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Optimizing the performance of an LC oscillator for maximum power delivery to a load 优化LC振荡器的性能，使其能够向负载提供最大功率
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401443
S. MacPherson
{"title":"Optimizing the performance of an LC oscillator for maximum power delivery to a load","authors":"S. MacPherson","doi":"10.1109/AFRCON.2007.4401443","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401443","url":null,"abstract":"Using a common Pierce LC oscillator circuit it is demonstrated that by using the technique referred to as a load- line match, commonly used in the design of class A power amplifiers, it is possible to extract the maximum available power from an RF transistor for delivery to a specified load impedance. This results in the transistor being used to its full capacity resulting in the oscillator efficiency approaching the theoretical limit of 50%.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"135 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123467364","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
Teaching protocol exchanges over cellular air interfaces 在蜂窝空中接口上的教学协议交换
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401606
O. J. Oyedapo, X. Lagrange, P. Martins, B. V. van Wyk
{"title":"Teaching protocol exchanges over cellular air interfaces","authors":"O. J. Oyedapo, X. Lagrange, P. Martins, B. V. van Wyk","doi":"10.1109/AFRCON.2007.4401606","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401606","url":null,"abstract":"The evolutionary path taken by cellular standards to the current and future standards is incomplete without fully understanding the older standards. The comprehension of the GSM standard, specifically the procedures for protocols exchange over the air interface will help students understand radio resource allocation procedures in GPRS and UMTS, and will ultimately assist future communication engineers to be able to design and solve problems related to these cellular standards. In this paper we describe the novel architecture of our teaching software, developed and programmed in Java. We present all the user interfaces and show how it can be used to assist in teaching, by presenting how the mobile station and the GSM/GPRS network exchange data frames over the air interface with their associated protocols. Finally the uniqueness of this teaching tool was proved from the stand point of our modular architecture.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121500870","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
A comparison of mesh termination schemes for 2D scattering analysis using the finite element method 二维散射有限元分析中网格终止方案的比较
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401504
A. Young, D. Davidson
{"title":"A comparison of mesh termination schemes for 2D scattering analysis using the finite element method","authors":"A. Young, D. Davidson","doi":"10.1109/AFRCON.2007.4401504","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401504","url":null,"abstract":"When the finite element method is used for scattering problems, the outer boundary of the mesh has to be terminated appropriately so that it seems transparent to any outgoing waves. Various solutions to this problem have been developed and here three such methods are discussed and compared. These are absorbing boundary conditions, finite element boundary integral hybrid method and infinite elements. A basic two-dimensional scattering problem is used to compare these methods.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127769162","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
Low-complexity constrained LMMSE estimator for the sparse OFDM channels 稀疏OFDM信道的低复杂度约束LMMSE估计
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401614
E. Golovins, N. Ventura
{"title":"Low-complexity constrained LMMSE estimator for the sparse OFDM channels","authors":"E. Golovins, N. Ventura","doi":"10.1109/AFRCON.2007.4401614","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401614","url":null,"abstract":"In this article the constrained linear minimum mean squared error (CLMMSE) algorithm is presented for the multipath channel response estimation in the OFDM systems using equispaced and equipowered pilot subcarriers. It relies on tracking of the channel correlation and signal-to-noise ratio and has a low computational complexity due to the transform-domain processing and no matrix inversions required. The proposed algorithm exhibits a substantial performance improvement for the sparse channels (9 dB in MSE and 1.4 dB in BER), whereas for channels with the dense impulse responses its accuracy is equivalent to the LMMSE scheme with the robust design parameters.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125780872","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
Electromagnetic bandgap structures for printed circuit board EMC 用于印刷电路板EMC的电磁带隙结构
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401595
R. Geschke, E. Laubscher
{"title":"Electromagnetic bandgap structures for printed circuit board EMC","authors":"R. Geschke, E. Laubscher","doi":"10.1109/AFRCON.2007.4401595","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401595","url":null,"abstract":"This paper investigates the suppression of parallel- plate modes on printed circuit boards via electromagnetic bandgap structures (EBG). We consider planar structures on ground or power planes. Two unit-cell geometries are used to create a 4 x 4 lattice on two simple test boards, where connector ports represent vias. This is compared to a reference test board without these structures. Measured results show that, even with a simple arrangement, it is possible to suppress parallel-plate modes very effectively.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131833316","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
Non-priority QoS guarantee for next generation routers 下一代路由器的非优先级QoS保证
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401564
O. Salami, H. A. Chan, M. Dlodlo
{"title":"Non-priority QoS guarantee for next generation routers","authors":"O. Salami, H. A. Chan, M. Dlodlo","doi":"10.1109/AFRCON.2007.4401564","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401564","url":null,"abstract":"Virtual Output Queuing (VOQ) is a proffered queuing strategy that solves the head of line blocking (HoL) issue in routers implementing input queuing (IQ). Also, VOQ can achieve 100% throughput with an effective scheduler. However, most schedulers for VOQ are deterministic algorithms, which either provide QoS guarantee or do not. Even though these algorithms have high performance, they schedule packets arbitrarily or with priority thereby starving some traffic. These algorithms may become inadequate in future networks where data rate continues to increase and traffic with different QoS requirements co-exist. This paper recommends a probabilistic QoS guarantee for routers using VOQ. Probabilistic QoS guarantees for network traffic ensure fairness and prevent traffic starvation. A probabilistic scheduling algorithm termed Iterative Probabilistic Scheduling (IPS) is proposed. IPS guarantees probabilistic QoS with a basic mathematical operation as its scheduling policy. From simulation, it achieves a high throughput performance and does not starve traffic. IPS was used at the first stage of the Multi-stage Queuing and Scheduling (MQAS) architecture. MQAS is a two-stage queuing architecture with VOQ at the input and Output Queuing (OQ) at the output of the router.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130778386","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
Investigating the security of electrical power systems SCADA 调查电力系统SCADA的安全性
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401531
E. Chikuni, M. Dondo
{"title":"Investigating the security of electrical power systems SCADA","authors":"E. Chikuni, M. Dondo","doi":"10.1109/AFRCON.2007.4401531","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401531","url":null,"abstract":"Supervisory control and data acquisition (SCADA) systems control and monitor the majority of the utility networks today. The increased number of attacks on computer systems and computer networks has resulted in an increased concern of security issues in inter-networked industrial automation systems. Internal and external saboteurs pose a big threat that could disrupt power delivery. To give us a better understanding of the nature of the vulnerabilities to supervisory control and data acquisition system (SCADA) systems and highlight the need to defend and protect the SCADA systems from ongoing cyber threats, we investigate the vulnerabilities and ways to protect them which are unique to SCADA systems. We achieve this by studying SCADA communication systems as well as taking a survey of common SCADA vendors; we focus our attention to SCADA on the electric power grid. We find that SCADA vendors do not implement adequate security measures in their products, and we recommend that a security policy be put in place to ensure the security of the vital public infrastructures.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132903170","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: 46
The transfer and commercialisation of technology from south africa to foreign markets in the financial services industry 技术从南非向金融服务业外国市场的转让和商业化
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.7166/20-2-760
Francois H. Lubbe, A. Brent
{"title":"The transfer and commercialisation of technology from south africa to foreign markets in the financial services industry","authors":"Francois H. Lubbe, A. Brent","doi":"10.7166/20-2-760","DOIUrl":"https://doi.org/10.7166/20-2-760","url":null,"abstract":"International technology transfer (ITT) processes are complex, risky, and fail often. When financial services organisations have the opportunity to transfer their business model and core technologies to a foreign market, comprehensive technology and market research are compulsory. Numerous applicable theories and models in technology transfer were reviewed to develop such a model. Interviews with key individuals and focus group sessions were used to rank factors that affect the success of ITT in the financial services industry; more specifically the direct short term insurance industry. These success factors were implemented in the developed market evaluation model where the user is required to enter evaluation values for each factor. The evaluation model then delivers a value that represent the market potential. This model can be used to evaluate between one and many potential markets. Two factors an organisation must always be aware of is the influence stakeholders have on the ITT process and what ITT strategy is employed.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"296 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133710551","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
Figure-eight fibre lasers with NALM loops consisting of highly nonlinear dispersion shifted fibres for dense wavelength division multiplexing 图8光纤激光器与NALM环路组成的高度非线性色散位移光纤密集波分复用
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401621
D. Schmieder, P. Swart, A. Booysen
{"title":"Figure-eight fibre lasers with NALM loops consisting of highly nonlinear dispersion shifted fibres for dense wavelength division multiplexing","authors":"D. Schmieder, P. Swart, A. Booysen","doi":"10.1109/AFRCON.2007.4401621","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401621","url":null,"abstract":"We describe 'Figure-of-Eight' fibre lasers with NALM (Nonlinear Amplifying Loop Mirror) loops of 100 m, 200 m 300 m highly nonlinear dispersion shifted fibre and 50 m photonic crystal fibre. Apart from the NALM loops the rest of the fibre lasers consisted of normal single-mode fibre (SMF28). The fibre lasers produced mode-locked and Q-switched pulses. By varying the length of the NALM loop we generated a variety of short and long stable high peak power and low peak power pulses in the range from 2 ns to 104 ns. The length of the pulses depends on the length of the NALM loop and the pump diode power. By changing the setting of the polarization controllers we can manipulate the amplitude of the pulses, produce high and low pulses, step pulses, double or multiple pulses. The period of the pulses is equal to the round trip time. We present pulse widths, pulse peak power and spectral measurements in dependence of the pump diode power, and discuss the shapes and spectra of the laser pulses with reference to the transmission curves.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"121 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131677414","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: 5
Adaptive inverse quadratics interpolation with applications to vector fitting and the hankel transform of spectral domain green’s functions 自适应逆二次插值及其在谱域格林函数的向量拟合和汉克尔变换中的应用
AFRICON 2007 Pub Date : 2007-12-12 DOI: 10.1109/AFRCON.2007.4401441
L. Knockaert, D. De Zutter
{"title":"Adaptive inverse quadratics interpolation with applications to vector fitting and the hankel transform of spectral domain green’s functions","authors":"L. Knockaert, D. De Zutter","doi":"10.1109/AFRCON.2007.4401441","DOIUrl":"https://doi.org/10.1109/AFRCON.2007.4401441","url":null,"abstract":"In this contribution we discuss the translation- invariant interpolation of univariate functions by means of inverse quadratics radial basis functions. For the implementation we use an adaptive interpolation process which is a variant of a recently introduced adaptive residual subsampling method. It is shown that the interpolation process with the inverse quadratics kernel also provides an excellent pre-processing interface when used in conjunction with the popular vector fitting algorithm. This results in a composite algorithm, performing the sampling and modelling of the given function in a fully automatic way. It also provides a platform for calculating the Hankel transform of spectral domain Green's functions.","PeriodicalId":112129,"journal":{"name":"AFRICON 2007","volume":"71 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133826119","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
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