The main aim of this work is to demonstrate that communication-type equipment systems can effectively be simulated on a digital computer. A time domain digital simulator ICOSS is first developed. ICOSS provides a facility for interactive simulation of most receiver/transmitter types of communication structure, by specifying individual signal processing modules, each of which can be described mathematically. Simulation using ICOSS operates interactively where the user can construct, edit, change some of the parameters, run the program and look at the result in one simulation session. ICOSS, being a time domain digital simulator is capable of handling feedback operation and stochastic processes. The examples of simulation in this thesis are more inclined towards solving some of the practical problems encountered in developing certain communication equipment systems. The work also includes the investigation by computer simulation of some practical problems which are difficult or impossible to measure effectively in practice, but which can be investigated by means of computer simulation. The simulation results clearly show that system studies by simulation provide a simple and effective approach to system design before the final system is actually built in the laboratory. In the simulation process, the analytic signal lowpass equivalent is used because it is a powerful and cost effective modelling technique for communication system. The thesis begins in chapter one with the introduction of the modelling concept and various areas of simulation that can be applied in communication. Chapter two describes briefly the theory and operation of the phase locked loop and its fast acquisition technique, which are used in the simulation work of later chapters. Analytic signal and lowpass equivalent modeling techniques used throughout the simulation work are demonstrated at the beginning of chapter three. Chapter three also introduces ICOSS - the time domain interactive Communication System Simulator, developed at the School of Electrical Engineering, University of Bath. Its structure, implementation and operation are described. The development of ICOSS is tested by simulating practical systems, that is, a phase locked loop and its fast acquisition technique, and comparing the simulation and practical results as implemented in chapter four. The significance of the sampling frequency in computer simulation, and subsequently its effect on computer processing time and cost is also demonstrate in chapter four by carrying out various simulation tests. One of the main aims of modelling is to model a system with the minimum number of sample points, in order to reduce the amount of computation and hence valuable computing time. Chapter five investigates by simulation the effect of noise, a typical example of a stochastic process, on the performance of the phase locked loop and its fast acquisition loop. The results are compared with practical measurements. In a practical case, it is difficult to monitor and measure the loop performance at low signal to noise ratios, but it can be performed easily by using computer simulation. Chapter six simulates the effect of time delay on the acquisition performance of the phase locked loop and its fast acquisition technique. The effect of delay in the loop is particularly important because it is difficult and almost impossible to investigate effectively in a practical system. Chapter seven concludes by summarising the work and results of simulation of the preceding chapters, including future development of ICOSS. Appendix A provides a brief instruction guide to the use of ICOSS for future users.

The advantages of series capacitor compensated lines in long distance transmission are well known. There are, however, problems encountered in the protection of such lines and these basically arise because, under faulted conditions, the primary system parameters are often subjected to rapid changes due largely to capacitor protective gap operation. The successful longer term development of new transmission line protection techniques is heavily dependent upon a detailed knowledge of the behaviour of practical compensated e.h.v. feeder configurations. In this thesis methods have been developed for accurately simulating the responses of series compensated system using digital simulation techniques based on frequency domain methods. The digital simulation of practical series compensated systems with shunt reactors has hitherto presented a particularly difficult problem. This thesis highlights these problems and outlines the basis of the techniques which have been developed to overcome them. In particular, the basis of some of the novel techniques developed for simulating the essentially random nature of series capacitor spark gap operation together with the non-linearities associated with single pole autoreclosure techniques has been explained. Interesting results relating to the responses of a practical 500 kV long distance transmission interconnection and its effect on the performance of modern distance protection has been presented. By examining the performance of the present day distance protection as applied to series compensated lines with spark gap operations, this work has contributed to the solution of a major problem associated with such lines.

This thesis is concerned with the properties of a particular discrete transform, and its applications to the classification of multi-valued ("m-ary" ) logic functions and m-ary combinatorial logic analysis and synthesis. The transform used is composed of a complete set of orthogonal functions, namely Chrestenson Functions, and the methods developed are applicable for all m, m = 2, 3, ... . The definition of multi-valued systems and some examples of multivalued circuits are given in chapter 1. The necessity of a generalised design method which is not based on a particular algebra is considered and the scope of the thesis is stated. Chapter 2 introduces the algebraic notation, and continues to show the expansions of fully specified m-ary functions in (i) Lagrange form, (ii) generalised Reed-Muller form, and (iii) as polynomials' over the field of real numbers. Chapter 3 is an application of the mathematical developments covered in the previous chapter. Based on generalised Reed-Muller coefficients a realisation of m-ary functions using Universal-Logic-Modules is described. The realisation in this case is restricted to m being a power of a prime. The complex polynomial expansion of m-ary functions is considered in chapter 4. The coefficient set obtained is termed the "spectrum" of the given function. The effects of various operations in the function domain on the spectral values are investigated, and a classification of m-ary functions is described. Applications of spectral properties developed for m-ary combinatorial logic design are shown in examples. The implementation of any m-ary function involves some form of decomposition using physically available logic functions. The spectral properties developed in chapter 4 are further pursued in chapter 5 with an investigation into the relationships between the spectra of the logic functions involved in such a decomposition, and the spectrum of the overall function being realised. With the development of these spectral decomposition relationships, the range of tools for the spectral analysis of m-ary combinatorial logic is completed. Throughout this thesis emphasis is placed on the generality of techniques developed, such that these techniques may be applicable to whatever higher-valued logic microelectronic circuit realisations may evolve in the future.

Time encoded speech (TES) proposes the transmission of speech by segmenting the waveform between real-zero crossings. Speech comprises two types of sound - voiced and unvoiced. The segment rate is low for voiced sounds and high for unvoiced sounds. Matching of the variable segment generation rate to the constant transmission rate is achieved by inserting storage buffers. Since the variation in generation rate can be large for a particularly fricative utterance, the storage buffer has to be large, and consequently, the delay in transmission is large. This thesis presents a technique which reduces the buffer size requirements and hence the delay in transmission. The technique, hybrid-TES, achieves these reductions by identifying the high segment generation regions of the speech waveform; and by storing and transmitting special symbols to indicate the reconstruction of these regions by spectrally shaped random noise.

Thesis (M.A.)--Boston University

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Over the last few years, the non-volatile memories (NVM) have been dominating the research of the storage elements. The resistance random-access memory (RRAM) and the memristor that employs the resistive switching (RS) mechanism appear to be potential candidates for NVM. Among the RS materials that were reported is the TaOx which showed surprising RS performance. This oxide material has been widely used to construct a metal-insulator-semiconductor-metal (MISM) RRAM which can be referred to as bi-layered RRAM. This bi-layered RRAM consists of TaOx as a bulk material and Ta2O5 as an insulator layer, sandwiched between two platinum electrodes to form Pt/Ta2O5/TaOx/Pt RRAM. However, a physics-based mathematical model of this RRAM is required to further study the detailed physics behind its conduction mechanism and the RS process. In addition to the mathematical model, a SPICE model is also required to understand the behaviour of this bi-layered RRAM device when integrated in memory design for the future generation storage devices or when used in RRAM-based circuit applications. This doctoral research presents novel mathematical and SPICE models of a bipolar resistive switching (BRS) of the Pt/Ta2O5/TaOx/Pt bi-layered RRAM. For this purpose, MATLAB and LTSPICE are used to design the mathematical and the SPICE bi-layered RRAM models, respectively, and the obtained simulation results for both models are compared with the experimental data from SAMSUNG labs. The novelty of the mathematical model lies in incorporating the tunnelling probability factor (TPF) between the semiconductor and the metal layers and therefore, demonstrating its effect on the conduction mechanism. In addition, the effect of continuous variation of the interface traps densities and the ideality factor during BRS is modelled using the semiconductor properties and the characteristics of the metal-insulator-semiconductor (MIS) system. Thus, the model emphasizes the dependency of the device current on the physical characteristics of the insulator layer. Moreover, the electric field equation for the active region is derived for the MISM structure which is used together with Mott and Gurney rigid point-ion model and Joule heating effect to model the oxygen ion migration mechanism. Finally, the model also demonstrates the self-limiting growth of the doped region. The proposed SPICE model emphasizes the impact of the change in the switching layer thickness on the device behaviour at low resistance state (LRS), high resistance state (HRS), and the transitional period. The validity of the SPICE model is verified through using three different sets of experimental data from Pt/Ta2O5/TaOx/Pt RRAM with switching layer thickness smaller than 5 nm. The SPICE model reproduced all the major features from the experimental results for the SET and RESET processes and also the asymmetric and the symmetric characteristics in HRS and LRS, respectively. The SPICE model matches the measured experimental results with an average error of < 11%. It also showed stable behaviour for its HRS and LRS regions under different types of input signals. The model is parameterized in order to fit into Ta2O5/TaOx RRAM devices with switching layer thickness smaller than 5 nm, thus, facilitating the model usage. The SPICE model can be included in the SPICE-compatible circuit simulation and is suitable for the exploration of the Ta2O5/TaOx bi-layered RRAM device performance at circuit level. At the end of the research, a metal-insulator-metal (MIM) RRAM SPICE model of Ta/TaOx/Pt is developed which can be used in the future work to compare between the MISM and MIM TaOx-based RRAM devices.