In this thesis, linear precoding designs and scheduling algorithms are studied based on the maximum Signal-to-Leakage-plus-Noise Ratio (SLNR) criteria in single-cell Multi-user MIMO (MU-MIMO) systems as well as in multi-cell MIMO cooperative networks. The conventional SLNR precoding scheme is firstly investigated. Analytic expressions of the conventional SLNR-based solution are derived and are shown to be a generalised form of regularised channel inversion techniques. Consequently, equivalence between the SLNR and other regularised channel inversion schemes for the case of single-antenna and multi-antenna receivers can be established. This provides an alternative view of the conventional SLNR precoding design and leads to several useful implications in terms of possible exchange of relevant algorithms and performance analysis among these linear precoding schemes. One of the main issues of the conventional SLNR precoding design for the case that all available eignmodes are not fully transmitted is then addressed. Enhanced leakage-based precoding designs are proposed and are thoroughly studied in single-cell MU-MIMO based on two main approaches, i.e. the receive antenna selection and the enhanced receive subspace estimation. The latter is seen to be superior to the former and, as a result, serves as an underlying technique for subsequent studies. The proposed leakage-based precoding designs with receive subspace estimation techniques are further applied to the transceiver design for achieving the maximum Weighted Sum Rate (WSR) in single-cell MU-MIMO systems. Based on the proposed trallsceiver structure, the problem call be simplified into two different problems, i.e. the power allocation and the data stream selection problems, to which the solutions are separately proposed. The resulting precoding designs are shown to have comparable performance to existing joint Transmit (TX)-Receive (RX) filter designs despite requiring simpler receiver structures. The enhanced leakage-based transceiver designs are also extended from the single-cell MU-MIMO systems to multi-cell coordinated beamforming scenarios. Further, the resulting transceiver designs are applied to the WSR maximisation problem in the multi-cell case by extending the power allocation and the data stream selection approaches as previously studied in the single-cell case to the multi-cell coordinated beamforming systems.

Wireless and communication systems are being run at ever increasing in frequencies, but the conventional complimentary metal oxide semiconductor (CMOS) phase locked loop (PLL) architectures are starting to reach a performance limit. A key part of the PLL is the voltage controlled oscillator (VCO) - for this to achieve high frequency performance, low value inductors are required. However, achieving a large tuning range, high Q, and low noise, with these inductors is extremely difficult. This thesis provides a literature review and background to CMOS VCO design, and in particular, using transmission lines as the critical element for generating oscillations. It then goes on to detail the research and development of two test chips, each consisting of eight individual VCOs outputting a differential signal, divided in frequency by four, to dedicated ports on a purpose built printed circuit board. These circuit boards were built using low cost, industry standard materials and the chips tested using standard lab equipment. This project led to the creation of the fastest VCOs ever designed and tested at Fujitsu Semiconductor Europe and highlighted some of the key issues in transforming a technology from a mature academic knowledge into an industrially ready product.

This thesis presents novel results in the field of light manipulation for the purpose of improving lasing in the mid-infrared. It presents comprehensive studies that encompass the design, fabrication, testing and characterisation of nano and microscale plasmonic nanostructures. The main aim of the work is to incorporate nanostructures directly onto the emitting facet of mid-infrared lasers during their fabrication process. The purposes of the structures are to collimate, focus or shape the beam profile of the lasers whilst simultaneously modifying the lasers properties by selecting appropriate feedback radiation reflected into the laser. The thesis introduces the reader to the state of the art in the field of plasmonic nanostructures and the mid-infrared technologies. It then guides the reader through the required background theory before introducing the finite-difference time-domain method, the author's preferred method of simulating nanostructures. Methods of fabricating plasmonic nanostructures are then discussed before as-step Focussed Ion Beam (FIB) milling technique is introduced that can be used for reliable fabrication of features on the nanometer scale (~30nm). A systematic and comprehensive study is presented in chapter 4 of plasmonic nanoantennas. The strong dependency of nanoantennas optical properties on their geometries is explored alongside how they resonantly enhance point-like dipole source emissions. The work then continues to investigate dual resonant plasmonic structures that have the potential to resonantly enhance both the absorption and emission of point-like emitters such as quantum dots and dye molecules. Nanoantenna arrays are then introduced and are designed for the purpose of fluorescent enhancement and focussing in chapter 4. The chapter then presents the successful fabrication process of the nanoantenna arrays and introduces the experimental setups and equipment used to test and characterise them. An analytical model to predict the beamshape of plasmonic nanoantenna arrays is developed and compared to measurements. The comparison shows an extremely good agreement, demonstrating that plasmonic beamshaping has occurred. This chapter also presents a novel way of measuring field enhancement in the presence of both focussing effects and Purcell enhancement. An overall, measured field enhancement of ~50,OOOX is shown in the presence of a plasmonic nanoantenna array. Finally the thesis investigates plasmonic gratings that can be more reliably fabricated as potential lenses for the mid-infrared wavelength region. A standalone lens is shown to collimate laser light and the results are supported by simulation. Chapter 6 then finishes by demonstrating the possibilities of modal selection when fabricated onto the facet of a laser. In this section the 4th TE mode is selected to be reflected back into the laser to undergo gain and become dominant and the measured results are again, predicted by simulation .

Deviating from the archaic communication approach of treating information as a fluid moving through pipes, the concepts of Network Coding (NC) suggest that optimal throughput of a multi cast network can be achieved by processing information at individual network nodes. However, existing challenges to harness the advantages ofNC concepts for practical applications have prevented the development of NC into an effective solution to increase the performance of practical communication networks. In response, the research work presented in this thesis proposes cross-layer NC solutions to increase the network throughput of data multicast as well as video quality of video multi cast applications. First, three algorithms are presented to improve the throughput of NC enabled networks by minimizing the NC coefficient vector overhead, optimizing the NC redundancy allocation and improving the,robustness of NC against bUl'sty packet losses. Considering the fact that majority of network traffic occupies video, rest of the proposed NC algorithms are content-aware and are optimized for both data and video multicast applications. A set of content and network-aware optimization algorithms, which allocate redundancies for NC considering content properties as well as the network status, are proposed to efficiently multicast data and video across content delivery networks. Furthermore content and channel-aware joint channel and network coding algorithms are proposed to efficiently multicast data and video across wireless networks. Finally, the possibilities of performing joint source and network coding are explored to increase the robustness of high volume video multicast applications.

The objective of the work in this thesis is to design lightweight, low profile, circular polarization (CP) antenna technologies which have potential for use in satellite communication systems. A new class of CP Fabry-Perot (FP) cavity antenna which may be used as a replacement for bulky CP horn antennas is developed. A double-sided partially reflective surface (PRS) is employed in the design. The resulting class of antennas are appealing as they allow a specified gain in CP to be achieved while maintaining the simplicity of a single cavity structure and a linearly polarized (LP) primary feed. An example demonstrator antenna with a gain of approximately 21 dB at 15 GHz is designed using the full-wave electromagnetic simulation tool, CST Microwave Studio (MWS). A prototype is produced and measured in order to validate the simulation results. Frequency selective surfaces (FSS) are employed as quasi-optical diplexers in satellite communication systems to facilitate multiband reflector antenna operation therefore allowing multiple feed antennas to share the same aperture. In this thesis quasi-optical diplexers suitable for CP dual frequency band operation are considered. A new class of polarizing surface is developed which in a given frequency band reflects incident linearly polarized waves with circular polarization (CP) while at other frequencies it is transparent allowing incident waves to be transmitted. In addition, a new type of CP FSS which conserves a CP signal upon reflection and transmission is designed. The axial ratio in the reflection and transmission bands is reported for both structures. Numerical EM simulation supported as necessary with analytical analysis is used throughout.

The main objective of this work was the development of the directional modulation (DM) technique, which is a promising keyless physical layer security means for securing wireless communication in free space. It is realized, from a summary of the state-of-the-art OM systems, that although the OM concept appears to be a competitive candidate to enhance the secrecy performance of the next generation of wireless communication, it suffers various fundamental problems, which makes the OM research carried out in an unsystematic and inefficient manner. In order to integrate the previous scattered OM efforts and further pave the path for its applications, in this thesis a theoretical OM framework has been established and some key concepts and OM architectures have been validated via well designed experiments.

Presented here is a novel design for a vertical cavity surface emitting laser for supplying heat to a recording medium in a magnetic recording drive, in an attempt to overcome the superparamagnetic limit. Included in the thesis is a discussion of the requirement for a system to focus energy beyond the diffraction limit and onto a recording platter. Plasmonics is introduced as a method to achieve this focusing and the structure to be used in this work is presented. Initial modelling of the structure for a theoretical efficiency and hence feasibility of the design is then conducted. Fabrication of the device is discussed in detail and preliminary characterisation of the device is undertaken.

This thesis investigates NiFe thin films grown by DC magnetron co-sputtering, with particular emphasis on their suitability as shielding in magnetic recording read heads. Initially, the magnetic, structural and crystallographic properties of NiFe films of varying compositions were investigated, as well as properties of bilayered and multilayered films. Film thickness was kept below a thickness of = 200 nm, as investigation of NiFe film thickness established that at this point samples would appear isotropic due to out of plane anisotropy.

In multi-cell networks where resources are aggressively reused, eliminating interference is the key factor to reduce the system energy consumption. This thesis proposes interference management techniques based on beamforming with different levels of cooperation amongst base stations (BSs). First, a multi-cell beamforming (MBF) technique is introduced to design beamformers as if geographically distributed BSs were a single BS. The aim is to minimise the total transmit power across the network while maintaining the required signal-to-interference-plus-noise ratio (SINR) for every user. An iterative algorithm is proposed to solve the optimisation problem of MBF. Since the MBF scheme requires the circulation of all users’ data amongst coordinating BSs, a user position aware (UPA) algorithm is developed for MBF to reduce the backhaul overhead by allocating each user to nearby BSs only. To completely avoid user data circulation, a semi definite programming (SDP) algorithm, named as coordinated beamforming (CBF), is introduced to jointly calculate beamformers for all coordinating BSs in a manner that each BS transmits to its local users only. Taking into account errors in channel estimations, robust beamforming designs are developed for CBF. Next, fast wireless backhaul protocols, i.e., Star and Ring, are proposed using network coding to enable links amongst coordinating BSs. The maximum achievable throughput of each protocol is analysed. The power consumption of the Ring protocol is characterised and used to compare and evaluate the performance of the proposed beamforming schemes. The deployments of MBF, UPA-MBF and CBF schemes require a central unit for a group of coordinating BSs as well as backhaul links amongst them. In fact, a central unit may not always be available, e.g., in femtocell and self-organising networks, while backhaul links may be limited. Hence, distributed beamforming (DBF) is proposed to independently design beamformers for the local users of each BS. In DBF, the combination of each BS’s total transmit power and its resulting interference power toward other BSs’ users is minimised while the required SINRs for its local users are maintained. SDP and iterative algorithms are introduced to solve the optimisation problem of DBF.

This thesis is concerned with the analysis, design and implementation of multichannel audio systems. The design objective is to reconstruct a given sound field such that it is perceptually equivalent to the recorded one. A framework for the design of circular microphone arrays is proposed. This framework is based on fitting of psychoacoustic data and enables the design of both coincident and quasi-coincident arrays. Results of formal listening experiments suggest that the proposed methodology performs on a par with state of the art methods, albeit with a more graceful degradation away from the centre of the loudspeaker array. A computational model of auditory perception is also developed to estimate the subjects' response in a broader class of conditions than the ones considered in the listening experiments. The model predictions suggest that quasi-coincident microphone arrays result in auditory events that are easier to localise for off centre listeners. Two technologies are developed to enable using the proposed framework for recording of real sound fields (e.g. live concert) and virtual ones (e.g. video-games). Differential microphones are identified as desirable candidates for the case of real sound fields and are adapted to suit the framework requirements. Their robustness to self-noise is assessed and measurements of a third-order prototype are presented. Finally, a scalable and interactive room acoustic simulator is proposed to enable virtual recordings in simulated sound fields.