By Topic

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

4-4 Oct. 1994

Filter Results

Displaying Results 1 - 25 of 37
  • 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
    Request permission for commercial reuse | PDF file iconPDF (32 KB)
    Freely Available from IEEE
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two hybrids for use in subscriber loops with delay

    Publication Year: 1994, Page(s):46 - 51
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (468 KB)

    Two new transformer-based hybrids aimed at improving performance and component count over existing hybrids are presented. These hybrids are for use in telephone subscriber loops where the problem of echo due to the combination of delay and impedance mismatch in the loop needs to be overcome View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Phase-plane analysis of phase-locked loops used for clock recovery

    Publication Year: 1994, Page(s):99 - 104
    Cited by:  Papers (1)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (388 KB)

    The transient analysis of phase-locked loops is not an easy analytical task. Although linearisation of these devices is common practice, the exact nature of the loop is not obtained. Using phase-plane techniques it is possible to determine both the transient and steady-state responses of phase-locked loops. We investigate the application of phase-plane techniques to a second-order phase-locked loo... View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fuzzy modeling and prediction of network traffic fluctuations

    Publication Year: 1994, Page(s):41 - 45
    Cited by:  Papers (2)  |  Patents (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (412 KB)

    Network management is a real-time observation and control action to optimize the grade of service of a network. More emphasis is being placed on the intelligent automatic exchange for stored program controlled (SPC) systems that are capable of real-time network management. The modeling of traffic characteristics and the prediction of future traffic flow are the first steps to efficient network con... View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A novel code phase synchronization network for direct sequence spread spectrum

    Publication Year: 1994, Page(s):95 - 98
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (356 KB)

    Direct sequence spread spectrum systems require that the receiver's replica of the spreading waveform be in code-phase and frequency lock with that of the transmitter's. Present methods of achieving synchronization involve correlation and energy detection. This paper presents the development of an alternative synchronization network. The network is a novel robust feedback loop where the input is t... View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Investigation of data transmission over SST channel

    Publication Year: 1994, Page(s):24 - 28
    Cited by:  Papers (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (348 KB)

    The paper concentrates on the effect of FEC on the supplementary signal transmission (SST) channel. The SST channel and its possible applications are discussed, as its uses are unexplored in South Africa. The noise properties of the channel are investigated, with and without forward error correction (FEC). A discussion of FEC is given to introduce the concept and functional operation of the system... View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 2-D radar imaging

    Publication Year: 1994, Page(s):146 - 151
    Cited by:  Papers (4)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (396 KB)

    Radar images generated with the 2-D Fourier transform of the scattered field data limited in frequency and/or angle have poor resolution. This has led to the introduction of the hybrid method and 2-D super resolution techniques for limited field data. However, the images contain no amplitude information of the various scattering centers. In this study, a modified hybrid method and 2-D AR technique... View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rock recognition using feature classification

    Publication Year: 1994, Page(s):152 - 157
    Cited by:  Papers (3)
    Request permission for commercial reuse | Click to expandAbstract | PDF file iconPDF (512 KB)

    A knowledge based approach to finding fixed size rocks within an image is described. It is intended to be a building block within a multiresolution system. Each point is hypothesised to be a rock and a region surrounding it is labelled using knowledge of rock characteristics. Twelve features are then measured and used to test the hypothesis by means of a combination of thresholding and k-nearest-n... View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 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»

    Full text access may be available. Click article title to sign in or learn about subscription options.