It is widely known that the Cognitive Radio (CR) paradigm has the potential of improving the exploitation of the earmarked but momentarily unoccupied spectrum, which is exclusively allocated to the primary users (PUs) based on the conventional fixed spectrum allocation policy. The CR systems first have to sense, whether the PU’s band is unoccupied and then dynamically access it. Naturally, CR systems suffer from the same propagation impairments as the traditional wireless communication systems, such as interference, fading and noise, which affect both the reliability and the attainable data rate. In order for the CR system to achieve both reliable data transmission as well as a high throughput and low delay, we propose novel CR-aided Hybrid Automatic Repeat Request (HARQ) protocols, which intrinsically amalgamate the CR functions with HARQ protocols and study their performance. Both perfect and imperfect spectrum sensing are considered. Specifically, we propose the cognitive stop-and-wait-HARQ (CSW-HARQ), cognitive Go-Back-N-HARQ (CGBN-HARQ) as well as the cognitive selective-repeat (CSR-HARQ) schemes and study their throughput and delay both by analysis and simulation. To protect the PUs legal rights, we model their activity of occupying a primary radio (PR) channel as a two-state Markov chain consisting of ‘ON’ and ‘OFF’ states. In order to use the PR channel, the CR system first senses the presence of the PUs and once the PR channel is found to be free (i.e., in the OFF state), the CR system transmits its data packets relying on the principles of SW-HARQ, GBN-HARQ and SR-HARQ. Otherwise, the CR system continues sensing the channel until finding a free one. Naturally, the PR channel may be sensed erroneously, which results either in false alarm or in misdetection. Therefore, the channel may be modelled by a two-state Markov chain, provided that sensing is ideal, or by a four-state Markov chain, if sensing is non-ideal. Here, the four states are determined by the actual state of the PR channel and the state sensed by the CR system. We analyse both the throughput and delay of CR systems relying on different HARQ schemes. We invoke a pair of analytical approaches, namely the probability based approach and the Discrete Time Markov Chain (DTMC) based approach. Closed-form expressions are derived for the throughput, average packet delay and the end-to-end packet delay. Furthermore, for the end-to-end packet delay, we derive both the probability distribution and the average end-to-end packet delay. In the DTMCbased approach, we propose a state generation algorithm for eliminating the illegitimate states, which helps reduce both the dimensionality of the related state transition matrices and the associated computational complexity. All the equations obtained by analysis are validated by numerical simulations. Our performance results reveal that both the achievable throughput and delay of the CSWHARQ, CGBN-HARQ and the CSR-HARQ schemes are substantially affected by the activity of the PUs, by the reliability of the PR channels, by the unreliable sensing decisions and by the number of packets transmitted per time-slot (TS). Specifically, when the probability of the PR channel being busy is high and/or its reliability is relatively low, the throughput attained by these HARQ schemes becomes relatively low and their packet delay increases. Furthermore, for the CGBN-HARQ and CSR-HARQ, our results show that when the propagation environment is time-variant, the number of packets transmitted within a TS should be adapted accordingly, in order to attain the highest throughput and the shortest average transmission delay.

In this thesis, we investigate a suite of transceiver designs for transmission over millimetre wave (mmWave) channels. Furthermore, we conceive the philosophy of Layered Multi-Group (LMG) arrangements relying on the concept of Multi-Functional Multiple- Input Multi-Output (MF-MIMO) systems. More specifically, we propose an amalgam of various MIMO techniques, namely diversity, multiplexing and beamforming techniques as well as Multi-User MIMO (MU-MIMO), user grouping and antenna layering methods, which are capable of simultaneously gleaning various MIMO advantages for the sake of overcoming the unfavourable propagation characteristics of mmWave signals. The mm- Wave channel suffers both from high path loss and sparse scattering, which results in reduced receiver diversity. To mitigate these problems, we propose the LMG Steered Space-Time Shift Keying (LMG-SSTSK) system. More specifically, the LMG-SSTSK system is capable of achieving an enhanced multiplexing gain and an improved diversity gain by relying on STSK, and a beamforming gain with the aid of analogue beamforming. Additionally, LMG-SSTSK is capable of supporting multi-user communication using MU Transmit Precoding (MUTPC) as well as an increased number of served users with the aid of sophisticated antenna layering and user grouping. We opt for STSK as the main transmission scheme, since it is an MF-MIMO, which is capable striking a design trade-off between the achievable throughput and the attainable diversity gain. Additionally, the system employs Orthogonal Frequency-Division Multiplexing (OFDM) for transmitting over the mmWave wideband channel, which imposes frequency selective fading due to its high bandwidth, where time dispersion is imposed by the delay of the sparse multipath components. The above-mentioned antenna grouping and user grouping concepts were introduced into the LMG-SSTSK system in order to overcome the restrictions imposed by the mmWave channel in MU scenarios, where due to the high path loss and the beamforming employed, the system cannot simultaneously support angularly dispersed users. Hence, the users are partitioned into groups and the proposed MF-MIMO communicates with all users by conceiving antenna layering. On the other hand, in order to enhance the LMG-SSTSK’s achievable throughput, we propose the novel Multi-Set Space-Time Shift Keying (MS-STSK) scheme. The MSSTSK system constitutes an improved version of STSK and has the potential of outperforming other MIMO arrangements by appropriately choosing the MS-STSK’s parameters. In MS-STSK, a single dispersion matrix is activated using a classical PSK/QAM symbol and transmitted by activating a single Antenna Combination (AC), where an AC is defined as a unique set of multiple antenna elements out of those available at the transmitter. The achievable throughput of MS-STSK depends on the AC allocation technique employed. Hence, the Distinct Antenna Allocation (DAC) technique and the Shared Antenna Allocation (SAC) technique are conceived. The DAC technique requires a distinct set of antenna elements in each antenna combination, while the antenna elements are shared among the available ACs with the aid of SAC, hence MS-STSK associated with DAC achieves an enhanced performance at the cost of a reduced throughput compared to its SAC counterpart, which strikes a design trade-off between them. Furthermore, in order to transmit over the mmWave channel, we intrinsically amalgamate both OFDM and analogue beamforming with MS-STSK using our OFDM-aided MS-STSK system, leading to our OFDM-MS-STSK system. We further exploit the frequency dimension for enhancing the achievable throughput of the OFMD-aided MS-STSK system by introducing the Multi-Space-Frequency STSK (MSF-STSK) system. Accordingly, we introduce our MU Steered MS-STSK (MU-SMS-STSK) system by employing MU-TPC in OFDMMS- STSK for simultaneously supporting multiple users. Finally, to mitigate the angular selectivity of the beamforming-aided mmWave channel, we reintroduce the LMG structure in the LMG-SMS-STSK arrangement. Additionally, in order to achieve near-capacity performance using the classical MSSTSK scheme, we conceive a serially-concatenated channel coding assisted MS-STSK scheme. More specifically, we devise a soft-decision-aided MS-STSK decoder associated with an iterative two-stage serially-concatenated inner detector and outer decoder, which is designed by relying on EXtrinsic Information Transfer (EXIT) charts. Finally, in order to transmit over the mmWave channel, our soft-decision-aided scheme is combined with wideband techniques, such as OFDM and Single-Carrier Frequency Division Equalisation (SC-FDE), as well as beamforming, where due to the DFT and IDFT mismatch introduced by OFDM, we opt for SC-FDE to retain the advantage of MS-STSK having to rely on a reduced number of RF-chains.

The recent growth in CCTV systems and the challenges of automatically identifying humans under the adverse visual conditions of surveillance have increased the interest in soft biometrics, which are physical and behavioural attributes that are used to semantically describe people. Soft biometrics enable human identification under the challenging conditions of surveillance where it is impossible to acquire traditional biometrics such as iris and fingerprint. The existing work on facial soft biometrics is focused on categorical attributes, while comparative attributes have received very little attention, although they have demonstrated a better accuracy. Thus, it is still unknown whether comparative soft biometrics can scale to large and more realistic databases. Also, the automatic retrieval of comparative facial soft biometrics from images needs to be investigated. The purpose of this thesis is to explore human identification and verification in large and realistic databases via comparative facial soft biometrics using the Labelled Faces in the Wild (LFW) database. A novel set of comparative facial soft biometrics is introduced, and a thorough analysis that assesses attribute significance and discriminative power is presented. Also, a set of identification and verification experiments was conducted to evaluate the comparative facial soft biometrics. Moreover, this thesis proposes MIURank, a novel fully unsupervised ranking algorithm that is based on mutual information. The experiments demonstrate that a correct match can be found in the top 71 retrieved subjects from a database of 4038 subjects by comparing an unknown subject to ten subjects only. Additionally, the experiments reveal that face retrieval by verbal descriptions in a database of images can yield a correct match in the top 15 retrieved subjects from a database of 430 subjects. Furthermore, the performance analysis of the MIURank algorithm shows that it can result in a ranking accuracy that is comparable to the maximum likelihood estimator of Bradley-Terry and the state-of-the-art SerialRank algorithm. By these analyses and developments, it is now possible not only to use human labels for recognition, but also to derive them by computer vision.

Graphene is an atomically-thin 2-dimentional layer of carbon atoms. Since 2004, it has been attracting significant attention for various type of device applications due to its unique properties. In particular, applications of graphene for micro- and nanoscale devices is one of the most demanded and promising research fields. For further advancement of technological flexibility in designing graphene nanodevices, introducing defects to graphene could be a useful method to modify its material properties. Therefore, how to control defects in graphene and how to observe the effects of defects are one of the most important issues. For instance, the defect formed on graphene has been observed to make influence on the charge carrier concentration. Moreover, the defect introduction to graphene will change the phase of the graphene from crystalline to amorphous. Tip-enhanced Raman Spectroscopy (TERS) is a combination of Scanning Probe Microscopy (SPM) and micro-Raman spectroscopy. While micro Raman has played a crucial role to characterise graphene material properties at a microscale level, TERS is considered to be a powerful tool to investigate and characterise nanostructure devices, defect density, and doping with high spatial resolution down to sub 100 nm. In this work my aim is to establish TERS measurement techniques for various types of graphene. Then the TERS is applied for evaluating defect density, edge properties and strain induced in the graphene nanoelectronic and nanoelectromechanical devices to investigate the physics of graphene nanodevices. I have started to optimise the TERS tools on graphene to achieve high spatial resolution. Then I have applied TERS for studying the stress and strain and defect formation on suspended graphene on SiNWs. The result shows that the peak position is shifted in the TERS spectra and additionally the local defects at the edge of SiNW have been observed with a spatial resolution of ~ 100 nm. Then I have introduced defects using helium ion irradiation on graphene nanoribbon (GNR). TERS is used to study the graphene edges and irradiation boundary of in the graphene channels. I have succeeded in taking TERS spectra across the edge of the He-ion-irradiated region on graphene for the first time and confirmed that higher spatial resolution is achievable with TERS.

The demand for low-cost alternatives to conventional point-of-care (POC) diagnostic tools has led to significant developments in the field of microfluidics in porous materials. Several approaches have already been reported for fabricating fluidic devices in such materials, which include photolithography, inkjet printing, wax printing etc. In this thesis, a new approach towards the fabrication of paper-based POC diagnostic sensors is proposed, which is a simple laser-based direct-write (LDW) procedure that uses polymerisation of a photopolymer to produce the required fluidic channels in porous substrates. Furthermore, this LDW technique is also further developed and explored for the introduction of a range of additional functionalities in paper-based microfluidic devices. Firstly, programmable flow control is enabled via two fluid delay mechanisms, namely, permeable barriers with variable porosity and impermeable barriers with variable depth. The generated flow delays can span times from minutes to over an hour. Secondly, the same LDW approach is also developed for stacking and sealing of multi-layer substrates, for assembly of backing layers for two-dimensional lateral flow devices (LFDs) and eventually for fabrication of three-dimensional devices. In addition, we also report an idea of enabling fluidic gating in paper-based devices via triggerable wax barriers. The printed wax barrier acts as triggerable fluidic gates, which can be switched on demand via the application of local heating. Finally, these LDW fabricated paper-based devices were validated via implementation of various clinical diagnostics and analytical chemistry assays using both artificial samples as well as real human bodily fluids. Overall, a huge number of advantages have been established with this approach for both device fabrication and enabling additional functionalities. Thus, we believe that this technique could be an ideal choice for fabrication of paper-based microfluidic devices.

Some of the Heterogeneous Network (HetNet) components may act autonomously for the sake of achieving the best possible performance. The attainable routing performance depends on a delicate balance of diverse and often conflicting Quality-of-Service (QoS)requirements. Finding the optimal solution typically becomes an NP-hard problem, as the network size increases in terms of the number of nodes. Moreover, the employment of user defined utility functions for the aggregation of the different objective functions often leads to suboptimal solutions. On the other hand, Pareto Optimality is capable of amalgamating the different design objectives by relying on an element of elitism. Although there is a plethora of bio-inspired algorithms that attempt to address the associated multi-component optimization problem, they often fail to generate all the routes constituting the Optimal Pareto Front (OPF). As a remedy, we initially propose an optimal multi-objective quantum-assisted algorithm, namely the Non-dominated Quantum Optimization (NDQO) algorithm, which evaluates the legitimate routes using the concept of Pareto Optimality at a reduced complexity. We then compare the performance of the NDQO algorithm to the state-of-the-art evolutionary algorithms, demonstrating that the NDQO algorithm achieves a near-optimal performance. Furthermore, we analytically derive the upper and lower bounds of the NDQO’s algorithmic complexity, which is of the order of O(N) and O(N√N) in the best- and worst-case scenario, respectively. This corresponds to a substantial complexity reduction of the NDQO from the order of O(N2)imposed by the brute-force (BF) method. However again, as the number of nodes increases, the total number of routes increases exponentially, making its employment infeasible despite the complexity reduction offered. Therefore, we propose a novel optimal quantum-assisted algorithm, namely the Non-Dominated Quantum Iterative Optimization (NDQIO) algorithm, which exploits the synergy between the hardware parallelism and the quantum parallelism for the sake of achieving a further complexity reduction, which is on the order of O(√N) and O(N√N)in the best- and worst-case scenarios, respectively. Additionally, we provide simulation results for demonstrating that our NDQIO algorithm achieves an average complexity reduction of almost an order of magnitude compared to the near-optimal NDQO algorithm,while activating the same order of comparison operators. Apart from the traditional QoS requirements, the network design also has to consider the nodes’ user-centric social behavior. Hence, the employment of socially-aware load balancing becomes imperative for avoiding the potential formation of bottlenecks in the network’s packet-flow. Therefore, we also propose a novel algorithm, referred to as the Multi-Objective Decomposition Quantum Optimization (MODQO) algorithm, which exploits the quantum parallelism to its full potential by exploiting the database correlations for performing multi-objective routing optimization, while at the same time balancing the tele-traffic load among the nodes without imposing a substantial degradation on the network’s delay and power consumption. Furthermore, we introduce a novel socially-aware load balancing metric, namely the normalized entropy of the normalized composite betweenness of the associated socially-aware network, for striking a better trade-off between the network’s delay and power consumption. We analytically prove that the MODQO algorithm achieves the full-search based accuracy at a significantly reduced complexity, which is several orders of magnitude lower than that of the full-search. Finally, we compare the MODQO algorithm to the classic NSGA-II evolutionary algorithm and demonstrate that the MODQO succeeds in halving the network’s average delay, whilst simultaneously reducing the network’s average power consumption by 6 dB without increasing the computational complexity.

The thesis reports the development of all-printed actively actuated colour-changing fabrics for creative and smart fabric applications. The colour changing fabrics consist of thermochromic materials and track heaters dispenser printed on fabrics. Thermochromic materials change colour in response to a change in temperature and the heaters actuate the colour change function by controlling the temperature of the fabric. Dispenser printing is a direct-write process where a material is additively deposited on digitally defined locations of the substrate. It is a novel process for printing active and functional materials on fabrics. State of the art thermochromic fabrics use heaters based on conductive yarns, printed circuit boards (PCBs), Peltier semiconductors, conductive coatings and commercial heating foils. These heater technologies have one or more of the four major limitations: inflexibility, limited design freedom, poor integration with fabrics and unreliability. The novel all-dispenser printed approach overcomes the limitations of existing methods by offering flexibility, complete design freedom, good integration with fabrics and reliability. The thermochromic devices are fabricated on 65/35 blend polyester cotton which has a porous and high variation surface. The surface variation of the fabric is numerically characterised and its adverse effect on the electrical properties of printed conductors is experimentally demonstrated. Printing an interface layer on the fabric surface is used as a method of reducing the fabric surface variation. The four evaluated interface inks DuPont 5018, Electra EFV4/4965, Fabinks-IF-UV-1004 and FB-20 reduced the fabric surface variation by more than 95%. This improved the performance of the printed heaters and electrical interconnections on fabrics. This thesis also presents design, modelling, fabrication and characterisation of track heaters. Track heaters are modelled in COMSOL Multiphysics software as a tool to determine the output of a heater design. It is used to derive design rules for printing track heaters. It is demonstrated that dispenser printed track heaters offer complete control of the shape and size of their heat profile. In addition to silver and carbon conductive inks, four custom conductive inks were formulated for printing heaters. The conductive inks achieved a broad range of printed resistivity from 2.43 x 10-7 Ω.m to 1.11 x 10-03 Ω.m. This allows the resistance of an application specific heater design to be varied to suit the requirements of an application. Thermochromic ink development, formulation and characterisation using commercially available materials is discussed. A UV curable thermochromic ink which changed from an opaque black state to a colourless state was achieved. It produced black colour concentration of 90-100 % before colour change and a peak transmittance value of 34% after colour change. It was demonstrated that the optimum ink formulation can be altered to produce a range of colour changing effects such as multiple colour changes which increases the options for thermochromic fabric applications. Fabrication and characterisation of dispenser printed thermochromic devices is also detailed in this thesis. Four demonstrator applications of the thermochromic devices on polyester cotton 65/35 fabric were achieved: a shutter display, a 7-segment display, a matrix display and a proximity controlled interactive thermochromic device. These demonstrators illustrated the freedom of design and versatility offered by the dispenser printed approach. These dispenser printed thermochromic devices can be used in creative applications to produce dynamic art, in smart fabric systems as actuators to communicate data and as non-emissive displays.

Organs-on-chip are a new class of in vitro devices aimed at improving the predictivity of preclinical drug testing models by integrating physiologically relevant features in cell culture devices using microfabrication techniques. In human bodies, epithelial tissues are the first line of defence against the external environment and act as barriers by expressing inter-cellular protein complexes called tight junctions (TJ). The epithelial physical barrier has selective permeability properties which can experimentally be measured by electrical means. In this thesis, the design, simulation, modelling, optimisation, fabrication and experimental characterisation of a novel organ-on-chip device for epithelial cell culture and epithelial barrier monitoring are described. In the device, cells are cultured on top of a nanoporous support, fed by constant perfusion of growth medium and barrier properties are monitored in real-time with integrated coplanar Pt/Pt-black electrodes. Finite element method (FEM) simulations were used to develop a new coplanar electrode design which achieved greater sensitivity (45-fold) compared to the other coplanar designs presented in the literature. This design was formed by 2 circular segments electrodes divided by a polymeric septum. The high sensitivity of the novel electrode design enabled the measurement of epithelial electrical properties directly at the air-liquid interface (ALI) and was used to monitor disruptions in the barrier properties of primary bronchial epithelial cells (PBECs) cultured on commercial supports (Transwell®) induced by a calcium chelator (EGTA). The measured barrier disruption was comparable to those measured by standard systems without requiring a submerged culture. The microfluidic device was used to monitor the establishment of the physical barrier under submerged conditions for 6 days of the human bronchial epithelial cell line (16HBE14o-) and disruption of the physical barrier induced by stimulation with a viral mimic (poly(I:C)). All results were comparable to the ones measured by standard systems. This platform is an easy-to-manufacture alternative to available systems with the unique potential to enable the real-time epithelial barrier monitoring under submerged or ALI conditions.

This thesis presents the work conducted during this project on direct bonding of dissimilar optical materials at the Optoelectronics Research Centre, University of Southampton. It covers the history and background of the art, before progressing to the development of unique bonding processes used during the research detailed. During this project, direct bonding using chemical and plasma activation is successfully conducted on both amorphous and crystalline materials. Bonding of borosilicate glass is demonstrated in the production of planar structured fibre preforms to be caned. Development of Nd:YAG to sapphire bonds is reported, producing bonds of remarkable resilience, capable of surviving dicing and polishing procedures. Zinc selenide to diamond and sapphire bonding is presented using a plasma activated approach along with investigation of the resulting bond’s limits, demonstrating the heat spreading benefits of a bonded diamond layer.

Cloud computing plays an essential role in public organisations and private sector companies, while also reducing the cost of using information technology services. Not only is cloud computing available for users to access anytime and anywhere, but also makes it possible for them to pay for only what they use. In Middle Eastern developing countries, such as Saudi Arabia, cloud computing is still not extensively adopted compared with countries in the West. In order to encourage the adoption of cloud services, this research addresses the essential to investigate the security factors which are associated with cloud computing, and which influence organisations’ desire to adopt the cloud services. Subsequently, this study has developed a theoretical framework that associates security in cloud adoption. In light of the above, the main contribution of this study is the Security Cloud Adoption Framework development in order to support an investigation into the security factors that influence the adoption of cloud computing in KSA government organisations. This research proposes a framework which can be used to understand and evaluate security in cloud adoption; particular emphasis is placed on risks, social aspects, and benefits when implementing security in the cloud services. The proposed framework consists of three categories, namely the Security Social category, the Cloud Security Risks category, and the Cloud Security Benefits category. The framework factors were identified by critically reviewing studies found in the literature, together with factors from the industrial standards within the context of the KSA. The methods used in this confirmatory study were expert interviews and questionnaires. Interviews were conducted with 12 security experts in different Saudi government organisations to confirm the aforementioned factors and to identify those omitted from previous studies. The second method used was questionnaires, which were distributed to 32 IT and security experts from different Saudi government organisations in order to confirm the security factors in the security cloud adoption framework. This framework was subsequently developed. The outcomes from the expert interviews exposed that the proposed security factors in the security cloud adoption framework are statistically significant. In addition to this, the analysis of the interview outcomes and the questionnaire results indicated that there is an additional factor, namely Failure of Client-side encryption, which could potentially affect the adoption of cloud services in KSA government organisations. Experts and security specialists expressed the belief that this factor may influence cloud adoption. The findings of this research were used to improve the suggested framework. Finally, in the validation study, a new instrument was used with 215 IT and security experts in different Saudi government organisations; the purpose of this was to explore the relationship among security factors and to test the model. The instrument was evaluated using a group of experiments; the security experts evaluated the instrument applying the content validity ratio, while the security experts had a part in the validation study. The validation study involved important two tests which examined the internal reliability and the correlation analyses. After applying Structural Equation Modelling (SEM), the resulting data clearly showed a good fit of the structural model and measurement analyses. The key outcomes of the validation study revealed that the relationships among security factors were discovered to have a direct and statistically significant effect in the model. This specifies that the proposed model fits the data and applies to the Saudi context. The contributions of this research are as follows: firstly, it developed a security cloud framework within the KSA context and, secondly, the framework was extended to a security cloud instrument for measurement and validation of the model. Overall, the outcomes of this study are of valuable information in terms of recommendations to cloud providers, government organisations, administrators, and policy makers. Simply put, these findings can assist in the implementation of cloud computing and encourage the spread of this phenomenon across countries in the Middle Eastern, particularly in Saudi Arabia.