Pub Date : 1998-09-07DOI: 10.1109/COMSIG.1998.736942
P.J. Chitamu, F. Takawira
In this paper we study the performance of a simple and easy-to-implement open loop channel estimation and tracking strategy applicable to a DS-CDMA system. The scheme makes use of tentative channel estimates which are available whenever a CDMA signal is despread as part of the detection process for either multiuser decorrelator or MAI canceller based receivers. The algorithm employs a windowing approach to track and update the channel estimate. It takes advantage of the averaging effects of PN sequences in CDMA to improve channel estimates despite severe MAI or high co-channel interference levels. The estimated channel parameters are used to study the performance of a typical DS-CDMA receiver which uses a multistage interference cancellation scheme. The numerical results show that apart from the estimator being unbiased, it has a low mean estimation error. The performance degradation of a multi-user multistage interference cancellation scheme employing the channel estimator is shown to be small.
{"title":"Open loop channel estimation and tracking in DS-CDMA system with selective fading","authors":"P.J. Chitamu, F. Takawira","doi":"10.1109/COMSIG.1998.736942","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736942","url":null,"abstract":"In this paper we study the performance of a simple and easy-to-implement open loop channel estimation and tracking strategy applicable to a DS-CDMA system. The scheme makes use of tentative channel estimates which are available whenever a CDMA signal is despread as part of the detection process for either multiuser decorrelator or MAI canceller based receivers. The algorithm employs a windowing approach to track and update the channel estimate. It takes advantage of the averaging effects of PN sequences in CDMA to improve channel estimates despite severe MAI or high co-channel interference levels. The estimated channel parameters are used to study the performance of a typical DS-CDMA receiver which uses a multistage interference cancellation scheme. The numerical results show that apart from the estimator being unbiased, it has a low mean estimation error. The performance degradation of a multi-user multistage interference cancellation scheme employing the channel estimator is shown to be small.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"22 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":"122815240","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.1998.736987
I. Meier, J. B. de Swardt
A novel general linearization topology called 'error-feedback' is presented and applied to the linearization of amplifiers. Error-feedback uses the difference/error between (linearly) scaled input and output signal in its feedback loop to reduce nonlinearity. It does not rely on main-amplifier gain for linearization as does traditional feedback. Instead an auxiliary amplifier is introduced into the feedback loop, leaving the main amplifier's linear gain unaffected. Results from theory, and simulation as well as measured results complement each other. They show that linearization takes place over a continuous band. The topology shows prospects for concurrent multi-band linearization. Internal delay and phase shifts influence design limits and overall performance.
{"title":"Error-feedback for amplifier linearization","authors":"I. Meier, J. B. de Swardt","doi":"10.1109/COMSIG.1998.736987","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736987","url":null,"abstract":"A novel general linearization topology called 'error-feedback' is presented and applied to the linearization of amplifiers. Error-feedback uses the difference/error between (linearly) scaled input and output signal in its feedback loop to reduce nonlinearity. It does not rely on main-amplifier gain for linearization as does traditional feedback. Instead an auxiliary amplifier is introduced into the feedback loop, leaving the main amplifier's linear gain unaffected. Results from theory, and simulation as well as measured results complement each other. They show that linearization takes place over a continuous band. The topology shows prospects for concurrent multi-band linearization. Internal delay and phase shifts influence design limits and overall performance.","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":"129965831","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.1998.736928
J. Kotze
This paper describes the analysis, design and implementation of a new test target generation system for a height finding surveillance radar. The characteristics of the test target return have to match that of real returns to such a degree that the radar will respond to the simulated returns in a manner that is similar to its response to real returns.
{"title":"Design of a test target generation and calibration system for a height finding surveillance radar","authors":"J. Kotze","doi":"10.1109/COMSIG.1998.736928","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736928","url":null,"abstract":"This paper describes the analysis, design and implementation of a new test target generation system for a height finding surveillance radar. The characteristics of the test target return have to match that of real returns to such a degree that the radar will respond to the simulated returns in a manner that is similar to its response to real returns.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"15 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":"127647532","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.1998.736959
B. Worley, F. Takawira
This paper presents a soft handoff technique, which is based upon previous handoff schemes on adaptive traffic load shedding and a scheme on channel assignment strategies using soft handoff area sizing. We refer to the algorithm as adaptive load shedding with soft handoff sizing (ALS-SHS). It takes advantage of the soft handoff and soft capacity features of CDMA to dynamically adjust the soft handoff area of the base station so as to maintain a specified signal-to-interference ratio in the cell. This scheme is particularly useful in cases where hot-spot cells develop: these are heavily loaded cells surrounded by lightly loaded cells. Hot-spot cells occur in situations such as traffic accidents on a highway. The active mobiles in the cell may outnumber the capacity and an excessive increase in CDMA noise may, in the worst case, block all calls in the cell. Dynamic adjustment of the soft handoff area allows the reduction of traffic in the cell by altering the cell's soft handoff area so that users are accommodated based upon the SIR value within the cell.
{"title":"Handoff schemes in CDMA cellular systems","authors":"B. Worley, F. Takawira","doi":"10.1109/COMSIG.1998.736959","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736959","url":null,"abstract":"This paper presents a soft handoff technique, which is based upon previous handoff schemes on adaptive traffic load shedding and a scheme on channel assignment strategies using soft handoff area sizing. We refer to the algorithm as adaptive load shedding with soft handoff sizing (ALS-SHS). It takes advantage of the soft handoff and soft capacity features of CDMA to dynamically adjust the soft handoff area of the base station so as to maintain a specified signal-to-interference ratio in the cell. This scheme is particularly useful in cases where hot-spot cells develop: these are heavily loaded cells surrounded by lightly loaded cells. Hot-spot cells occur in situations such as traffic accidents on a highway. The active mobiles in the cell may outnumber the capacity and an excessive increase in CDMA noise may, in the worst case, block all calls in the cell. Dynamic adjustment of the soft handoff area allows the reduction of traffic in the cell by altering the cell's soft handoff area so that users are accommodated based upon the SIR value within the cell.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"8 9","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120873679","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.1998.736921
R. P. Narrainen, F. Takawira
CDMA networks are well-known for their time-varying interference-dependent capacity. However, many papers in the literature have used a single moment approach and assumed an average fixed value of CDMA capacity in mathematical analyses. We propose an analysis that takes into account the time-varying nature of CDMA capacity. We assume, from the central limit theorem, that the system interference is Gaussian and propose an expression for the system capacity. We present a traffic model for a power-controlled DS-CDMA network. Network performance is computed in terms of call blocking, probability of forced termination, grade of service, and erlang capacity.
{"title":"A traffic model for a power-controlled CDMA system","authors":"R. P. Narrainen, F. Takawira","doi":"10.1109/COMSIG.1998.736921","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736921","url":null,"abstract":"CDMA networks are well-known for their time-varying interference-dependent capacity. However, many papers in the literature have used a single moment approach and assumed an average fixed value of CDMA capacity in mathematical analyses. We propose an analysis that takes into account the time-varying nature of CDMA capacity. We assume, from the central limit theorem, that the system interference is Gaussian and propose an expression for the system capacity. We present a traffic model for a power-controlled DS-CDMA network. Network performance is computed in terms of call blocking, probability of forced termination, grade of service, and erlang capacity.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"15 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":"125350120","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.1998.736938
R.F. Uys
This paper presents an implementation of fractal image compression on a Texas Instruments TMS320C80 parallel processor chip. The work focuses on improving encoding speed. Speed gains are nearly linearly related to the number of processors used. An approach for reducing the number of calculations made, based on the variance of pixel values over sub-blocks of the image is presented. The various techniques employed allow a 512/spl times/512 pixel 256 grey-level image to be compressed in under 20 seconds, while maintaining peak signal to noise ratios of close to 30 dB. This paper also describes an extension of this work to allow colour images to be compressed.
{"title":"Parallel implementation of fractal image compression","authors":"R.F. Uys","doi":"10.1109/COMSIG.1998.736938","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736938","url":null,"abstract":"This paper presents an implementation of fractal image compression on a Texas Instruments TMS320C80 parallel processor chip. The work focuses on improving encoding speed. Speed gains are nearly linearly related to the number of processors used. An approach for reducing the number of calculations made, based on the variance of pixel values over sub-blocks of the image is presented. The various techniques employed allow a 512/spl times/512 pixel 256 grey-level image to be compressed in under 20 seconds, while maintaining peak signal to noise ratios of close to 30 dB. This paper also describes an extension of this work to allow colour images to be compressed.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"4 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":"131663447","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.1998.736927
L. Heystek, A. Broadhurst
It is well known that the beam width of a linear equally spaced array changes with the frequency of the signal being received. This affects the bearing accuracy with which a target can be located and the resolution between two targets. Also, the assessment of the frequency spectrum of the target signal is distorted unless the target is exactly aligned with the main response axis of the array's beam. Systems which have constant beam width within the frequency band of the receiver enable the bearing of a target to be determined to a fixed accuracy with a constant resolution. They overcome the deficiencies associated with conventional arrays. This paper presents a review of four different methods of achieving constant beam width. It is shown that the homothetic replica array has a simple analytic solution and shows potential for applications requiring bandwidths greater than one octave. This is demonstrated in the design and implementation of a twenty element hydrophone array with a constant beam width from 400 Hz to 3200 Hz. The experimental results are in agreement with those predicted by computer simulations. The main contribution of this paper is to show that the SHA technique proposed in 1970 by Smith, Hixon and Au is still the optimum choice in a practical sonar array system.
{"title":"A constant beam width towed sonar array","authors":"L. Heystek, A. Broadhurst","doi":"10.1109/COMSIG.1998.736927","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736927","url":null,"abstract":"It is well known that the beam width of a linear equally spaced array changes with the frequency of the signal being received. This affects the bearing accuracy with which a target can be located and the resolution between two targets. Also, the assessment of the frequency spectrum of the target signal is distorted unless the target is exactly aligned with the main response axis of the array's beam. Systems which have constant beam width within the frequency band of the receiver enable the bearing of a target to be determined to a fixed accuracy with a constant resolution. They overcome the deficiencies associated with conventional arrays. This paper presents a review of four different methods of achieving constant beam width. It is shown that the homothetic replica array has a simple analytic solution and shows potential for applications requiring bandwidths greater than one octave. This is demonstrated in the design and implementation of a twenty element hydrophone array with a constant beam width from 400 Hz to 3200 Hz. The experimental results are in agreement with those predicted by computer simulations. The main contribution of this paper is to show that the SHA technique proposed in 1970 by Smith, Hixon and Au is still the optimum choice in a practical sonar array system.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"165 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":"134490389","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.1998.736968
P. H. Pretorius, A. Britten, J. Van Coller, J. Reynders
Rogowski coils have been indicated to be ideal in many applications, including measurement of transient currents in substations. Research presently conducted by Eskom and the University of the Witwatersrand, focuses on the generation of unwanted common mode currents by disconnector operations. The use of Rogowski coils to study these currents forms an integral part of this work. Complementary coil design, application details and initial measurements, to support a better scientific understanding of the source of interference, are discussed in this paper.
{"title":"Experience in measuring disconnector-generated interference currents in a high voltage substation using Rogowski coils","authors":"P. H. Pretorius, A. Britten, J. Van Coller, J. Reynders","doi":"10.1109/COMSIG.1998.736968","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736968","url":null,"abstract":"Rogowski coils have been indicated to be ideal in many applications, including measurement of transient currents in substations. Research presently conducted by Eskom and the University of the Witwatersrand, focuses on the generation of unwanted common mode currents by disconnector operations. The use of Rogowski coils to study these currents forms an integral part of this work. Complementary coil design, application details and initial measurements, to support a better scientific understanding of the source of interference, are discussed in this paper.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"44 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":"133983980","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.1998.736923
Rudolph van der Merwe, J. du Preez
A new, general, mathematically sound technique is developed to integrate knowledge-based information with standard cepstral features into the formal HMM framework for phoneme recognition. By using these hybrid features, the maximum amount of information contained in the speech signal can be utilised. It is shown that a trivial extension of the statistical models used to model the cepstral features, cannot be used to model the hybrid feature vectors, as this results in a decrease in phoneme recognition accuracy. By using the proposed hybrid technique though, a statistically significant increase in phoneme recognition accuracy is achieved.
{"title":"Hybrid combination of knowledge- and cepstral-based features for phoneme recognition","authors":"Rudolph van der Merwe, J. du Preez","doi":"10.1109/COMSIG.1998.736923","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736923","url":null,"abstract":"A new, general, mathematically sound technique is developed to integrate knowledge-based information with standard cepstral features into the formal HMM framework for phoneme recognition. By using these hybrid features, the maximum amount of information contained in the speech signal can be utilised. It is shown that a trivial extension of the statistical models used to model the cepstral features, cannot be used to model the hybrid feature vectors, as this results in a decrease in phoneme recognition accuracy. By using the proposed hybrid technique though, a statistically significant increase in phoneme recognition accuracy is achieved.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"26 21","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113941532","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.1998.736963
J. Jonas
Radio astronomy is a non-commercial, passive user of the radio frequency spectrum. It is also the branch of fundamental scientific research that provides us with the most useful data on the origins of our universe. The recent and planned growth in radio communications systems presents a real threat to the future of radio astronomy as a viable scientific discipline. This paper attempts to put the problem of radio interference in perspective with regards to radio astronomy, and presents the case for the increased protection of the spectral bands allocated to radio astronomy.
{"title":"Threats to radio astronomy: now and the future","authors":"J. Jonas","doi":"10.1109/COMSIG.1998.736963","DOIUrl":"https://doi.org/10.1109/COMSIG.1998.736963","url":null,"abstract":"Radio astronomy is a non-commercial, passive user of the radio frequency spectrum. It is also the branch of fundamental scientific research that provides us with the most useful data on the origins of our universe. The recent and planned growth in radio communications systems presents a real threat to the future of radio astronomy as a viable scientific discipline. This paper attempts to put the problem of radio interference in perspective with regards to radio astronomy, and presents the case for the increased protection of the spectral bands allocated to radio astronomy.","PeriodicalId":294473,"journal":{"name":"Proceedings of the 1998 South African Symposium on Communications and Signal Processing-COMSIG '98 (Cat. No. 98EX214)","volume":"54 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":"124912408","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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