria for neural networks.
{"title":"The search for more optimal input spaces","authors":"W. Nel, G. de Jager","doi":"10.1109/COMSIG.1998.736958","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736958","url":null,"abstract":"Designers of classifiers are faced with the problem of deciding which features should be used when building classifiers. The notion that adding extra features will always improve a classifier has been proved to be incorrect in the past. Thus, it is necessary to also investigate subsets of the full extracted feature set, to see whether better classification would not result. This feature input reduction also has an effect on cost and speed. Three methods for doing this input reduction are evaluated and compared. The methods yield encouraging results on real data sets. It is found that the gamma test method also has high correlation with classifier error rates, which might have a high impact on stopping criteria for neural networks.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126872237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736972
P. Pretorius, A. Britten, J. Van Coller, J. Reynders
The potential threat that electromagnetic disturbances generated during disconnector switching poses to substation-based control, protection and communication equipment has been raised in previously published literature. A better understanding of the coupling mechanisms involved can assist engineers in designing systems that are immune to these disturbances. An experiment designed to evaluate inductive, capacitive and conductive interference in the context of coupled unwanted common mode currents is described.
{"title":"Evaluation of the coupling mechanisms of electromagnetic disturbances resulting from disconnector switching in substations: experimental design and initial results","authors":"P. Pretorius, A. Britten, J. Van Coller, J. Reynders","doi":"10.1109/COMSIG.1998.736972","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736972","url":null,"abstract":"The potential threat that electromagnetic disturbances generated during disconnector switching poses to substation-based control, protection and communication equipment has been raised in previously published literature. A better understanding of the coupling mechanisms involved can assist engineers in designing systems that are immune to these disturbances. An experiment designed to evaluate inductive, capacitive and conductive interference in the context of coupled unwanted common mode currents is described.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"495 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115882420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736997
D. Davidson, I. Theron, U. Jakobus, F. Landstorfer, F. Meyer, J. Mostert, J. V. van Tonder
This paper describes recent progress with FEKO, an antenna simulation program. FEKO uses the method of moments (MoM), and also offers users a hybrid MoM/physical optics for suitable electrically large problems. Current work on UTD hybridisation is outlined, as well as work on the pre- and post-processors. The performance of FEKO in high-performance computing environments is discussed. The incorporation of a rigorous stratified media treatment is reviewed and current plans for FEM hybridisation briefly outlined.
{"title":"Recent progress on the antenna simulation program FEKO","authors":"D. Davidson, I. Theron, U. Jakobus, F. Landstorfer, F. Meyer, J. Mostert, J. V. van Tonder","doi":"10.1109/COMSIG.1998.736997","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736997","url":null,"abstract":"This paper describes recent progress with FEKO, an antenna simulation program. FEKO uses the method of moments (MoM), and also offers users a hybrid MoM/physical optics for suitable electrically large problems. Current work on UTD hybridisation is outlined, as well as work on the pre- and post-processors. The performance of FEKO in high-performance computing environments is discussed. The incorporation of a rigorous stratified media treatment is reviewed and current plans for FEM hybridisation briefly outlined.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115940598","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.737002
P. Meyer
A novel analysis technique based on the method-of-lines and mode-matching is used for investigating the distribution and amplitudes of higher-order modes at any plane inside microstrip structures. The fundamentally ill-conditioned problem of transforming high order mode amplitudes across two-port networks is eliminated by following an approach similar to circuit based nodal analysis. An interdigital filter is presented as a case study.
{"title":"Techniques for investigating higher-order mode interaction inside microstrip circuits","authors":"P. Meyer","doi":"10.1109/COMSIG.1998.737002","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.737002","url":null,"abstract":"A novel analysis technique based on the method-of-lines and mode-matching is used for investigating the distribution and amplitudes of higher-order modes at any plane inside microstrip structures. The fundamentally ill-conditioned problem of transforming high order mode amplitudes across two-port networks is eliminated by following an approach similar to circuit based nodal analysis. An interdigital filter is presented as a case study.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123289445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.737004
G. Farquharson, A. Langman, M.R. Inngs
With the advent of cheaper, RF integrated circuit devices, it has now becoming feasible to build portable stepped frequency, ground penetrating radars based on heterodyne architectures. These overcome the problems encountered in the homodyne systems, and the performance limiting factors that do exist, are able to be more effectively controlled. This paper presents the design of a 50-800 MHz stepped frequency continuous wave ground penetrating radar based on a heterodyne architecture. It discusses architectural benefits of heterodyne receivers, the implementation of the stepped frequency synthesizers and transceiver and presents performance predictions for the system.
{"title":"A 50-800 MHz stepped frequency continuous wave ground penetrating radar","authors":"G. Farquharson, A. Langman, M.R. Inngs","doi":"10.1109/COMSIG.1998.737004","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.737004","url":null,"abstract":"With the advent of cheaper, RF integrated circuit devices, it has now becoming feasible to build portable stepped frequency, ground penetrating radars based on heterodyne architectures. These overcome the problems encountered in the homodyne systems, and the performance limiting factors that do exist, are able to be more effectively controlled. This paper presents the design of a 50-800 MHz stepped frequency continuous wave ground penetrating radar based on a heterodyne architecture. It discusses architectural benefits of heterodyne receivers, the implementation of the stepped frequency synthesizers and transceiver and presents performance predictions for the system.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125383829","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736965
J. Hattingh
The CE directives on EMC which came into effect on 1st January 1996, have led to an increasing awareness of the uncertainty of measurements in radiated emissions. EMC antenna calibration, and open area test site (OATS) validation, are two of the topics which now feature prominently in virtually any discussion on the subject of EMC. The South African Bureau of Standards constructed a new OATS in 1993, and the validation of this site was followed by a number of antenna intercomparison exercises. An application for accreditation by the National Laboratory Accreditation Service (NLA) was submitted early in 1998, and the assessment took place on 15 April 1998. This paper will deal primarily with the process which was followed to put the theoretical concepts behind OATS validation and antenna calibration into practice. A major factor which has contributed to the successful completion of this exercise was the fact that all measurements were traceable to national standards. This allowed direct comparison of all the measurement results by maintaining constant reference values.
{"title":"EMC antenna calibration sites (30 MHz to 1 GHz)-putting theory into practice","authors":"J. Hattingh","doi":"10.1109/COMSIG.1998.736965","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736965","url":null,"abstract":"The CE directives on EMC which came into effect on 1st January 1996, have led to an increasing awareness of the uncertainty of measurements in radiated emissions. EMC antenna calibration, and open area test site (OATS) validation, are two of the topics which now feature prominently in virtually any discussion on the subject of EMC. The South African Bureau of Standards constructed a new OATS in 1993, and the validation of this site was followed by a number of antenna intercomparison exercises. An application for accreditation by the National Laboratory Accreditation Service (NLA) was submitted early in 1998, and the assessment took place on 15 April 1998. This paper will deal primarily with the process which was followed to put the theoretical concepts behind OATS validation and antenna calibration into practice. A major factor which has contributed to the successful completion of this exercise was the fact that all measurements were traceable to national standards. This allowed direct comparison of all the measurement results by maintaining constant reference values.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127693361","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736964
H. Reader, J. Cloete
This paper presents one perspective on EMC activities in South Africa. A review of past work is given and an overview of known work in the country is attempted. Three suggested categories of relevant EMC activity are proposed.
{"title":"A perspective on EMC in South Africa","authors":"H. Reader, J. Cloete","doi":"10.1109/COMSIG.1998.736964","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736964","url":null,"abstract":"This paper presents one perspective on EMC activities in South Africa. A review of past work is given and an overview of known work in the country is attempted. Three suggested categories of relevant EMC activity are proposed.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130268612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736913
M. Sellars, J. Porter, S. Greaves, A. Hopper, W. Fitzgerald
High speed TDMA wireless networks (such as radio ATM networks), require high data rate efficiency and fast turnaround times. In dispersive multipath channels, an equalizer is needed to remove ISI from the signal. The equalizer may be trained more quickly if its taps are preloaded with initial values. This paper describes a power ratio approximation method which produces estimates for the initial tap values. Simulation results demonstrate that these estimates are sufficiently accurate to considerably reduce the equalizer settling time. The performance and complexity of the method is compared with existing methods for calculating the initial tap values, and shown to offer advantages for high speed systems.
{"title":"Fast start-up equalizer for radio ATM","authors":"M. Sellars, J. Porter, S. Greaves, A. Hopper, W. Fitzgerald","doi":"10.1109/COMSIG.1998.736913","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736913","url":null,"abstract":"High speed TDMA wireless networks (such as radio ATM networks), require high data rate efficiency and fast turnaround times. In dispersive multipath channels, an equalizer is needed to remove ISI from the signal. The equalizer may be trained more quickly if its taps are preloaded with initial values. This paper describes a power ratio approximation method which produces estimates for the initial tap values. Simulation results demonstrate that these estimates are sufficiently accurate to considerably reduce the equalizer settling time. The performance and complexity of the method is compared with existing methods for calculating the initial tap values, and shown to offer advantages for high speed systems.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"263 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120881765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736919
K. Butchart, R. Braun
LEO satellites present widely varying signal conditions. Fixed modulation schemes are designed for the worst operating conditions and cannot take advantage of the better signal to noise conditions present at high elevations. An adaptive modulation scheme, which uses different constellation patterns with trellis coded modulation and a Reed Solomon outer code is proposed in this paper. The system is tested under AWGN noise and Rician/Rayleigh fading conditions. The system is found to provide good performance in AWGN and moderate fading conditions.
{"title":"An adaptive modulation scheme for low Earth orbit satellites","authors":"K. Butchart, R. Braun","doi":"10.1109/COMSIG.1998.736919","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736919","url":null,"abstract":"LEO satellites present widely varying signal conditions. Fixed modulation schemes are designed for the worst operating conditions and cannot take advantage of the better signal to noise conditions present at high elevations. An adaptive modulation scheme, which uses different constellation patterns with trellis coded modulation and a Reed Solomon outer code is proposed in this paper. The system is tested under AWGN noise and Rician/Rayleigh fading conditions. The system is found to provide good performance in AWGN and moderate fading conditions.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"2016 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128057806","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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