Avionics System Maintenance Procedures are discussed in this thesis in the context of a BPhil project involving formal training in research methods and includes information obtained by investigating issues pertinent to aircraft avionics systems maintenance. Personnel matters, problem specification and identification, maintenance procedures, health and safety issues, and quality control issues are discussed in terms of their influence in effectively carrying out required maintenance. The work described in the thesis demonstrates that several research methods are applicable to, and effective for, gathering information on avionics systems maintenance. Evidence is presented to support the view that research of maintenance procedures can produce considerable benefits in terms of improved overall maintenance performance. A critical comparison of maintenance procedures used by British Aerospace and the Indonesian Air Force is included, and conclusions are drawn which highlight a number of significant possibilities for developing improved procedures. Specific recommendations for improving maintenance productivity are given, and the benefits of addressing issues of Continuing Professional Development, Health and Safety matters, problem identification, use of computer databases, particularly for information governed by Standards, are discussed.

The aims of the project were to investigate DC Thyristor Circuit Breaker (TCB) current interruption and appraise the current interruption performance in simulated systems. A generalized analysis was developed which enabled succinct assessment of the current interruption performance of different thyristor circuit breaker configurations. A 250V, 60A DC Thyristor Circuit Breaker was analysed and a study of TCB-system interaction was made. A novel thyristor circuit breaker switching overvoltage control technique was also investigated. The project findings on TCB-system interaction demonstrated that practical thyristor circuit breaker selection and design must be done in conjunction with the system configuration and its parameters. The normalized and analytical approaches were found to be useful for determining TCB design criteria but computer simulation tools, such as SPICE, are necessary for predicting the full range of TCB current interruption.

Two types of solar cell AlGaAs-GaAs structures which are heteroface and triple heterojunction are investigated in this study. A complete theoretical study including optimisation for the optical properties ( transmission and reflection) of the heteroface Alo.sGao.2As- GaAs space solar cell is presented. The grid shadow and window layer effects, angle of incidence and the effects of the layer design parameters for AR-coating and window layer on the optical properties are considered in the calculations. A new structure for space solar cell which consists of double heterojunction AlGaAs­GaAs structure with GaAs/AlGaAs heterojunction back surface field (triple heterojunction(TIIJ))-to enhance the performance of the existed double heterojunction solar cell- is proposed. The analytical model for this TIU cell is presented as a function of all the cell's design parameters ( such as _layers doping, thicknesses, etc). The calculated results for this structure is compared with the experimental results for the previous double heterojunction structure. The effects of the design parameters of all layers including the AR-coating on the cell's output performance and the optimisation conditions are studied as well. The techniques of the light trapping and the photon recycling( which are gocxl for space solar cells) are applied for the THJ thin film AlGaAs-GaAs structure to improve further the efficiency . The change of the optimisation conditions due to the usage of these two techniques is also discussed.

The research described in this thesis has been carried out in three specific areas, namely the implementation and modification of pitch determination algorithms for speech signals, an investigation of the performance of the algorithms under different conditions of acoustic noise, and the real-time implementation of one of the algorithms using a high speed single-chip digital signal processor. The thesis presents a discussion on the applications of pitch determination algorithms for speech, followed by a description of the mechanism for human production and perception of speech signals. A modelling technique for the speech production mechanism is also introduced. Pitch determination algorithms for speech signals are discussed in detail, with particular reference to the two algorithms implemented during this research. Aspects of their implementation on a digital signal processing system based on an IBM PC-XT and commercially available signal processing software are described. Several important modifications to enhance the algorithms' performance have been carried out, and these are discussed in the thesis. Extensive tests under varying conditions of acoustic noise have been performed, and these are presented in the thesis. Results are presented and discussed, giving an indication of the effect of the noise on the performance of the algorithms. Finally, an implementation of a time domain pitch determination algorithm using a DSP device is presented, with detailed notes on the various aspects of the implementation. Results indicate that using appropriate AID hardware, the algorithm can achieve realtime pitch determination of speech.

The research described in this thesis was carried out in four specific areas, namely, Satellite-Switched Time-Division Multiple-Access (SSTDMA) network synchronisation, frame synchronisers, remote sensing satellite data decommutating systems, and prototype frame synchroniser implementation. In the area of SSTDMA network synchronisation, this thesis reports several new synchronisation methods based on an original on-board synchronisation concept. These new methods are shown to have some significant advantages over existing methods. Also reported is a new algorithm to determine the exact satellite position for the open-loop three ranging stations method. In the area of frame synchronisers, adaptive control strategies and post-detection processing techniques are proposed for a new form of frame synchroniser. This new frame synchroniser is shown to provide reliable and optimum frame synchronisation operation in an unpredictable noisy environment. A high-speed version of the new frame synchroniser is also proposed, and it is shown that the adaptive control strategies may be implemented using a microprocessor-based system. In the area of remote sensing satellite data decommutating systems, this thesis reports a new system. Compared with existing systems, the proposed new system offers greater flexibility and expandability, with data decommutation and distribution carried out in real-time. A prototype adaptive frame synchroniser with post-detection processing was constructed, and tested under various simulated environmental conditions. The design and hardware implementation of the prototype frame synchroniser are described. The abilities of the prototype frame synchroniser, such as various mode transition strategies, automatic polarity correction, bit slippage tolerance up to ±2 bits and a bit error rate (BER) tolerance up to 0.208, were demonstrated via a range of tests, which are described in this thesis.

The research described in this thesis investigates the area of subband coding of high quality digital audio signals. The research into the application of a nonuniform filter bank employing frequency warping to digital audio coding is described. Firstly, some aspects of psychoacoustics, especially masking effects, are studied. Utilising psychoacoustic models, perceptual entropies are calculated for a number of audio excerpts and it is shown that theoretically the bit rate can be reduced to lower than 2 bits per sample. Different types of filter banks are reviewed. To examine the best band splitting scheme, studies are carried out on optimum bit allocations for uniform and nonuniform filter banks, with or without a psychoacoustic model. The concept of perceptual coding gain is proposed and it is shown experimentally that band splitting according to the auditory critical band rate is not recommended for audio compress10n. A new generic nonuniform decomposition algorithm, relying on cascading frequency warping and a uniform filter bank, is developed. Detailed analyses of frequency warped signals are carried out. The effect of truncation of the original signal and the warped signal is investigated. It is shown that the reconstruction is near perfect and coding based on the new nonuniform filter bank is capable of noise shaping. A subband coder based on the nonuniform filter bank is constructed and results are presented. Objective assessment and informal subjective assessment are carried out and they show that the coding reaches high quality at 192 kbps per channel; however, some artefact is perceptable. An efficient implementation of the Koilpillai-Vaidyanathan pseudo-quadrature mirror filter (KVPQMF) bank, which features simplicity in prototype filter design and suitability for audio coding, is developed. The savings in the number of calculations and in the execution time over the direct implementation is significant.

In this thesis the development of a novel descriptor for boundary images represented in a chain code format is reported. This descriptor is based on a truncated series of orthogonal polynomials used to represent a piecewise continuous function derived from a chain code. This piecewise continuous function is generated from a chain code by mapping individual chain links onto real numbers. A variety of alternative mappings of chain links onto real numbers are evaluated, along with two specific orthogonal polynomials; namely Legendre polynomials and Chebychev polynomials. The performance of this series descriptor for chain codes is evaluated initially by applying it to the problem of locating short chains within a long chain; and then extending the application and critically evaluating the descriptor when attempting to match features from pairs of similar images. In addition, a formal algebra is developed that provides the rule base that enables the transformation and manipulation of chain encoded boundary images. The foundation of this algebra is based on the notion that the labelling of the directions of an 8-connected chain code is essentially arbitrary and 7 other, different and consistent labellings can be distinguished.