The purpose of localization and tracking technology in indoor application is to extract moving object parameters accurately and precisely. This thesis investigates the problem of how to utilize RFID technique for the accurate and precise extraction of indoor 2D moving object position parameters. Firstly, a framework named RFID-Loc with three modules: RFID-Loc Infrastructure, RFID-Loc Data Filter and RFID-Loc Localisation Algorithm, is established from a theoretical perspective. This framework can guide the research and design of methods used in an RFID based object localisation system with enhanced localisation accuracy and precision. Secondly, from practical perspective, few methods are proposed in RFID-Loc framework to improve the localisation accuracy and precision. A sparse RFID Tag Arrangement strategy is proposed in this RFID-Loc framework, aiming at reducing the impacts of regular false reading error from RFID infrastructure level on localisation precision. The efficiency of this methods and the assumptions upon which it relies, are investigated empirically. A rectangle-based feature selection method is justified as the major RFID Data Filter algorithm, with the capability of maximally reducing regular false reading errors. The possibility to resist unexpected false reading error in an RFID-Loc system is investigated by discussing and comparing several RFID-based localisation algorithms. A dynamic localisation algorithm for RFID-Loc system is proposed to accurately and precisely extract moving object position parameters overtime in an RFID-Loc system. This algorithm is shown to have a better capability of resisting unexpected false reading error than conventional localisation algorithms used in RFID-based localisation systems, while having a higher computational complexity. By following the theoretical guidelines in RFID-Loc framework and implementing the proposed methods, the experimental results demonstrate that the localisation accuracy and precision can be significantly improved, up to 10 centimetres and 3 centimetres under current RFID devices.

In order to satisfy the ever increasing demand for the bandwidth requirement in broadband services the optical orthogonal frequency division multiplexing (OOFDM) scheme is being considered as a promising technique for future high-capacity optical networks. The aim of this thesis is to investigate, theoretically, the feasibility of implementing the coherent optical OFDM (CO-OOFDM) technique in long haul transmission networks. For CO-OOFDM and Fast-OFDM systems a set of modulation formats dependent analogue to digital converter (ADC) clipping ratio and the quantization bit have been identified, moreover, CO-OOFDM is more resilient to the chromatic dispersion (CD) when compared to the bandwidth efficient Fast-OFDM scheme. For CO-OOFDM systems numerical simulations are undertaken to investigate the effect of the number of sub-carriers, the cyclic prefix (CP), and ADC associated parameters such as the sampling speed, the clipping ratio, and the quantisation bit on the system performance over single mode fibre (SMF) links for data rates up to 80 Gb/s. The use of a large number of sub-carriers is more effective in combating the fibre CD compared to employing a long CP. Moreover, in the presence of fibre non-linearities identifying the optimum number of sub-carriers is a crucial factor in determining the modem performance. For a range of signal data rates up to 40 Gb/s, a set of data rate and transmission distance-dependent optimum ADC parameters are identified in this work. These parameters give rise to a negligible clipping and quantisation noise, moreover, ADC sampling speed can increase the dispersion tolerance while transmitting over SMF links. In addition, simulation results show that the use of adaptive modulation schemes improves the spectrum usage efficiency, thus resulting in higher tolerance to the CD when compared to the case where identical modulation formats are adopted across all sub-carriers. For a given transmission distance utilizing an artificial neural networks (ANN) equalizer improves the system bit error rate (BER) performance by a factor of 50% and 70%, respectively when considering SMF firstly CD and secondly nonlinear effects with CD. Moreover, for a fixed BER of 10-3 utilizing ANN increases the transmission distance by 1.87 times and 2 times, respectively while considering SMF CD and nonlinear effects. The proposed ANN equalizer performs more efficiently in combating SMF non-linearities than the previously published Kerr nonlinearity electrical compensation technique by a factor of 7.

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 4th generation- long term evolution (4G-LTE) mobile technology is widely adopted that offer both higher capacity and efficient bandwidth usage at a global level. However, considering that in cellular networks the major data traffic mostly occurs indoor, providing high quality can be a daunting task. 4G-LTE provides strong support for both outdoor and indoor coverage by adopting enhanced NodeB (eNB) and home eNB (HeNB), respectively. This research work presents (i) a single-mode filtering technique (SMFT) as a simple design, low cost scheme to degrade the dispersion behaviour of the hybrid radio over the multi-mode fibre (MMF) and free space optics (RoMMF-FSO); (ii) the hybrid radio-over-fibre and radio-over-FSO (RoF-FSO) system as a solution to extend the indoor coverage of 4G-LTE; and (iii) the use of perfluorinated graded-index polymer-optical fibre (PF-GI-POF) for in-building networks. The results show that SMFT may increase RoMMF-FSO bandwidth by 2 GHz and enhance the error vector magnitude (EVM) performance by 4%. The proposed system was also made to experience weak turbulence and thick fog for transmission of 67.2 Mbps 16-QAM 4G-LTE. A design for the residential gateway is proposed as the interface between the 1550 and 850 nm wavelengths. The 100 m of PF-GI-POF is adopted as in-building network with 4G-LTE being transmitted over the proposed hybrid radio-over-POF and FSO (RoPOF-FSO) link under the thick fog condition. The proposed system can transmit 4G-LTE at a data rate of up to 33.6 Mbps and 100.8 Mbps, with the latter encountering a power penalty of ~8 dB to compensate for the induced fog loss. Furthermore, the successful transmission of 60 Mbps at 2.6 GHz was reported to have achieved the EVM of 3.5% and BER 10-5 for 300 m of PF-GI-POF.

Free space optical (FSO) communication provides high speed data communications with high flexibility and cost-effectiveness. However, FSO links are sensitive to atmospheric effects such as fog, smoke and turbulence. To address the problem, this research is investigating a hybrid FSO and RF technology to ensure link availability under all weather conditions as part of the last mile access networks. The research exclusively investigates design, implementation, and assessment of a novel dual purpose hybrid FSO/RF antenna. The technical issues are interference between FSO and RF parts; compactness of the design; quality of service; and robustness. As part of the design a conventional RF antenna scheme, known as Cassegrain antenna is adopted, and a new design scheme for a hybrid antenna is proposed. For the FSO part an optical transceiver aperture, which is composed of optical lenses and optical fibres, is designed and incorporated in the shadowing region of the sub-reflector of Cassegrain antenna. The use of lens and fibre ensures the isolation between the optical and RF parts. Based on the initial design, modifications are made to enhance the hybrid antenna performance. In this work the focus of the research is on the optical part and how it is incorporated as part of the RF antenna. As part of the optical design, spatial diversity and differential signalling techniques are adopted. Majority-logic combining is adopted from RF technology and the performances of a FSO system implementing combining methods are compared for various turbulent regimes. The concept of differential signalling is investigated in terms of the channels correlation and it is shown that the variation of the detection threshold level reduces in correlated channels. A new design method is given based on spatial diversity and differential signalling techniques. To simulate the RF part, CST STUDIO SUITE® software is used, whereas Monte-Carlo simulation is used for performance estimation of the FSO link. Also provided are the detailed mathematical modelling of the hybrid FSO/RF system. The proposed hybrid antenna is fabricated and evaluated and results are compared with simulation and predicted data. Based on the recorded data of a real hybrid FSO/RF channel the performance of hybrid FSO/RF link employing the hybrid antenna with a switching mechanism is evaluated. Through this thesis, the detailed guidelines on design of the hybrid antenna are outlined and when necessary, the significant issues are discussed and addressed. Since the propose of this PhD is to outline and demonstrate the proof of concept for the proposed hybrid antenna, therefore the focus has been on the design, evaluation and the minimum performance requirements rather than the best possible performance or optimising the communication link quality. The outcome of the thesis will be a prototype antenna with a gain of 29.2 dBi and efficiency of 59 % at the frequency of 10 GHz for use in a hybrid FSO/RF system. It will be shown that the designed antenna is able to provide a hybrid link with 99.8 % availability and 1 Gbits/sec data rate at the recorded fog and rain channel conditions.

In the past few decades, there has been a growing demand for bandwidth in wireless communication systems due to an increase in the number of mobile users, computer network applications and high speed internet access and services. Visible light communication (VLC) is a newly emerging technology in optical wireless communication (OWC) systems to provide both illumination and high-speed data communication. In addition, it can also be used for indoor positioning or localization with wide applications that has merited a number of attractive research studies. However, security in wireless communications has become a matter of concern due to the possibility of unauthorised access to transmitted data. This thesis investigates received optical power (ROP) distribution to achieve illumination requirements for both optimal and sub-optimal Lambertian order in single and four cell configurations. Furthermore, it proposes VLC-based indoor positioning by using the received optical power levels from the emitting LEDs. Both scenarios of line-of-sight (LOS) and line-of-sight with non-line-of-sight (LOSNLOS) positioning are considered. The performance of the proposed system is evaluated under both noisy and noiseless channel cases and the impact of different location codes on the positioning error is also investigated. An analytical model of the system with noise and the corresponding numerical evaluation for a range of signal to noise ratios (SNRs) are presented. The results show that an accuracy of 8 cm in average is achievable at an SNR of 15 dB in the LOSNLOS scenario. We also introduce a novel approach for recovering 4×4 MIMO–VLC data with partial channel state information (CSI) knowledge both in noisy and noiseless cases. In addition, the proposed indoor localization system utilizing two visible light emitting diodes for different environments offering less complexity for both LOS and LOSNLOS scenarios is offered. The results of the scheme is compared with existing trilateration techniques and the performance of the proposed system is evaluated with a reported accuracy of less than 20 cm for SNR values of greater than 13 dB. This thesis also proposes a new secure single input single output (SISO) VLC system and investigates the bit error rate (BER) performance with and without encryption in the Media Access Control (MAC) layer and physical layer for both the LOS and LOSNLOS scenarios. For a BER of 10-3, the results show that there is 1 to ~ 3.5 dB power penalties for the secured VLC system for data rates of up to 10 Mbps. The key length impact on the error propagation is also investigated. Finally, this thesis proposes a secure MIMO VLC system that relies on the position of the user by incorporating a new modified version of the Rivest-Shamir-Adleman (RSA) technique for encrypting the transmitted data in the MAC layer. Furthermore, the ability of the proposed system to control the size of the encrypted cell depending on the application environment is demonstrated.

Brillouin based distributed fibre sensors gained a lot of attention in recent years for structural health monitoring applications, due to their higher sensing range over tens of kilometres and distributed measurement capability of simultaneous strain and temperature. In Brillouin optical time domain reflectometry (BOTDR) system, the signal-to-noise ratio (SNR) determines the sensing performance of the system. However, the SNR is limited by the restricted maximum input pump power, which is limited by the non-negligible nonlinear effects, such as stimulated Brillouin scattering. In this research, a novel wavelength diversity technique is proposed to enhance the SNR, hence improve the strain and temperature measurement accuracies, which is required for accurate rail-track condition monitoring. In addition, this research work presents the following contributions (i) a simple, low-cost passive depolarizer is adopted to reduce the polarization noise; (ii) an inline erbium-doped fibre amplifier (EDFA) is employed at a certain distance to amplify the attenuated pulse in order to improve the sensing range; and (iii) a cost-effective reference Brillouin ring laser is used in BOTDR system to overcome the complexity of the receiver bandwidth reduction. The proposed wavelength diversity BOTDR system combined with a passive depolarizer and Brillouin ring laser is validated over a 50 km sensing fibre with a 5 m spatial resolution. The SNR is improved by 5.1 dB, which corresponds to 180% improvement compared to a conventional BOTDR system. Whereas, the strain and temperature accuracies at a 50 km fibre distance are ±10 με and ±0.45oC, respectively. Furthermore, for the first time, simultaneous integration of long-term evolution (LTE) radio-over-fibre (RoF) data system and BOTDR sensing system using a single optical fibre is proposed and demonstrated. The error vector magnitude (EVM) performance of LTE-RoF data system is analysed for three modulation formats of QPSK, 16-QAM and 64-QAM in the presence of various BOTDR sensing powers.

In this day and age, free space optical (FSO) enable the deployment of a new category of products that can transmit voice, data, and video at bandwidths up to 2.5 Gbps at distances up to 4 km, over any protocol. This optical connectivity doesn’t require expensive fibre-optic cable or spectrum licenses. FSO is reliable due to the capability of FSO systems to provide truly broadband and secure communications, as well as their immunity to interference from other sources of optical radiation. The principal challenge facing FSO technology is to achieve 100% link availability in all weather conditions. While rain, fog, haze, turbulence and aerosols all attenuate the optical signal to a certain level, fog is considered to be the main impairment in FSO systems. Thick fog resulting in over 300 dB/km of signal attenuation can reduce the transmission span from a few kilometres to just 100 m or so. Turbulence (i.e. scintillation) also results in reducing fade margins from 4 to 10 dB for FSO links of 1 km length or less, which is well below the margins for atmospheric attenuation. In the real-world environment, it is very challenging to measure the effect of atmospheric fog under diverse circumstances. This is due to several reasons: (i) the longer observation time required and the lower probability of reoccurrence of dense fog events for visibility V < 0.5 km, and (ii) the difficulty in controlling and characterising aerosols in the atmosphere, due to the inhomogeneous presence of aerosols along the FSO link path. This thesis examines and analyses the performance of a terrestrial FSO system by investigating the impact of a number of modulation techniques on mitigating the atmospheric impairments. A dedicated indoor atmospheric chamber is designed to carry out tests and measurements in a controlled manner and mimic the real outdoor atmosphere. The experimental results are compared with predicted data for the range of modulation techniques tested in the presence of atmospheric turbulence and fog, including binary phase shift keying subcarrier intensity modulation (BPSK-SIM), 2-pulse position modulation (2-PPM), 4-pulse position modulation (4-PPM) and hybrid pulse position modulation binary phase shift keying subcarrier intensity modulation (BPSK-SIM-PPM).The results show that BPSK-SIM-PPM offers a similar performance to 2-PPM, a superior performance to BPSK-SIM, while having the same bandwidth, and an inferior performance to 4-PPM under turbulent conditions. Furthermore, the experimental investigation indicates that 4-PPM is more resistant to turbulence compared to BPSK-SIM. The improvement of the link performance by optimising the beam spot size using combinations of mirrors is also investigated. In addition, the effects of low to high visibility on the FSO link BER performance in the presence of fog are measured and investigated. The obtained results indicate the dependency of the performance of the FSO link on the fog intensity variation. Moreover, the experimental results show that the impact of severe fog induced attenuation is greater on the receiver than the transmitter. Finally, the effect of fog on an FSO system employing quadrature phase-shift keying (QPSK) and operating at various carrier wavelengths is also studied.

Communications infrastructure plays an important role in industrial monitoring, automation and process control. Recently, wireless solutions have emerged to offer communications in industrial processes to establish feedback control. Due to cost efficiency, localized processing, application specific and resource efficient design, flexibility, and self-healing abilities, Industrial Wireless Sensor Networks (IWSNs) emerge as the most promising technology for industrial automation. Despite the seamless advantages, IWSNs still suffer from the reliability and real-time data delivery issues inherent in the wireless networks. These issues are more prominent in the emergency communications, regulatory feedback control systems and supervisory feedback control systems. The research focuses on communications and system feedback related problems of IWSNs in applications in automation and process control industry including, emergency systems, regulatory control systems, supervisory control systems open loop control systems, alerting systems and monitoring systems. The research targets communication assurances, reliability improvement, real-time sensory data propagation and energy efficiency in IWSNs. It also targets the traffic scheduling from heterogeneous sensing nodes to improve the overall network efficiency, reliable data scheduling and deterministic schedule formation for coexisting industrial systems. The notable contributions of the research cover following aspects of IWSNs • A novel scheme is proposed to ensure instant channel access for emergency communications. The scheme integrates emergency communications within the regular communications channel without compromising the reliability and time sensitivity of the information. Thus, improving network flexibility along with improved reliability and real-time data delivery. The improvements proposed in the emergency communications are further extended to the regulatory control and supervisory control applications where superframe of variable durations are introduced to offer higher reliability within the communication feedback links. • Dynamic priority system is proposed which takes in to consideration the critical parameters in industrial processes to offer suitable urgency index to the sensory data based on real-time analysis of parameters. Using the priority system, MAC layer optimizations are proposed to 1) improve the reliability of high priority nodes’ communications, 2) ensure pre-specified Packet Reception Rate (PRR) within the network. • An efficient update mechanism is proposed to offer improved energy efficiency and network reliability in gradient-based routing protocols. Two schemes: periodic setup and multiple setup, are proposed along with secondary update mechanisms to keeps the routing path updated with minimal control overhead. Furthermore, an optimizable gradient cost function is also proposed. • A low complexity, scheduling algorithm is proposed, which allows multiple classes of industrial systems to coexist and share same wireless resource and to distinctly schedule information from diverse industrial processes with heterogeneous time deadlines.

Visible light communications (VLC) is an emerging technology of optical wireless communications, which has been in the research spotlight recently, thanks to the remarkable development of light emitting diodes. Furthermore, optical camera communications, a timely VLC topic, has earned a great share of researchers'interest in the last few years, given the wide availability of digital cameras. This thesis proposes to merge two separate technologies: image processing and VLC, to create a camera-based VLC system. Moreover, the work presented in this thesis describes a short-range mobile-to-mobile communication link, where the transmitter and the receiver are the smartphone’s screen and camera, respectively. In addition, the data is encoded into images and subsequently beamed out of the transmitter's screen, and the receiver's camera captures consecutive frames containing the transmitter's screen to extract the data. The proposed system offers inherent advantages in terms of portability and simplicity of implementation as it uses available screens and smartphone cameras. Additionally, the system is software-based and does not require any hardware modifications on the devices, thus making a high potential for millions of consumers. The system proposed in this thesis is designed for mobile users. Therefore, high performance in dynamic environments is required. Moreover, combining image processing and VLC for smartphone to smartphone VLC is an innovative topic and very few works reported similar communication links. As such, it is imperative to investigate the impact of computer vision challenges on the system's performance, such as the detection of the transmitter by the receiver's camera, in dynamic conditions. Consequently, this work focuses on the development of an effective algorithm to capture frames containing the transmitter as well as other objects in the background, detect the transmitter contained in the received frames, and then finally extract the originally transmitted information. The end-to-end system is fully implemented on a mobile platform and a range of experiments are carried out in order to evaluate the system's performance. It is proved that the system is able to achieve very high success rate that reaches 98% data recovery of transmitted images under test conditions, demonstrating a practical link with a possible 100 kbps data transmission capability.