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
  • 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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  • Calculation of LPC-based cepstrum coefficients using mel-scale frequency warping

    Publication Year: 1991, Page(s):17 - 21
    Cited by:  Papers (1)  |  Patents (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (248 KB)

    This paper describes a method for warping the frequency axis of cepstrum coefficients in a way analogous to the preprocessing performed by the human ear. The equations are derived and historical background relating to different warping scales is discussed. The calculation is a two-step procedure in which the bilinear transform is used to represent the LPC coefficients on a warped frequency scale. ... View full abstract»

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  • Preprocessing and tracking algorithms for automatic sperm analysis

    Publication Year: 1991, Page(s):64 - 68
    Cited by:  Papers (4)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (320 KB)

    The segmentation of images which consist of multiple objects (sperm cells) is discussed. The process must be fully automatic. Due to the poor quality of the images, it is of greater importance to detect than to recognize the objects, which must then be tracked with a multiple target tracking algorithm. Possible solutions are presented View full abstract»

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  • Wideband FM threshold extension techniques for satellite TV receivers

    Publication Year: 1991, Page(s):80 - 84
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (400 KB)

    The wideband FM threshold extension demodulators have been designed and constructed. A phase-locked loop demodulator at 840 MHz and a 600 MHz frequency-feedback demodulator were demonstrated to have better wideband FM threshold performance than a discriminator. The design procedure for the phase-locked demodulator could be used to realize an FM demodulator at the incoming C-band carrier frequency ... View full abstract»

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  • Modelling durations in hidden Markov models with application to word spotting

    Publication Year: 1991, Page(s):1 - 5
    Cited by:  Papers (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (292 KB)

    The conventional hidden Markov model models speech fairly well with the exception of parameters that are segment-based rather than frame-based. Duration of different acoustic segments, e.g. phonemes, falls into this category. Methods are described which solve this problem. For computational purposes sub-optimal methods are often used. This paper also deals with an improvement to such an algorithm ... View full abstract»

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  • 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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  • The fractal dimension of fricative speech sounds

    Publication Year: 1991, Page(s):12 - 16
    Cited by:  Papers (5)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (252 KB)

    The dimension of fricative speech sounds is determined using Hurst's rescaled range analysis. Fricatives are found to be fractal with constant dimension at least for the lag range of 300 μs to 3.5 ms. Unvoiced fricatives retain the same dimension for longer lags, with some examples remaining fractal up to a lag of 100 ms. Fractal dimension values ranging from 1.0 to 1.9 are obtained. Voiced fri... 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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  • A comparison between stationary and mobile digital VHF radio channels and channel models

    Publication Year: 1991, Page(s):74 - 79
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (332 KB)

    This paper presents results of a study undertaken to determine Fritchman (1967) channel models for mobile as well as stationary (linking two points geographically fixed with respect to each other) VHF radio channels. These models were investigated with respect to four modulation schemes FSK, DPSK, QPSK and 8-ary PSK. Predictions of P (m,n), the probability that a block o... 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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  • 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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  • 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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  • Edge-based dynamic thresholding of digital images

    Publication Year: 1991
    Cited by:  Papers (1)  |  Patents (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (60 KB)

    A dynamic grey-level thresholding scheme for the binary image segmentation is proposed. By the use of edge information and region-growing methods the effects of uneven illumination, noise and blurring are diminished, resulting in a better segmentation than is possible using global thresholding methods 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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  • 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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  • The application of the asymmetric polyphase filter in an SSB transceiver

    Publication Year: 1991, Page(s):85 - 92
    Cited by:  Papers (2)  |  Patents (13)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (420 KB)

    This paper describes the polyphase phase shift filter system of SSB generation and demodulation, and highlights the suitability of the polyphase filter for interfacing with CMOS analogue gates as a switching mixer. The performance is analyzed in the light of several years of production of a 1.6 to 30 MHz 100 W transceiver using this technique. Typically under conditions of power amplification the ... 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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  • 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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  • 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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  • Preprocessing of two-dimensional fingerprint images for fingerprint recognition

    Publication Year: 1991, Page(s):69 - 73
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (300 KB)

    Reliable fingerprint recognition requires extensive preprocessing to transform a greyscale image into a usable binary image from which features can be extracted for use in a classifier. This paper discusses two algorithms for preprocessing fingerprint images. Simulation results are presented 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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  • Algorithm to reduce glint induced radar tracking errors on a highly dynamic target

    Publication Year: 1991, Page(s):28 - 31
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (156 KB)

    An algorithm using a nonparametric rank detector is developed to detect and censor glint spikes on the angular error channels. The overall tracking improvement of a Kalman filter operating on this data was 15% on average 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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  • 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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