Doctoral Degrees (Electronic Engineering)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6867

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An adaptive protocol for use over meteor scatter channels.
(1987) Spann, Michael Dwight.; Broadhurst, Anthony D.
Modem technology has revived interest in the once popular area of meteor scatter communications. Meteor scatter systems offer reliable communications in the 500 to 2000 km range all day, every day. Recent advances in microprocessor technology have made meteor scatter communications a viable and cost effective method of providing modest data rate communications. A return to the basic fundamentals has revealed characteristics of meteor scatter propagation that can be used to optimize the protocols for a meteor scatter link. The duration of an underdense trail is bounded when its initial amplitude is known. The upper bound of the duration is determined by maximizing the classical underdense model. The lower bound is determined by considering the volume of sky utilized. The duration distribution between these bounds is computed and compared to measured values. The duration distribution is then used to specify a fixed data rate, frame adaptive protocol which more efficaciously utilizes underdense trails, in the half duplex environment, than a non-adaptive protocol. The performance of these protocols is verified by modeling.
Neural networks and early fast Doppler for prediction in meteor-burst communications systems.
(1994) Fraser, David Douglas.; Broadhurst, Anthony D.
In meteor-burst communications systems, the channel is bursty with a continuously fluctuating signal-to-noise ratio. Adaptive data rate systems attempt to use the channel more optimally by varying the bit rate. Current adaptive rate systems use a method of closed-loop decision-feedback to control the transmitted data rate. It is proposed that an open-loop adaptive data rate system without a decision feedback path may be possible using implicit channel information carried in the first few milliseconds of the link establishment probe signal. The system would have primary application in low-cost half-duplex telemetry systems. It is shown that the key elements in such a system would be channel predictors. The development of these predictors is the focus of this research. Two novel methods of predicting channel parameters are developed. The first utilises early fast Doppler information that precedes many long duration, large signal-to-noise-ratio overdense trails. The presence of early fast Doppler at the trail commencement is used as a toggle to operate at a higher data rate. Factors influencing the use of early fast Doppler for this purpose are also presented. The second method uses artificial neural networks. Data measured during trail formation is processed and presented to the neural networks for prediction of trail parameters. Several successful neural networks are presented which predict trail type, underdense or overdense, and peak trail amplitude from the first 50ms of the trail's lifetime. This method allows better estimation of the developing trail. This fact can be used to implement a multi-rate open-loop adaptive data rate system.
Optimized digital signal processing algorithms applied to radio communications.
(1992) Carter, Alan James Auchmuty.; Broadhurst, Anthony D.
The application of digital signal processing to radio communications has come of age with the advent of low power, high speed microprocessors and over the past five years, various transceiver architectures, utilizing this new technology have been extensively researched. Due to the flexible nature of a software based transceiver, a myriad of possible applications exist and currently the emphasis is on the development of suitable algorithms. The principal aim of this research is the derivation of optimized digital signal processing algorithms applicable to three separate areas of radio communications. Optimized, as used by the author within this dissertation, implies a reasonable compromise between performance, complexity and numerical processing efficiency. This compromise is necessary since the algorithms are applied to a portable transceiver where power consumption, size and weight are limited. The digital signal processing algorithms described by this research is as follows:- 1. The derivation and assessment of a multirate speech amplitude modulation demodulator which exhibits low distortion (typically less than 2%) for a wide range of modulation indices, carrier frequency offsets and deviations. The demodulator is processing efficient and requires only five multiplications and five decisions for every output sample. 2. The derivation and assessment of a low sampling rate speech frequency modulation demodulator for signals whose bandwidth exceed quarter the sampling frequency. The demodulator exhibits low distortion (typically less than 2%) and is processing efficient requiring eighteen multiplications and three decisions for every output sample. 3. The derivation and assessment of a multirate single-sideband suppressed carrier automatic frequency control system which is a combination of a simple second order adaptive line enhancer and a digital phase-locked loop. The processing efficient automatic frequency control system is suited for low signal to noise power conditions, in both stationary and mobile communication channels.
Predicted and measured arrival rates of meteors over forward-scatter links.
(1991) Mawrey, Robert Stanley.; Broadhurst, Anthony D.
Investigations into currently accepted methods of modelling variations in the arrival rate of meteors over forward-scatter meteor links have revealed some shortcomings. In these investigations, particular emphasis is placed on the work of Rudie due to its current acceptance in the literature. The non-uniform radiant distribution of meteors measured by Davies and modelled by Rudie, is critically examined and predictions using these models are compared with measured results taken over two forward-scatter links in the Southern Hemisphere. A new, alternative method of including the effect of non-uniform radiant distributions on the predicted arrival rate of meteors is given. The method used by Rudie to model Davies' measured radiant distribution is shown to be unnecessarily complicated and a simpler alternative is given. Furthermore, Rudie's distribution is shown not to be derived from a particular set of Davies' results as implied by Rudie. Other non-uniform distributions of meteors are also investigated. Comparisons between monthly-averaged daily cycles of measured and predicted arrival rates of meteors for a midpath and an endpath meteor link are used to reveal the validity and limitations of the published distributions. A new graphical method is used to aid in determining the validity and limitations of the non-uniform distributions. Discrepancies in the published predicted and measured annual variations in the arrival rate of meteors are investigated. Contrary to recently published information, predicted annual variations in the arrival rate of meteors for meteor radiants close to the ecliptic are shown to be comparable to measured results.
A proportional timing generator for measuring intermodulation product distortion on television transposers.
(1989) Bouwer, Paul Frederick.; Broadhurst, Anthony D.
Broadcasting authorities presently measure intermodulation distortion by applying a three tone simulation of a composite video and sound signal to the transposer and then measuring the relative amplitude of the major in-band intermodulation product (nominally at vision carrier frequency plus 1,57 MHz in the 625 line I/PAL System) on a spectrum analyser. This method is slow and requires a skilful operator to achieve repeatable results. Furthermore it tests the common RF amplification equipment at one luminance level and one chrominance level and therefore does not subject the transposer equipment to operation over its full range. A new sampling measurement technique has been proposed which overcomes all these problems by selectively mixing, while transmitting a colour bar test pattern, the demodulated output video signal of the frequency transposer with a pulse train coinciding with a particular colour. This thesis describes the design of a very stable proportional timing generator and its application to the measurement of intermodulation distortion on frequency transposers. The timing generator, which locks automatically onto the video signal and produces narrow sampling pulses which coincide accurately with a particular section of each line over a 50°C temperature range, is applicable to all PAL and NTSC TV Systems.

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Browsing Doctoral Degrees (Electronic Engineering) by Author "Broadhurst, Anthony D."