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COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings最新文献

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The performance of an adaptive least squares lattice decision-feedback equalizer on a fading multipath HF channel 自适应最小二乘格决策反馈均衡器在衰落多径高频信道上的性能
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49308
L. Linde
{"title":"The performance of an adaptive least squares lattice decision-feedback equalizer on a fading multipath HF channel","authors":"L. Linde","doi":"10.1109/COMSIG.1988.49308","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49308","url":null,"abstract":"The performance of an adaptive lattice decision-feedback equalizer, originally proposed by F. Ling and J.G. Proakis (IEEE Trans. on Comm., vol.COM-33, no.4, p.348-56, 1985) is compared with that of transversal equalizer that uses a gradient tap adaptation algorithm operating in a periodic-channel estimation-mode. Results obtained over a simulated two-path HF channel model with a 1-ms differential multipath delay and 0.5-Hz fading rate show an approximately 5-dB advantage for the lattice equalizer for low signal-to-noise ratios (SNR), but only marginal improvement for high SNR. This phenomenon is primarily attributed to the occurrence of a significant number of flat fades during typical test runs over the two-path channel model, which accounts for the total lack of any form of diversity during these periods. Since diversity enhances modem performance in the presence of flat fades, the error rate plateau was significantly reduced by exploiting dual-polarization diversity without reducing the nominal bit speed of 2400 b/s.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126562051","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: 6
Optical fibre wavelength division multiplexing 光纤波分复用
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49311
S. Gunn
{"title":"Optical fibre wavelength division multiplexing","authors":"S. Gunn","doi":"10.1109/COMSIG.1988.49311","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49311","url":null,"abstract":"An overview is given of wave-length division multiplexing (WDM) as a means of expanding communication capacity and implementing special data techniques in a fiber-optic system. This technology is implemented by adding optical sources of different wavelengths at optical transmitting locations, then mixing (multiplexing) the optical signals and coupling them into an optical fiber where they travel to another location. The optical wavelengths are then separated (demultiplexed) and detected by optical receivers. Fundamentally, a wide band of wavelengths between 0.7 and 1.6 mu m exists for WDM applications. Even wider bandwidths will be available with the foreseeable development of infrared fibers. Topics covered include current and future applications of WDM, the current availability of WDM semiconductor laser/transmitters, optical-fiber taps and couplers, wavelength multiplexing/demultiplexing methods, and the use of WDM in local area networks.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131088618","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
Photo videotex-a proposal for picture communication in South Africa 图片视频文本——南非图片交流方案
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49300
J. Grove
{"title":"Photo videotex-a proposal for picture communication in South Africa","authors":"J. Grove","doi":"10.1109/COMSIG.1988.49300","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49300","url":null,"abstract":"An overview of the development of videotex is given, starting from the first Prestel system to the latest developments in videotex, namely photo videotex with CAPTAIN (character and pattern telephone access information network, developed by NTT in Japan) and picture Prestel (developed by British Telecom) as examples. It is noted that three upwards compatible videotex standards are supported by Beltel (the South African videotex system). It is proposed that image coding be used to provide an inexpensive and fast response photo videotex service in South Africa, compatible with Beltel. The different image coding solutions are discussed and reference is made to their advantages and disadvantages. The role that the integrated services digital network (ISDN) will play in this development is also outlined. The applications made available by this service are highlighted.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126128213","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
Linear mean square estimation of a Rayleigh variable corrupted with noise 被噪声破坏的瑞利变量的线性均方估计
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49307
J. Barnard, C. Pauw
{"title":"Linear mean square estimation of a Rayleigh variable corrupted with noise","authors":"J. Barnard, C. Pauw","doi":"10.1109/COMSIG.1988.49307","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49307","url":null,"abstract":"A linear mean-squared (LMS) estimation technique is proposed for the estimation of the true amplitude of a carrier in a Rayleigh fading channel in terms of the envelope of the noise-corrupted signal available at the receiver. The proposed method takes a finite number of equal-time spaced samples from the envelope of the noise-corrupted signal and then applies the Yule-Walker equations. A prerequisite in applying these equations is the a priori knowledge of two specific correlation functions: the autocorrelation function of the envelope of the noise-corrupted signal, and the cross-correlation function of the envelope of the noise-corrupted signal as well as the true amplitude of the signal. First the autocorrelation function of a stochastic signal with a Rayleigh probability density function is determined in terms of the autocorrelation function of its two orthogonal components. This expression is then used to determine the autocorrelation function of the envelope of the noise-corrupted signal. An expression is then derived for the required cross-correlation function. The results are implemented using the Yule-Walker equations and a sample quantity of ten.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126453736","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
Low bit rate video coding: an overview 低比特率视频编码:概述
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49302
M. Venter
{"title":"Low bit rate video coding: an overview","authors":"M. Venter","doi":"10.1109/COMSIG.1988.49302","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49302","url":null,"abstract":"An overview is given of low bit rate (m*64 kb/s, m=1.6) video coding using a generalized video codec. This codec uses a hybrid coding algorithm combining differential pulse-code modulation (DPCM) in the temporal domain and transform coding or vector quantization (VQ) in the spatial domain to code sequences of spatially and temporally subsampled images. The coder uses motion detection and estimation for more efficient prediction; the resulting motion vectors are also used in the decoder for motion-compensated interpolation of the images left out in the subsampling process. All the elements of the codec are discussed and some of the options available for each element are noted.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123977384","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
Parallel distributed processing: practical applications of neural networks in signal processing 并行分布式处理:神经网络在信号处理中的实际应用
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49306
J. A. Schoonees
{"title":"Parallel distributed processing: practical applications of neural networks in signal processing","authors":"J. A. Schoonees","doi":"10.1109/COMSIG.1988.49306","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49306","url":null,"abstract":"An introduction to artificial neural network models is presented, along with an overview of their practical application and potential applications in signal processing. Successful neural network implementations are described and their performances are compared to those of more traditional signal processing implementations. The Hopfield net, self-organizing feature maps, and the multilayer perceptron are reviewed. Implementation of neural nets in speech synthesis, speech recognition, target identification, image processing, pattern matching, error-correction coding, and neurocomputing are reported. Several ICs in production are briefly mentioned.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114213648","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: 4
The establishment of a radio refractivity data base for Southern Africa 为南部非洲建立一个无线电折射性数据库
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49318
J.W. Nel, S. Erasmus, S. Mare
{"title":"The establishment of a radio refractivity data base for Southern Africa","authors":"J.W. Nel, S. Erasmus, S. Mare","doi":"10.1109/COMSIG.1988.49318","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49318","url":null,"abstract":"The authors discuss the use of radiosonde data to produce a radio refractivity database for Southern Africa. The data consist of values for nine stations situated over Southern Africa; data for six years were analyzed. Lag corrections have not been applied on the data because of differing radiosonde design; geopotential heights are used instead of height calculated from the ascent rate. It is noted that the calculation of Delta N, the gradient of the atmospheric refractive index from ground level to an altitude of 1 km, and the Earth radius factor k should be found at 200 m and not on 1 km, since radiosystems operate in the first 200 m above ground level. Following CCIR norms, values of refractivity were calculated at surface level and at 1 km above surface and the Delta N derived from these values. The extent to which this method is a misleading approximation of reality is noted.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123158674","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: 12
Secure communication procedure for ISDN ISDN的安全通信程序
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49322
G. Claassen, G. Kuhn
{"title":"Secure communication procedure for ISDN","authors":"G. Claassen, G. Kuhn","doi":"10.1109/COMSIG.1988.49322","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49322","url":null,"abstract":"An overview of the basic concepts of encryption is given and a key distribution problem is analyzed that arises when encryption is implemented as the basis of security services in communication networks. A secure communications procedure based on a hybrid encryption system and an adaptive version of the proposed strong three-way authentication method of the CCITT and ISO is described for solving the problem of distributing encryption and decryption keys. The most important advantage of this procedure is that the user need only to approach a trusted third party once, when joining the network. In the hybrid system, a public-key algorithm is used to distribute secrete keys over the network which are then used as the keys for a conventional system to encrypt the data messages. The integration of the secure communication procedure in ISDN to perform key distribution in association with a circuit-switched connection is also described.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125645392","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
Computer aided design and analysis of SAW filters SAW滤波器的计算机辅助设计与分析
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1988-06-24 DOI: 10.1109/COMSIG.1988.49305
H. P. M. Hugo
{"title":"Computer aided design and analysis of SAW filters","authors":"H. P. M. Hugo","doi":"10.1109/COMSIG.1988.49305","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49305","url":null,"abstract":"The basic principles of surface acoustic wave (SAW) devices are discussed with specific reference to SAW filters. It is shown how digital filter theory can be applied to the design of SAW filters and a program based on this principle is presented. The effect of diffraction on surface acoustic wave bandpass filters is discussed and a program for the analysis of SAW filter responses including such diffraction is presented. Sample results are given, illustrating the severity of the effect of diffraction in SAW filters.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1988-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121572925","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
Approaches to speaker independent isolated word recognition 独立于说话人的孤立词识别方法
COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings Pub Date : 1900-01-01 DOI: 10.1109/COMSIG.1988.49299
J. du Preez
{"title":"Approaches to speaker independent isolated word recognition","authors":"J. du Preez","doi":"10.1109/COMSIG.1988.49299","DOIUrl":"https://doi.org/10.1109/COMSIG.1988.49299","url":null,"abstract":"The pattern recognition issues involved in speaker-independent isolated word recognition are considered. The discussion centers on results of experiments to assess four different techniques based on the hidden Markov model. These techniques are applied to the recognition of Afrikaan speech as uttered by seven male and three female speakers. The procedures for both classification of unknown speech and derivation of reference models are automated. Accuracy comparable with that of other researchers is obtained. Among the techniques discussed, those that utilize the continuous hidden Markov model give marked by better accuracy.<<ETX>>","PeriodicalId":339020,"journal":{"name":"COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114356961","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
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