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

## Filter Results

Displaying Results 1 - 25 of 36
• ### COMSIG 1991 Proceedings. South African Symposium on Communications and Signal Processing (Cat. No.91TH0370-7)

Publication Year: 1991
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• ### Phase characteristics of the meteor burst channel

Publication Year: 1991, Page(s):93 - 98
Cited by:  Papers (2)
| | PDF (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»

• ### Preprocessing and tracking algorithms for automatic sperm analysis

Publication Year: 1991, Page(s):64 - 68
Cited by:  Papers (4)
| | PDF (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»

• ### Network management using 2 Mbit/s protection switching equipment

Publication Year: 1991, Page(s):126 - 131
| | PDF (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»

• ### A simulation of azimuth accuracy in pulsed surveillance radar

Publication Year: 1991, Page(s):36 - 41
| | PDF (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»

• ### Some new error-correcting (d,k) trellis codes for clock extraction on bandwidth limited channels

Publication Year: 1991, Page(s):144 - 149
| | PDF (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»

• ### The application of the asymmetric polyphase filter in an SSB transceiver

Publication Year: 1991, Page(s):85 - 92
Cited by:  Papers (2)  |  Patents (13)
| | PDF (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»

• ### A family of binary group operations for block cipher applications

Publication Year: 1991, Page(s):186 - 190
| | PDF (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»

• ### A real time, speaker independent, speech recognition system

Publication Year: 1991, Page(s):120 - 125
Cited by:  Papers (4)  |  Patents (2)
| | PDF (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»

• ### 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)
| | PDF (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»

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

Publication Year: 1991, Page(s):138 - 143
| | PDF (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»

• ### Wideband FM threshold extension techniques for satellite TV receivers

Publication Year: 1991, Page(s):80 - 84
| | PDF (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»

• ### Preprocessing of two-dimensional fingerprint images for fingerprint recognition

Publication Year: 1991, Page(s):69 - 73
| | PDF (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»

• ### Complexity measures for cryptographic sequences

Publication Year: 1991, Page(s):178 - 185
| | PDF (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»

• ### Speech recognition using TES symbols

Publication Year: 1991, Page(s):116 - 119
Cited by:  Papers (1)  |  Patents (6)
| | PDF (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»

• ### Edge adaptive image smoothing

Publication Year: 1991, Page(s):58 - 62
Cited by:  Patents (2)
| | PDF (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»

• ### 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)
| | PDF (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»

• ### Algorithm to reduce glint induced radar tracking errors on a highly dynamic target

Publication Year: 1991, Page(s):28 - 31
| | PDF (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»

• ### HF channel sounding with polyphase CAZAC sequences

Publication Year: 1991, Page(s):99 - 104
Cited by:  Papers (3)
| | PDF (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»

• ### Networking meteor-burst communications

Publication Year: 1991, Page(s):132 - 137
| | PDF (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»

• ### Inverse synthetic aperture radar images of moving targets

Publication Year: 1991, Page(s):42 - 46
Cited by:  Papers (1)
| | PDF (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»

• ### Recurrent nets and signal classification

Publication Year: 1991, Page(s):150 - 154
| | PDF (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»

• ### A comparison between stationary and mobile digital VHF radio channels and channel models

Publication Year: 1991, Page(s):74 - 79
Cited by:  Papers (1)
| | PDF (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»

• ### Edge-based dynamic thresholding of digital images

Publication Year: 1991
Cited by:  Papers (1)  |  Patents (3)
| | PDF (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»

• ### A secure protocol for public key exchange

Publication Year: 1991, Page(s):172 - 177
| | PDF (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»