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Rapidly growing internet traffic volume is the major driving force behind the development of optically-transparent and ultrahigh-capacity photonic packet-switching networks. In such networks, the packet routing decision at each router is made by sequentially correlating an incoming packet header address with addresses in all entries of the router's look-up routing table. The routing task is achieved in the optical domain using all-optical logic gates and optical correlator technologies which have been predominantly replacing the existing low-speed electronic processing devices. Nevertheless when a network is expanded, a larger routing table is required thus exponentially increasing header processing time, which results in the increases in routing latency and complexity. This research aims to significantly reduce the size of the routing table and the number of optical devices required in a router by mapping both the packet header address and the look-up routing table entries into the pulse-position-modulation format, where more than one address could be located in a single entry of a new pulse-position routing table. By simply carrying out a single correlation of the packet header address with pulse- position routing table entries, the router can instantly obtain the routing decision, thus significantly reducing the processing time and neglecting the gain recovery time in existing optical logic gates. The structure of the pulse-position routing table also offers flexibility in the transmission mode including unicast, multicast or broadcast embedded in the optical (physical) layer. In the thesis, a new router based on the pulse-position¬modulation scheme will be introduced. Essential router modules including high on-off contrast-ratio clock extraction, pulse position routing table, header processing and optical switch are proposed and analysed. In addition, the thesis investigates and improves the switching window profile and residual crosstalk performance of the all- optical Mach-Zelmder switches as a building block for the implementation of the above router modules. A number of new variants of Mach-Zehnder-based switches are also introduced to enhance switching inter-output contrast ratio and reduce the complexity in multiple-channel OTDM demultiplexing.

Indoor location-based services have played a crucial role in the development of various Internet of Things applications over the last few decades. The use of radio frequency (RF)-based systems in indoor environments suffers from additional interference due to the high penetration rate and reflections of the RF, which may severely affect positioning accuracy. Alternatively, the optical technology using the existing light-emitting diode (LED)-based lights, photodetectors (PDs), and/or image sensors could be utilised to provide indoor positioning with high accuracy. Because of its resilience to electromagnetic interference, license-free operation, large bandwidth, and dual-use for illumination and communication, visible light positioning (VLP) systems have shown great potential in achieving high-precision indoor positioning. This thesis focus is on investigating VLP systems based on employing a single PD, or an array of PDs in the form of a single image sensor (i.e. a camera) for both localization and data communication. Following a comprehensive literature review on VLP, the key challenges in existing positioning methods for achieving a low-cost, accurate, and less complex indoor positioning systems design are highlighted by considering the design characteristics of an indoor environment, position accuracy, number of light-emitting LED, PD, and any additional sensors utilized. The thesis focuses on the major constraints of VLP and provides novel contributions. In most reported VLP schemes, the assumptions of fixed transmitter (Tx) angle and height may not be valid in many physical environments. In this work, the impact of tilting Tx and multipath reflections are investigated. The findings demonstrated that tilting Tx can be beneficial in VLP by leveraging the influence of reflections from both near- and far-walls. It also showed that proposed system offers a significant accuracy improvement by up to ~66% compared with a typical non-tilted Tx VLP system. Furthermore, increasing robustness of image sensor-based receiver (Rx) is a major challenge, which is being addressed using a novel angle of arrival-received signal intensity and a single LED. Experimental results show that the proposed algorithm can achieve a three-dimensional root mean squared error of 7.56 cm. Visible light communications employing a camera-based Rx is best known as optical camera communications (OCC), which can also be used for VLP. However, in OCC the transmission data rate is mainly limited by the exposure time and the frame rate of the camera. In addition, the camera's sampling introduces intersymbol interference Indoor location-based services have played a crucial role in the development of various Internet of Things applications over the last few decades. The use of radio frequency (RF)-based systems in indoor environments suffers from additional interference due to the high penetration rate and reflections of the RF, which may severely affect positioning accuracy. Alternatively, the optical technology using the existing light-emitting diode (LED)-based lights, photodetectors (PDs), and/or image sensors could be utilised to provide indoor positioning with high accuracy. Because of its resilience to electromagnetic interference, license-free operation, large bandwidth, and dual-use for illumination and communication, visible light positioning (VLP) systems have shown great potential in achieving high-precision indoor positioning. This thesis focus is on investigating VLP systems based on employing a single PD, or an array of PDs in the form of a single image sensor (i.e. a camera) for both localization and data communication. Following a comprehensive literature review on VLP, the key challenges in existing positioning methods for achieving a low-cost, accurate, and less complex indoor positioning systems design are highlighted by considering the design characteristics of an indoor environment, position accuracy, number of light-emitting LED, PD, and any additional sensors utilized. The thesis focuses on the major constraints of VLP and provides novel contributions. In most reported VLP schemes, the assumptions of fixed transmitter (Tx) angle and height may not be valid in many physical environments. In this work, the impact of tilting Tx and multipath reflections are investigated. The findings demonstrated that tilting Tx can be beneficial in VLP by leveraging the influence of reflections from both near- and far-walls. It also showed that proposed system offers a significant accuracy improvement by up to ~66% compared with a typical non-tilted Tx VLP system. Furthermore, increasing robustness of image sensor-based receiver (Rx) is a major challenge, which is being addressed using a novel angle of arrival-received signal intensity and a single LED. Experimental results show that the proposed algorithm can achieve a three-dimensional root mean squared error of 7.56 cm. Visible light communications employing a camera-based Rx is best known as optical camera communications (OCC), which can also be used for VLP. However, in OCC the transmission data rate is mainly limited by the exposure time and the frame rate of the camera. In addition, the camera's sampling introduces intersymbol interference.

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.

Free space optical (FSO) communication uses visible or infrared (IR) wavelengths to broadcast high-speed data wirelessly through the atmospheric channel. The performance of FSO communications is mainly dependent on the unpredictable atmospheric channel such as fog, smoke and temperature dependent turbulence. However, as the real outdoor atmosphere (ROA) is time varying and heterogeneous in nature as well as depending on the magnitude and intensity of different weather conditions, carrying out a proper link assessment under specific weather conditions becomes a challenging task. Investigation and modelling the ROA under diverse atmospheric conditions is still a great challenge in FSO communications. Hence a dedicated indoor atmospheric chamber is designed and built to produce controlled atmosphere as necessary to mimic the ROA as closely as possible. The experimental results indicate that the fog attenuation is wavelength dependent for all visibility V ranges, which contradicts the Kim model for V < 0.5 km. The obtained result validates that Kim model needs to be revised for V < 0.5 km in order to correctly predict the wavelength dependent fog attenuation. Also, there are no experimental data and empirical model available for FSO links in diverse smoke conditions, which are common in urban areas. Therefore, a new empirical model is proposed to evaluate the wavelength dependent fog and smoke attenuation by reconsidering the q value as a function of wavelength rather than visibility. The BER performance of an FSO system is theoretically and experimentally evaluated for OOK- NRZ, OOK-RZ and 4-PPM formats for Ethernet line data-rates from light to dense fog conditions. A BER of 10-6 (Q-factor ≈ 4.7) is achieved at dense fog (transmittance, T = 0.33) condition using 4-PPM than OOK-NRZ and OOK-RZ modulation schemes due to its high peak-to-average power ratio albeit at the expense of doubling the bandwidth. The effects of fog on OOK-NRZ, 4-PAM and BPSK are also experimentally investigated. In comparison to 4-PAM and OOK-NRZ signals, the BPSK modulation signalling format is more robust against the effects of fog. Moreover, the effects of using different average transmitted optical communication powers Popton the T and the received Q-factor using the OOK-NRZ modulation scheme are also investigated for light and dense fog conditions. The results show that for an FSO system operating at a Q-factor of 4.7 (for BER = 10-6), the required Q-factor is achieved at T of 48% under the thick fog condition by increasing Popt to 1.07 dBm, whereas the values of T are 55% and ~70% for the transmit power of 0.56 dBm and -0.7 dBm, respectively. The experimental characterisation and investigation of the atmospheric turbulence effect on the Ethernet and Fast-Ethernet FSO link is reported using different modulation schemes. The experiment is carried out in a controlled laboratory environment where turbulence is generated in a dedicated indoor atmospheric chamber. The atmospheric chamber is calibrated to mimic an outdoor turbulence conditions and the measured data are verified against the theoretical predictions. The experiment also demonstrates methods to control the turbulence levels and determine the equivalence between the indoor and outdoor FSO links. The results show that the connectivity of Ethernet and Fast-Ethernet links are highly sensitive to atmospheric turbulence. The results also show that the BPSK and OOK-NRZ modulation signalling formats are more robust against the weak atmospheric turbulence conditions than PAM signal.