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Communications and Signal Processing, 1994. COMSIG-94., Proceedings of the 1994 IEEE South African Symposium on

Date 4-4 Oct. 1994

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  • Proceedings of COMSIG '94 - 1994 South African Symposium on Communications and Signal Processing

    Publication Year: 1994
    Request permission for commercial reuse | PDF file iconPDF (168 KB)
    Freely Available from IEEE
  • Author index

    Publication Year: 1994
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    Freely Available from IEEE
  • An implementation of an elliptic curve cryptosystem

    Publication Year: 1994, Page(s):85 - 90
    Cited by:  Papers (1)  |  Patents (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (396 KB)

    We discuss the implementation of the analog of the ElGamal (1984) public-key cryptosystem using elliptic curves over finite fields. More specifically, the kind of elliptic curve used is a supersingular curve over GF(2208). Furthermore, it is shown that this cryptosystem is cryptographically secure to the best of current knowledge View full abstract»

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  • Security of Levenshtein synchronization error correcting codes

    Publication Year: 1994, Page(s):81 - 84
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (252 KB)

    A new cryptographic system using single insertion/deletion (synchronization) error correcting codes is described. The new system's security is evaluated according to three basic attacks. Supplementary practical results are used to demonstrate that the new system is computationally secure View full abstract»

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  • Some non-linear effects of quantization in phase-locked loops

    Publication Year: 1994, Page(s):116 - 120
    Cited by:  Papers (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (352 KB)

    The combination of feedback and quantization causes special problems. (Each on its own has its problems, like instability and round-off errors.) The main problem is the likely existence of multiple equilibria of limit cycles. Another is possible coherence between the input signal and quantization error or limit cycle, making the error indistinguishable from whatever signal characteristic we want t... View full abstract»

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  • Speaker recognition over HF radio after automatic speaker segmentation

    Publication Year: 1994, Page(s):171 - 176
    Cited by:  Papers (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (584 KB)

    The author presents a new method to segment speakers in HF radio conversations. An experiment is conducted to evaluate how this segmentation method affects automatic speaker identification. It is found that, for the database, the segmentation method does not degrade identification performance relative to manual speaker segmentation and also that the automatic speaker identification is promising wh... View full abstract»

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  • VLSI appropriate design of a trace-back Viterbi decoder

    Publication Year: 1994, Page(s):76 - 80
    Cited by:  Papers (1)  |  Patents (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (376 KB)

    This paper concerns the research into the implementation of an efficient Viterbi algorithm for the decoding of convolutional codes. The original algorithm, as presented by Truong (see IEEE Trans. Commun. Technol., vol.40, no.3, p.616-624, 1992), is described, with many new points being noted. A detailed discussion of the improvements made to the algorithm is included, along with a full example of ... View full abstract»

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  • Using correlation filters to classify aircraft down-range radar profiles

    Publication Year: 1994, Page(s):132 - 137
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (404 KB)

    This paper details a classifier which uses correlation filters to discriminate between down-range profiles of radar targets. Down-range profiles are formed via an inverse FFT from frequency data obtained with the MTI (Moving Target Identification) process from successive scans of the aircraft. MTI separates the reflected backscatter of a moving target from the backscatter of the stationary environ... View full abstract»

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  • Improved linear prediction through optimal signal discretization

    Publication Year: 1994, Page(s):108 - 115
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (244 KB)

    We consider the problem of predicting a target signal {y},as a linear combination of a set of explanatory signals {xi}. In order to reduce the prediction error, we determine an optimal number of thresholds and their values for each signal {xi} by maximising the correlation between the thresholded explanatory signals and the target signal {y}. We extend this pairwise quantizat... View full abstract»

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  • Formant tracking using the wavelet-based DST

    Publication Year: 1994, Page(s):183 - 189
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (400 KB)

    Speech signals vary rapidly with time. To track these changes in time, one requires a transform which maps time-magnitude signals into a time-frequency space representing the original signal. The Fourier transform (FT) is the standard time-to-frequency transform. The sine and cosine sinusoidal waves used by the FT have infinite support in t, and windowing is required to obtain any meaningful spati... View full abstract»

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  • On the TV ghost image model

    Publication Year: 1994, Page(s):168 - 170
    Cited by:  Patents (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (228 KB)

    Multipath interference causes a TV ghost image that is either an attenuated, shifted version of the original image, or an attenuated, shifted Hilbert transform of the original, or a bit of both. This complete model for the ghost image will be proven by modeling the vestigal sideband TV signal as a single sideband signal, after which the multi-path signal will be demodulated View full abstract»

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  • A comparison of three families of spreading sequences for CDMA applications

    Publication Year: 1994, Page(s):68 - 75
    Cited by:  Papers (6)  |  Patents (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (592 KB)

    A comparison between three different families of spreading sequences for an all-digital Direct sequence spread spectrum code division multiple access (DSSS CDMA) modem is presented. The families considered are binary Gold and Kasami and polyphase generalised chirp-like (GCL) sequences. Comparisons are made with regard to the autocorrelation, cross-correlation, family size, length and ease of imple... View full abstract»

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  • Echo phenomena in telephone systems employing speech compression

    Publication Year: 1994, Page(s):29 - 32
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (304 KB)

    Echoes on subscriber voice circuits have only been a problem when international satellite links are involved. This is due to a reflection at the far end combined with a round trip delay of approximately 500 ms. To provide an acceptable service, the local PTT will provide echo cancelling facilities on these international routes. These facilities are not required for domestic routes since the worst ... View full abstract»

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  • Motion compensation for airborne SAR

    Publication Year: 1994, Page(s):128 - 131
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (276 KB)

    This paper reports on a motion compensation algorithm applicable for airborne SAR. The algorithm is described at an geometrical level to aid intuitive understanding and the equations used are given for easy implementation. The algorithm has been applied in the processing of ESAR data and found noticeably to improve image resolution View full abstract»

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  • New cepstrum algorithms

    Publication Year: 1994, Page(s):105 - 107
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (168 KB)

    New algorithms are introduced for computing 2N-1 points of the complex cepstrum and N unique points of the real cepstrum while using only N-point FFT calculations. These methods are compared to existing methods, and some indication is given of their applicability View full abstract»

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  • On the reduction of fractal image compression encoding time

    Publication Year: 1994, Page(s):158 - 161
    Cited by:  Papers (4)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (304 KB)

    Lossy image coding by partitioned iterated function systems, popularly known as fractal image compression, has recently become an active area of research. An image is coded as a set of contractive transformations in a complete metric space. As a result of a well known theorem in metric space theory, the set of contractive transformations (subject to a few constraints) is guaranteed to produce an a... View full abstract»

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  • A universal homophonic coding algorithm based on arithmetic coding

    Publication Year: 1994, Page(s):52 - 59
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (608 KB)

    We present a practical algorithm for the homophonic coding of a message source, as required for cryptographic purposes. The purpose of homophonic coding is to transform the output of a non-uniformly distributed message source into a random, uniformly distributed source sequence. This is achieved by mapping each source symbol into one of a set of homophones in a random way. The selected homophones ... View full abstract»

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  • A multi-oscillator approach to CPFSK signal creation

    Publication Year: 1994, Page(s):20 - 23
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (284 KB)

    The development of a MSK modulator/demodulator by Massey (1980) and the Hodgart and Schoones (see ibid p.211-216, 1992) implementation has prompted the development of a multi-oscillator multi-h modulator/demodulator. The approach taken has been an investigation and extension of basic CPFSK multi-oscillator modulator/demodulator design using digital logic. In this paper the multi-oscillator MSK mod... View full abstract»

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  • A new general runlength constraint for binary ARLL sequences

    Publication Year: 1994, Page(s):91 - 94
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (308 KB)

    We introduce a new general runlength constraint for binary asymmetrical runlength limited (ARLL) sequences. This constraint can be used on any channel requiring specific runlength constraints. It is shown that this new constraint generalises many previous runlength constraints which are widely used. We present some information theoretical aspects of the new constraint. Certain choices of runlength... View full abstract»

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  • Interconnection strengths and injected currents of a Hopfield neural net applied to an adaptive linear combiner

    Publication Year: 1994, Page(s):121 - 124
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (216 KB)

    Mathematical expressions for the interconnection strengths and injected currents of a Hopfield type neural network are derived for the case where the network is expected to perform as an adaptive algorithm of an adaptive linear combiner (adaline). It is shown that the performance of the neural network is theoretically optimum. The problem is basically a quadratic programming one, and it is shown t... View full abstract»

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  • Adaptive estimation of speech parameters

    Publication Year: 1994, Page(s):177 - 182
    Cited by:  Papers (1)  |  Patents (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (608 KB)

    Linear predictive coding (LPC), and transformations of it, is currently the most popular way of analysing speech signals. Major limitations of using a frame-based technique are that each frame is analysed in isolation of the rest while assuming the excitation source to be a white noise process. In order to reduce computation time, an all pole model is usually employed. In the present project an ad... View full abstract»

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  • Classification of aerospace targets using superresolution ISAR images

    Publication Year: 1994, Page(s):138 - 145
    Cited by:  Papers (4)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (488 KB)

    This paper describes investigations into a recognition system that takes the 2-D ISAR (inverse synthetic aperture radar) image of an aerospace target as input and classifies the target based on features calculated from the image. Four types of features were implemented, namely geometrical moments, invariant features based on moments, shape features, and quantized energy strips. Nearest-neighbour a... View full abstract»

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  • A discrete pseudo Wigner distribution spread spectrum detection procedure employing complex spreading sequences

    Publication Year: 1994, Page(s):33 - 40
    Cited by:  Papers (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (688 KB)

    An efficient quadratic time-frequency (TF) discrete pseudo Wigner distribution (DPWD) based detection procedure is proposed for utilisation in direct sequence spread spectrum (DSSS) receivers. A class of complex generalised chirp-like (GCL) perfect-squares minimum-phase constant-amplitude-zero-autocorrelation (PS-MP CAZAC) signature or spreading sequences is employed to facilitate communications i... View full abstract»

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  • Modelling and restoring images distorted by atmospheric turbulence

    Publication Year: 1994, Page(s):162 - 167
    Cited by:  Patents (2)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (784 KB)

    This paper investigates the mathematical description and modelling of atmospheric turbulence, as well as the restoration of images degraded by it. The effects on images are simulated on a computer as well as physically in the laboratory for a wide range of objects. These images are then also restored, with results presented throughout View full abstract»

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  • Deception in authentication channels with multiple usage

    Publication Year: 1994, Page(s):60 - 67
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (288 KB)

    By considering a simple but very general authentication code, we obtain some lower bounds on the probability of successful deception, through impersonation or substitution, if an authentication channel is used without a change of key after each message. In particular an authentication scheme proposed by Johanssen (see Designs, Codes and Cryptography, vol.4, p.69-81, 1994) is analysed, and found to... View full abstract»

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