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COMSIG 1991 Proceedings: South African Symposium on Communications and Signal Processing

30-30 Aug. 1991

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  • COMSIG 1991 Proceedings. South African Symposium on Communications and Signal Processing (Cat. No.91TH0370-7)

    Publication Year: 1991
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    Freely Available from IEEE
  • Some new error-correcting (d,k) trellis codes for clock extraction on bandwidth limited channels

    Publication Year: 1991, Page(s):144 - 149
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (344 KB)

    Five new codes are suitable for use on channels where certain input constraints are imposed on the codestream. The construction techniques for these codes are presented. The codes were evaluated by determination of their bit error rates on the binary symmetric channel and measurement of their power spectral densities View full abstract»

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  • Complexity measures for cryptographic sequences

    Publication Year: 1991, Page(s):178 - 185
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (368 KB)

    Maximum order complexity, which is a generalization of linear complexity, is discussed. An efficient algorithm with linear time and memory requirements is available for its calculation. The Lempel-Ziv complexity measure forms the basis of a very efficient universal source coding algorithm. The relationship between these two complexity measures is discussed View full abstract»

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  • New multilevel line codes for baseband communication-an experimental study

    Publication Year: 1991, Page(s):138 - 143
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (240 KB)

    Codes considered for the North American ISDN and similar new multilevel line codes that comply with strict transmission channel input restrictions are discussed briefly. A short description of the experimental set up, used to evaluate the new multilevel line codes, is given. Measured eye patterns and spectra of some multilevel line codes are presented and compared with the line code 2B1Q, which wa... View full abstract»

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  • Recognition of syllable nuclei in continuous speech

    Publication Year: 1991, Page(s):105 - 109
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (244 KB)

    A new solution for the acoustic-to-articulatory inversion problem, based on distinctive region and mode theory, is suggested. Vowel sounds are coded in terms of the distinctive region synergy ratios which relate to the position of the body of the tongue in the front/back and high/low dimensions. This feature is used to study the phonetic role of coarticulation View full abstract»

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  • A secure protocol for public key exchange

    Publication Year: 1991, Page(s):172 - 177
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (320 KB)

    A new protocol provides a network with secure, authenticated key exchanges which thwart all known attacks. The time taken to exchange keys and the memory overhead are reduced partly due to the handshaking being two-way rather than three-way. Interaction with the key certification centre is limited to a minimum, a user only having to consult this public directory once. Problems of `reblocking' and ... View full abstract»

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  • Networking meteor-burst communications

    Publication Year: 1991, Page(s):132 - 137
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (244 KB)

    This paper describes the effect of network topologies and routing strategies in the meteor-burst communications environment. A range of network topologies is considered including trees, stars, and networks of various connectivities. Results indicate that delay time decreases exponentially with connectivity in meteor-burst networks View full abstract»

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  • HF channel sounding with polyphase CAZAC sequences

    Publication Year: 1991, Page(s):99 - 104
    Cited by:  Papers (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (288 KB)

    An alternative to the frequency modulated continuous wave (FMCW) or `chirp' channel sounder is presented. The suggested coded pulse sounder employs polyphase constant amplitude zero auto-correlation (CAZAC) sequences as opposed to the more commonly used maximal-length pseudo noise (PN) sequences. This paper presents techniques for extracting HF ionospheric layer height (or `range') and velocity da... View full abstract»

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  • A robust digital signal processing HF squelch

    Publication Year: 1991, Page(s):155 - 159
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (228 KB)

    A processing-efficient algorithm which detects the presence of speech in a low signal-to-noise (SNR) environment is proposed. A single delay auto-correlation function is used to detect the speech, and a circular buffer prevents loss of the first portion of the signal while the decision is made. Performance measurements are provided for different channel conditions and noise types View full abstract»

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  • Speech recognition using TES symbols

    Publication Year: 1991, Page(s):116 - 119
    Cited by:  Papers (1)  |  Patents (6)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (212 KB)

    This paper describes tests to determine whether time-encoded speech symbols can be used as a symbol feature set for speech recognition. For this purpose isolated word recognition (more specifically digit recognition) is investigated, using a vocabulary consisting of the 10 digits in Afrikaans. Three different speakers were used to compile the database. TES symbols were used to obtain classificatio... View full abstract»

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  • Design considerations and applications of a class of asymmetrically matched Nyquist low pass filters

    Publication Year: 1991, Page(s):166 - 171
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (312 KB)

    These filters have several advantages which make them particularly attractive for digital communications, e.g. low intersymbol interference and optimum post detection S/N ratios. Simulation results, design considerations and applications are presented. Comparisons between these filters and the conventional Square Root Nyquist LPF's are made View full abstract»

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  • Network management using 2 Mbit/s protection switching equipment

    Publication Year: 1991, Page(s):126 - 131
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (544 KB)

    The current telecommunication network is examined. The worldwide transition from a plesiochronous digital hierarchy (PDH) to a synchronous digital hierarchy (SDH) will provide an avenue for better management of the network as a whole. The structure of a Telecommunication Management Network (TMN) and the preconditions which it will place on telecommunication equipment are looked at. A locally desig... View full abstract»

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  • Inverse synthetic aperture radar images of moving targets

    Publication Year: 1991, Page(s):42 - 46
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (284 KB)

    The theory of using a low resolution, coherent radar to form images of non-cooperative targets is treated, and the most important problems related to implementation of the theory are identified. Compensation for target translational motion, aspect angle and angular velocity is discussed. An approach is developed for forming images taking into account the limitations of the motion compensation and ... View full abstract»

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  • Use of synthetic aperture and stepped-frequency continuous wave processing to obtain radar images

    Publication Year: 1991, Page(s):32 - 35
    Cited by:  Papers (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (152 KB)

    This paper outlines the use of synthetic aperture radar processing techniques to obtain images from a stepped-frequency continuous wave radar. Theoretical, simulation and experimental results are presented View full abstract»

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  • Edge adaptive image smoothing

    Publication Year: 1991, Page(s):58 - 62
    Cited by:  Patents (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (276 KB)

    A new edge-adaptive low-pass filter is proposed. This allows substantial removal of noise while maintaining clarity of edges and areas of high detail. Some results are presented and compared with those obtained by a standard low-pass filter View full abstract»

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  • Alignment of speech with a phonetic representation using continuous density hidden Markov models

    Publication Year: 1991, Page(s):22 - 27
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (316 KB)

    Sentence models are constructed from 7-state hidden Markov models utilising tied transitions within the Markov model and tied states within the sentence model. The HMMs generate output on state-to-state transition. The training is performed using unmarked sections of speech of which only the phonetic content is known. This paper also gives the formulae used for the training including the tied tran... View full abstract»

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  • On the sibilance problem in FM sound transmission

    Publication Year: 1991, Page(s):6 - 11
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (360 KB)

    The received sibilant sounds on FM transmission are often distorted because of portions of high amplitude values found in the Gaussian noiselike S's which over-modulate the instantaneous frequency beyond the IF filter band for a moment, and then RF receiver noise is demodulated. Pre-emphasis makes the effect worse. The broadcast peak program meters do not indicate peaks in random signals. Hard lim... View full abstract»

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  • Phase characteristics of the meteor burst channel

    Publication Year: 1991, Page(s):93 - 98
    Cited by:  Papers (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (292 KB)

    This paper presents a comparison between predicted and measured phase effects over a typical forward scatter meteor burst link. The theory and fundamentals of various phase effects are detailed. A phase measurement system is described briefly. Measured results confirm that phase aberrations due to early fast Doppler and body Doppler do not influence meteor burst channel capacity to any great exten... View full abstract»

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  • Recurrent nets and signal classification

    Publication Year: 1991, Page(s):150 - 154
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (288 KB)

    The feature space map used for analysis of feedforward backpropagation neural networks is extended to recurrent neural networks. The existence of difficulties in signal classification is shown. It is finally investigated whether this difficulty means that recurrent nets are not useful in signal-recognition tasks; the authors conclude that this is not so View full abstract»

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  • A family of binary group operations for block cipher applications

    Publication Year: 1991, Page(s):186 - 190
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (252 KB)

    A family of multiplication-like group operations over m-bit words is investigated. The operations are defined by a homomorphic mapping of binary words into the elements of a multiplicative group modulo 2kFn, where k is an integer ⩾1, and Fn is the n -th Fermat prime (n=0,1,2,3,4). The order of the multiplica... View full abstract»

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  • The automatic recognition of Afrikaans stop consonants in continuous speech by machine

    Publication Year: 1991, Page(s):110 - 115
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (396 KB)

    The stops are modelled at a subphoneme level using continuous hidden Markov models. Each state within a particular Markov model represents a specific segment that might occur within a stop, for example, silence. These models, as well as being able to identify an unknown stop, can provide a `fine transcription' used to obtain further features pertinent to stop recognition, such as voice onset time,... View full abstract»

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  • The lattice predictive decision-feedback equaliser in a multipath environment

    Publication Year: 1991, Page(s):160 - 165
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (328 KB)

    The predictive decision feedback equaliser (PDFE) has been suggested as a possible alternative to the so-called conventional DFE. In this paper the PDFE is compared with the double-channel version of the conventional DFE in a multipath environment. The structure is discussed and differences from the conventional DFE structure are highlighted. Computational complexities are also compared. A fractio... View full abstract»

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  • A real time, speaker independent, speech recognition system

    Publication Year: 1991, Page(s):120 - 125
    Cited by:  Papers (4)  |  Patents (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (304 KB)

    This paper describes the development of a system using continuous density hidden Markov models which incorporate probability density functions for time View full abstract»

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  • Processing of SIR-B SAR data of terrain near Cradock

    Publication Year: 1991, Page(s):47 - 52
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (304 KB)

    This paper presents an efficient method for the decoding of spaceborne synthetic-aperture radar data. Algorithms are proposed for converting a two-dimensional set of raw radar data into an image of the Earth's surface. Range correlation, azimuth correlation and range walk correction are considered. A software implementation of these algorithms is discussed View full abstract»

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  • A simulation of azimuth accuracy in pulsed surveillance radar

    Publication Year: 1991, Page(s):36 - 41
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (240 KB)

    The paper examines the performance of azimuth estimators applied in low pulse-repetition-frequency pulsed surveillance radars via Monte Carlo simulations, whose application enables the actual processing to be modelled accurately. Part 1 considers the aspect of simulation in radar processing and describes the technique of video signal simulation. Part 2 describes various processing techniques appli... View full abstract»

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