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A digital image watermarking scheme based on localised wavelet coefficients' dependency 一种基于局部小波系数相关性的数字图像水印方案
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308153
Ruth Dili Buse, E. Mwangi
{"title":"A digital image watermarking scheme based on localised wavelet coefficients' dependency","authors":"Ruth Dili Buse, E. Mwangi","doi":"10.1109/AFRCON.2009.5308153","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308153","url":null,"abstract":"A wavelet based robust image watermarking scheme in which a binary image is embedded in the horizontal and vertical quadrants of a wavelet transformed image is proposed. The algorithm exploits the intercoefficients relationship within a DWT block of a predetermined size. Only one wavelet coefficient is perturbed slightly in order to embed a single bit of the watermark and also to produce a watermarked image of high perceptual quality. The embedded DWT coefficients block is selected by the use of a secret key in order to enhance the security of the scheme. The retrieval process is blind and only requires the knowledge of the key. Results, obtained by MATLAB simulation have been used to confirm the feasibility and effectiveness of the proposed algorithm against common attacks such as lossy image compression, low pass filtering, additive white gaussian noise, and image cropping.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114292026","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}
引用次数: 2
Empirical analysis of the effect of parasitics and of reverse recovery as an amplitude error on distortion in a class D audio amplifier D类音频放大器中寄生和反向恢复作为幅度误差对失真影响的实证分析
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308132
F. Koeslag, H. Mouton, H. J. Beukes
{"title":"Empirical analysis of the effect of parasitics and of reverse recovery as an amplitude error on distortion in a class D audio amplifier","authors":"F. Koeslag, H. Mouton, H. J. Beukes","doi":"10.1109/AFRCON.2009.5308132","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308132","url":null,"abstract":"An analysis of the effect of parasitics and reverse recovery on harmonic distortion in a class D audio amplifier is performed in this paper. The error sources under investigation are modelled empirically as an amplitude error, after which an existing strategy based on Newton's numerical method is implemented to simulate its effect within the audible band. The results are compared to existing timing errors to determine its degree of dominance.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126809152","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}
引用次数: 1
A duopoly pricing model under congestion-sensitive end-users 对拥塞敏感的终端用户的双寡头定价模型
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308160
Hailing Zhu, A. Nel, W. Clarke
{"title":"A duopoly pricing model under congestion-sensitive end-users","authors":"Hailing Zhu, A. Nel, W. Clarke","doi":"10.1109/AFRCON.2009.5308160","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308160","url":null,"abstract":"In this paper we study a duopoly pricing model under congestion-sensitive end-users by investigating a two access point (AP) providers' price competition in a Wireless Mesh Network (WMN). The two AP providers resale IP-based service for possibly different prices and quality-of-service (QoS) to the end-users. The interactions among the two AP providers and their end-users are modeled using a two stage noncooperative game. In Stage 1, the AP providers set their prices to maximize their individual profits respectively. In Stage 2, given the price and QoS combinations offered by both AP providers, the endusers decide which AP to seek service from or opt out of both APs. Then the game returns to Stage 1, in which both AP providers adjust their optimal prices based on the decisions of the endusers to seek equilibrium among themselves and their end-users. With this game theoretical approach, we develop an analytical framework to identify the Nash equilibrium prices.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121811301","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}
引用次数: 2
Design and implementation of a topology control scheme for Wireless Mesh Networks 无线网状网络拓扑控制方案的设计与实现
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308242
P. Mudali, T. Nyandeni, N. Ntlatlapa, M. Adigun
{"title":"Design and implementation of a topology control scheme for Wireless Mesh Networks","authors":"P. Mudali, T. Nyandeni, N. Ntlatlapa, M. Adigun","doi":"10.1109/AFRCON.2009.5308242","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308242","url":null,"abstract":"The Wireless Mesh Network (WMN) backbone is usually comprised of stationary nodes but the transient nature of wireless links results in changing network topologies. Topology Control (TC) aims to preserve network connectivity in ad hoc and mesh networks and an abundance of theoretical results on the effectiveness of TC exist. Practical evaluations of TC schemes that provide gradual transceiver power adjustments for the WMN backbone are however in their infancy. In this paper we investigate the feasibility of power control in a popular WMN backbone device and design and evaluate an autonomous, light-weight TC scheme called PlainTC. An indoor test-bed evaluation shows that PlainTC is able to maintain network connectivity, achieve significant transceiver power savings and reduce MAC-level contention but that no significant reductions in physical layer interference were realised. The evaluation has also highlighted the danger of associating power savings with network lifetime. Further larger-scale experiments are required to confirm these results.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"377 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122815640","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}
引用次数: 18
Common mode noise in three-level DC-DC converters 三电平DC-DC变换器的共模噪声
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308155
I. Grobler, M. Gitau
{"title":"Common mode noise in three-level DC-DC converters","authors":"I. Grobler, M. Gitau","doi":"10.1109/AFRCON.2009.5308155","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308155","url":null,"abstract":"This paper demonstrates how conducted Electromagnetic Interference (EMI) can be easily analysed utilising an inexpensive and user friendly software package called Micro Cap 9 developed by Spectrum Software®. Other software packages generally used for accurate conducted EMI simulation purposes, such as SABER® is inaccessible to the general designer due to cost. The buck converter is shown as an example. Comparison is made between common mode currents in a standard two-level converter and also three-level derivations. Advantages of three-level converters include reduced switch voltage stress, lower distortion reactive power demand and improved dynamic response. The lower dv/dt should lead to lower electromagnetic noise generation. This paper will show that three-level buck DC-DC converters in general generate much lower common mode currents than conventional two-level buck converters. Further, reductions in common mode currents are achieved by using the improved three-level topologies that have been recently proposed.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123196649","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}
引用次数: 0
Multilevel harmonics current active compensator for DC feeding line 直流馈线多电平谐波电流有源补偿器
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308121
M. Fioretto, F. Liccardo, P. Marino, G. Raimondo, L. Rubino, G. Torre
{"title":"Multilevel harmonics current active compensator for DC feeding line","authors":"M. Fioretto, F. Liccardo, P. Marino, G. Raimondo, L. Rubino, G. Torre","doi":"10.1109/AFRCON.2009.5308121","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308121","url":null,"abstract":"In this paper a new DC line current compensator is presented. The proposed converter is able to compensate very low amplitude current harmonics and is very useful in railway applications where harmonic pollution can produce interference in the signaling systems over DC lines. The active compensator is modular and composed by multiple cells connected in series and controlled in order to minimize the modulation current ripple. Moreover a design criteria are shown and simulation results demonstrate the effectiveness of the proposed solution.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131320888","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}
引用次数: 2
Theory versus practical in a curriculum for engineering students — A case study 工程专业学生课程中的理论与实践——个案研究
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308419
J. Swart
{"title":"Theory versus practical in a curriculum for engineering students — A case study","authors":"J. Swart","doi":"10.1109/AFRCON.2009.5308419","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308419","url":null,"abstract":"fusing theory and practical in a curriculum for engineering students is a core academic function of a University of Technology. The department of Electronic Engineering at the Vaal University of Technology places particular emphasis on this fusion by means of interactive classroom sessions combined with methodical laboratory work. A previous paper, presented at AFRICON 2007, highlighted several key reasons as to why this fusion must transpire in a curriculum for engineering students. However, comments received from the delegates at that conference highlighted one notable deficiency in the results. The theory before practical approach was only applied to a single experiment on phase lock loops, while the practical before theory approach was solely used with a transmission line experiment. It was therefore suggested that these two approaches be reversed with regard to the relevant practical assignments. The theory before practical approach revealed a much higher average pass rate over the three year study period, proving it to be the preferred method for fusing theory and practical in a curriculum for engineering students. Nevertheless, this study did reveal that a mixed-method approach is still viable for senior engineering students.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126336208","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}
引用次数: 9
Dynamic control of an electrical wheelchair on an incline 电动轮椅在斜坡上的动态控制
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308254
S. O. Onyango, Y. Hamam, M. Dabo, Karim D Djouani, G. Qi
{"title":"Dynamic control of an electrical wheelchair on an incline","authors":"S. O. Onyango, Y. Hamam, M. Dabo, Karim D Djouani, G. Qi","doi":"10.1109/AFRCON.2009.5308254","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308254","url":null,"abstract":"Safe mobility of the disabled is one of the major reasons for the study of electric powered wheelchairs. To achieve absolute safety - where possible accident is not attributed to by the user's inability, the wheelchair should be as easy as possible to control in nearly every kind of environment. A reliable controller can only be designed from a reliable dynamic model. In this paper, consider a 3D dynamic model of a powered wheelchair having two active hind wheels and two front passive caster wheels has been considered. The developed model takes into account dynamic situations of the wheelchair in both uphill and downhill movements as well as movements on flat surfaces. Euler Lagrange procedure has been used in the derivation of the model's equation of motion then gravitational force added. Input-output feedback linearisation has then been applied in the development of the control law used in the model.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"79 22","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131770072","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}
引用次数: 8
The solid-state transformer concept: A new era in power distribution 固态变压器概念:配电的新时代
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308264
J. van der Merwe, H. Mouton
{"title":"The solid-state transformer concept: A new era in power distribution","authors":"J. van der Merwe, H. Mouton","doi":"10.1109/AFRCON.2009.5308264","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308264","url":null,"abstract":"This paper considers the solid-state transformer concept as a viable alternative to the line frequency transformer in distribution circuits. The benefits of the concept are presented in terms of improvements to problem areas currently experienced on distribution networks as well as envisaged future or fringe benefits. Some barriers to universal acceptance of the concept are also identified, with the effects of these barriers analysed and discussed below.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128208836","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}
引用次数: 73
A comparison of controllers for improving the time response of NiTi wires 改善镍钛导线时间响应的控制器比较
AFRICON 2009 Pub Date : 2009-11-03 DOI: 10.1109/AFRCON.2009.5308412
R. Velázquez, E. Pissaloux
{"title":"A comparison of controllers for improving the time response of NiTi wires","authors":"R. Velázquez, E. Pissaloux","doi":"10.1109/AFRCON.2009.5308412","DOIUrl":"https://doi.org/10.1109/AFRCON.2009.5308412","url":null,"abstract":"This paper presents a comparative theoretical study of the performance of a set of controllers for improving the speed of actuators based on shape memory alloys (SMAs), especially on Nitinol (NiTi). To prevent overheating and thermal fatigue, these controllers take into account the maximum heating current at which a NiTi element can safely be heated. The thermal behavior of NiTi is first modeled for calculating the time response and, based on the suggested model, we show that hysteresis due to phase transformation can be neglected for rapid heating, thus simplifying the model to a linear problem. We present then the design and performance of a set of linear controllers. Simulation results show a substantial increase in actuation speed.","PeriodicalId":122830,"journal":{"name":"AFRICON 2009","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124645450","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}
引用次数: 3
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