This thesis considers theoretical, analytical and engineering design issues relating to non-orthogonal Spectrally Efficient Frequency Division Multiplexing (SEFDM) communication systems that exhibit significant spectral merits when compared to Orthogonal FDM (OFDM) schemes. Alas, the practical implementation of such systems raises significant challenges, with the receivers being the bottleneck. This research explores detection of SEFDM signals. The mathematical foundations of such signals lead to proposals of different orthonormalisation techniques as required at the receivers of non-orthogonal FDM systems. To address SEFDM detection, two approaches are considered: either attempt to solve the problem optimally by taking advantage of special cases properties or to apply sub-optimal techniques that offer reduced complexities at the expense of error rates degradation. Initially, the application of sub-optimal linear detection techniques, such as Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE), is examined analytically and by detailed modelling. To improve error performance a heuristic algorithm, based on a local search around an MMSE estimate, is designed by combining MMSE with Maximum Likelihood (ML) detection. Yet, this new method appears to be efficient for BPSK signals only. Hence, various variants of the sphere decoder (SD) are investigated. A Tikhonov regularised SD variant achieves an optimal solution for the detection of medium size signals in low noise regimes. Detailed modelling shows the SD detector to be well suited to the SEFDM detection, however, with complexity increasing with system interference and noise. A new design of a detector that offers a good compromise between computational complexity and error rate performance is proposed and tested through modelling and simulation. Standard reformulation techniques are used to relax the original optimal detection problem to a convex Semi-Definite Program (SDP) that can be solved in polynomial time. Although SDP performs better than other linear relaxations, such as ZF and MMSE, its deviation from optimality also increases with the deterioration of the system inherent interference. To improve its performance a heuristic algorithm based on a local search around the SDP estimate is further proposed. Finally, a modified SD is designed to implement faster than the local search SDP concept. The new method/algorithm, termed the pruned or constrained SD, achieves the detection of realistic SEFDM signals in noisy environments.

Location systems developed for indoor environments have attracted increasing interest, as a result of the rapidly growing location and navigation services provided by the Global Positioning System (GPS). Location information of people and objects can be used to cooperate with existing communication or database systems to provide abundant services to system operators and end users. For example, equipment tracking in hospitals ensure that location of the appropriate equipment can be provided simultaneously with necessary medical services; attendee tracking at conferences may encourage more efficient communications and networking; location of valuable assets in factories or warehouses aids logistics and protects these assets from theft. Since established global and terrestrial navigation systems cannot provide reliable location services in indoor environments, these demands are increasingly being met by wireless indoor location systems. A review of the existing systems reveals that the current systems are able to provide either an accurate location service with sophisticated system design at higher cost or a less accurate location service by means of integrated systems supplemented by existing facilities. This thesis presents a novel design of an indoor location system that is based on an RF-over-fibre backbone network, which is able to provide high location accuracy while the network infrastructure can be shared with multiple wireless systems. It is the first such demonstrator in this area. This research has been conducted by the author through a research project called The Intelligent Airport (TINA), which is the motivation for this research. The TINA project seeks to develop a new seamless wireless/wired ubiquitous infrastructure with high levels of computational capability to meet the application requirements of future airport environments. In the TINA system, multiple wireless services are provided through an integrated system supported by an RF-over-Fibre network, which transports RF signals through optical fibres. The active RFID indoor location unit is an essential part of the TINA system, which will facilitate the infrastructure to provide location-based services. The thesis describes the detailed design of the active RFID indoor location system proposed for the TINA project, and a few key issues discovered during trials of the demonstration system developed. The overall system design, including ranging technique, TDOA location finding algorithm, and hardware implementation, is presented in this thesis. Particular contributions also include a numerical algorithm for solving target location from TDOA measurement and a technique to determine the chirp linearity requirement. The field trial results of the system design demonstrate the principals and their location performance. The system has the potential to be extended to other scenarios where RF-over-fibre networks are employed and accurate location ability is desired.

In this thesis, a comprehensive analytical and numerical study of optical non-linear effects in plasmonic metamaterials is presented. The new results reported and described in this work can potentially have a significant impact on our understanding of electromagnetic phenomena in artificial optical materials, and facilitate the design and fabrication of new active optical devices with new or enhanced functionality. Equally important, these results could lead to deeper physical insights into the fundamental properties of these metamaterials. To this end, a new analytical formalism based on the multiple scattering theory has been developed, a theoretical framework that allows one to fully characterise the linear and non-linear electromagnetic properties of arbitrary distributions of metallic nanowires. This formalism is unique in allowing readily retrieval of the spatial distribution of the electromagnetic field both at the fundamental frequency (linear analysis) and the second harmonic (non-linear optical response). The formalism also allows for both frequency- and time-domain investigations. Based on this work, a new software tool with unique features has been implemented and used to achieve a better understanding of the intricate electromagnetic phenomena occurring in nano-structured plasmonic systems. In particular, this tool has been used to design and investigate numerically several new non-linear plasmonic structures and nanodevices with remarkable properties. Amongst them were non-linear plasmonic cavities with high quality factors, plasmonic cavities that support non-linear whispering gallery modes and sub-wavelength non-linear plasmonic sensors with enhanced sensitivity and reduced device volume. Several other plasmonic systems that show tremendous potential for the development of advanced metamaterials-based devices have also been explored. Specifically, it was demonstrated that nano-patterned metasurfaces can be employed to achieve polarisation controlled electromagnetic response in arrays of cruciform apertures and magnetisation induced second harmonic generation in chiralmetallic structures. The numerical investigation of photonic superlattices exhibiting zero effective index of refraction has also been discussed.

End-point detection for deep reactive ion etch of silicon in the semiconductor industry has been investigated with a focus on statistical treatments on optical emission spectroscopy. The data reduction technique Principal components analysis (PCA) has been briefly reviewed and analysed as an introduction to independent component analysis (ICA). ICA is a computational dimension reduction technique capable of separating multivariate data into single components. In this instance PCA and ICA are used in to combine the spectral channels of optical emission spectroscopy of plasma processes into a reduced number of components. ICA is based on a fixed-point iteration process maximizing non-gaussianity as a measure of statistical independence. ICA has been shown to offer an improvement in signal to noise ratio when compared to principal component analysis, which has been widely used in previous studies into end-pointing. In addition to the end-point investigation, a study was carried out into the fabrication of arrays of free standing silicon nanorods. The fabrication process consisted of an electron beam lithograpy stage to pattern bare silicon, followed by a deep reactive ion etch - using the Bosch process - to create the nanorods. A variety of difference diameter nanorods, with a selection of pitch dimensions were created using this technique.

This thesis develops new approaches for distributed coordination of data-intensive communications between wireless sensor nodes. In particular, the topic of synchronization, and its dual primitive, desynchronization at the Medium Access Control (MAC) or the Application (APP) layer of the OSI stack, is studied in detail. In Chapters 1 and 2, the related literature on the problem of synchronization is overviewed and the main approaches for distributed (de)synchronization at the MAC or APP layers are analyzed, designed and implemented on IEEE802.15.4- enabled wireless sensor nodes. Beyond the experimental validation of distributed (de)synchronization approaches, the three main contributions of this thesis, corresponding to the related publications found below, are: • establishing for the first time the expected time for convergence to distributed time division multiple access (TDMA) operation under the two main desynchronization models proposed in the literature and validating the derived estimates via a real-world implementation (Chapter 3); • proposing the extension of the main desynchronization models towards multi-hop and multi-channel operation; the latter is achieved by extending the concept of reactive listening to multi-frequency operation (Chapter 4 and 5). • analyzing the energy consumption of the distributed TDMA approach under different transmission probability density functions (Chapter 6 and 7). Conclusions and items for future work in relation to the proposals of this thesis are described in Chapter 8.

With the rapid development and deployment of 802.11 wireless network signals over recent years, wireless network transmission has become widely available in many public places. This has given rise to interest from many researchers in application of these systems to detection and tracking. However, the majority of this research is focussed on co-operative detection using base station signal triangulation methods. There has been little research on non-cooperative indoor detection using wireless communication signals. This dissertation offers a comprehensive study of non-cooperative passive bistatic wireless detection methods. This includes a review of the literature, and a detailed theoretical and experimental study to evaluate the performance of the performance of bistatic passive radar (PBR) using wireless signals as an illuminator of opportunity. The characteristics of 802.11 wireless LAN signal were investigated, including the modulation scheme, the effective bandwidth, and the shifting transmission rate, which all influence and contribute to passive radar performance. The bistatic range resolution is 27 m when there is a lower transmission rate (1 Mbps and 2 Mbps) using DSSS PHY (with 11 MHz bandwidth); and the bistatic range resolution is 15 m when there is a higher transmission rate (above 5 Mbps) using OFDM PHY (with 20 MHz bandwidth). The ambiguity functions of typical waveforms of the 802.11 wireless LAN signals were simulated and analyzed from the radar perspective after the investigation of the communication signal characteristics. The echo power performance was then investigated as the initial experiment using the 802.11 beacon signal in an anechoic chamber and real wireless data transmissions in an office environment. The measurements seemed to agree quite closely with the theoretical values in an ideal environment. A comprehensive range of experiments in both indoor and outdoor environments were then conducted to examine the range and Doppler detection performance. These experiments demonstrated the first reported results for non-cooperative detection of human and other targets using wireless transmissions. Performance bounds were determined from these experiments and direct and multipath signal suppression identified as key areas to improve performance. Direct signal interference cancellation methods based on an adaptive filter were therefore developed and verified with effective cancellation results. The adaptive filter method developed in this study improved target SIR by about 30 – 40 dB. This study was finally extended to consider longer range outdoor detection using 802.16 (WiMax) transmissions. Simulations were carried out for real maritime surveillance scenarios and compared with existing active radars. This preliminary study showed that wireless based passive radar has the potential to replace active systems in some scenarios and is the subject of ongoing studies.

The use of opto-electronic devices for ultrafast switching applications is a practical alternative to all electronic devices due to their operating ceiling. The harnessing of femto-second laser pulses to momentarily switch devices has been the centre of research for over twenty years since the pioneering work of Auston. Though the design of the electrodes of an Auston switch has not altered to any great effect, the light absorbing material has been the primary occupation of researchers. The ultrafast behaviour of these materials is due to the sub picosecond quenching of photogenerated carriers caused by deep trapping levels pinned between the valence and conduction bands of the material. The creation of these carrier traps is due to the presence of non-stoichiometric features in the semiconductor lattice structure. There have been several attempts to create such material. Originally based on Silicon on Sapphire materials, the most successful ultrafast photoconductors were found to be low temperature grown Gallium Arsenide. However this large bandgap material requires cumbersome gas or titanium sapphire lasers as the pulsed light source. Of great interest are the Indium Phosphide based materials which can harness the 1550 nm wavelength technology of optical telecommunications where erbium fibre and solid state mode-locked lasers have been developed which are low cost, compact and could enable on-chip integration. One successful approach to achieve 1550 nm absorbing ultrafast photoconductors has been the use of high energy ion irradiation of Indium Gallium Arsenide (In0.53Ga0.47As) lattice matched to Indium Phosphide substrates. There has been research of proton and heavy ion irradiation of 1550 nm wavelength absorbing materials; but no ultrafast switching devices have been fabricated from lighter ion irradiation. The advantages of this method are the higher defect concentrations achievable compared to proton irradiation and the minimising chemical changes to the material substrates which have been observed with heavy ion irradiation. The implanted ion chosen in this project was Nitrogen because of its mass and inert behaviour. In order to demonstrate the ultrafast behaviour of the Nitrogen ion implanted InGaAs, and to show that it is a practical alternative to LT-GaAs based devices, a set of ultrafast photoconductive sampling switches were designed, fabricated and evaluated. This thesis describes the design, fabrication and evaluation of InP based ultrafast switches capable of sampling waveforms up to 20 GHz. The principle mechanisms involved in the ultrafast quenching of photocarriers was investigated and the optimum design for the photoconductive switch determined. An equivalent circuit of the switch was devised and its expected performance modelled with regard to the on and off state resistances. Using transform mapping techniques, the switch capacitance and waveguide dimensions were calculated. The switches were fabricated using wet etching and metal lift-off techniques prior to evaluation of the pre-irradiated devices. Once the expected behaviour of the pre-implanted switch had been characterised, the switches were implanted by high energy nitrogen ions. These implanted devices were then evaluated and their ultrafast characteristics confirmed. With a carrier recombination time of 5 picoseconds (FWHM) being measured, this is the first time that deep nitrogen implantation has been used to create ultrafast InP based switches.

In this thesis, we present an intensive investigation on the analytical models to describe the field-effect mobility, the current-voltage (I-V) characteristics, and the instability mechanisms in oxide TFTs, e.g. amorphous In-Ga-Zn-O TFTs. Here, we considered the unique material properties and underlying physics of it, such as the localized tail states, the potential barriers, and the oxygen vacancies. The derived mobility model and the I-V relation for oxide TFTs have been proposed for the first time, yielding a physically-based transistor model for the circuit design and simulation. Also, we developed an analytical method to extract the localized tail state profile to be used as a basis to derive those mobility and I-V models. Here, the relationship between the Fermi-level and gate voltage is derived analytically for the gate voltage-dependent expressions of each model. These models were simulated and compared with the experiments, providing a good agreement with each other. Regarding the instability study, we developed a quantitative analysis on the photoconductive gain due to the oxygen vacancy ionized under illumination, and proposed a gate-pulse spectroscopy to get the ionized oxygen vacancy profile in energy. These studies suggest a visible light sensor application to be embedded into a display panel, e.g. an interactive display, intentionally using the oxygen vacancy-rich layer, e.g. the In-Zn-O, incorporated into a bi-layer channel photo-TFT structure. Consequently, a complete analysis on device physics and modelling of the oxide TFTs is presented in this thesis, providing analytical and quantitative insights into the physics of the oxide TFTs, and their potential for future interactive and transparent electronic systems.

Quality Directors, aware that poor quality causes software project failure wasting billions worldwide, need to implement strategies that minimise costs, are practical and scalable. This is especially important in communications systems software where failures can lead to loss of service and consequential loss of revenue. This research examines relevant development models, standards and literature, often having conflicting biases, merits and drawbacks. A new model, driven by quality, is proposed in this thesis taking an amalgam of the best features and practices by reexamining the definitions of quality and the anatomy of software development from a quality perspective. The key practices and tools necessary to drive the minimisation of defect injection and maximise defect discovery are studied and a new quality model developed. To avoid overlap and gaps, the filtered defect types for each of the practices and tools are examined and crucially appropriate metrics applied. The metrics are critically selected and emerging new tools enabling more efficient defect discovery and metrics are considered. The new model, termed ‘the defect filtration process’, is made relevant and visible to the whole organisation by ensuring that poor quality is not only measured in the currency of the number of defects discovered by customers, but in the estimated costs and progressive savings trends. Highly visible, organisationally aligned, efficient and stakeholder-relevant metrics are published and presented to the entire organisation including the Board. The metric development process is generic and shown to be relevant not only to software development but the entire maintenance phase. The effectiveness of the new model is demonstrated using a 3G small-cell case study where the cost savings in the first 9 months of implementation amounted to over £1.5M. The case study also illustrates the extensibility of the model where there is complexity and exacting performance demands from the telecommunications industry.

Multiple-input multiple-output (MIMO) antenna systems have been shown to be able to substantially increase date rate and improve reliability without extra spectrum and power resources. The increasing popularity and enormous prospect of MIMO technology calls for a better understanding of the performance of MIMO systems operating over practical environments. Motivated by this, this thesis provides an analytical characterization of the capacity and performance of advanced MIMO antenna systems. First, the ergodic capacity of MIMO Nakagami-m fading channels is investigated. A unified way of deriving ergodic capacity bounds is developed under the majorization theory framework. The key idea is to study the ergodic capacity through the distribution of the diagonal elements of the quadratic channel HHy which is relatively easy to handle, avoiding the need of the eigenvalue distribution of the channel matrix which is extremely difficult to obtain. The proposed method is first applied on the conventional point-to-point MIMO systems under Nakagami-m fading, and later extended to the more general distributed MIMO systems. Second, the ergodic capacity of MIMO multi-keyhole and MIMO amplify-and-forward (AF) dual-hop systems is studied. A set of new statistical properties involving product of random complex Gaussian matrix, i.e., probability density function (p.d.f.) of an unordered eigenvalue, p.d.f. of the maximum eigenvalue, expected determinant and log-determinant, is derived. Based on these, analytical closedform expressions for the ergodic capacity of the systems are obtained and the connection between the product channels and conventional point-to-point MIMO channels is also revealed. Finally, the effect of co-channel interference is investigated. First, the performance of optimum combining (OC) systems operating in Rayleigh-product channels is analyzed based on novel closed-form expression of the cumulative distribution function (c.d.f.) of the maximum eigenvalue of the resultant channel matrix. Then, for MIMO Rician channels and MIMO Rayleigh-product channels, the ergodic capacity at low signal-to-noise ratio (SNR) regime is studied, and the impact of various system parameters, such as transmit and receive antenna number, Rician factor, channel mean matrix and interference-tonoise- ratio, is examined.