Multiple-antenna systems offer significant performance enhancement and will be applied to the next generation broadband wireless communications. This thesis presents the investigations of multiple-antenna systems – multiple-input multiple-output (MIMO) and cooperative communication (CC) – and their performances in more realistic propagation environments than those reported previously. For MIMO systems, the investigations are conducted via theoretical modelling and simulations in a double-scattering environment. The results show that the variations of system performances depend on how scatterer density varies in flat fading channels, and that in frequency-selective fading channels system performances are affected by the length of the coding block as well as scatterer density. In realistic propagation environments, the fading correlation also has an impact on CC systems where the antennas can be further apart than those in MIMO systems. A general stochastic model is applied to studying the effects of fading correlation on the performances of CC systems. This model reflects the asymmetry fact of the wireless channels in a CC system. The results demonstrate the varied effects of fading correlation under different protocols and channel conditions. Performances of CC systems are further studied at the packet level, using both simulations and an experimental testbed. The results obtained have verified various performance trade-offs of the cooperative relaying network (CRN) investigated in different propagation environments. The results suggest that a proper selection of the relaying algorithms and other techniques can meet the requirements of quality of service for different applications.

No description available.

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.

Computational Grids are evolving into a global, service-oriented architecture – a universal platform for delivering future computational services to a range of applications of varying complexity and resource requirements. The thesis focuses on developing a new scheduling model for general-purpose, utility clusters based on the concept of user requested job completion deadlines. In such a system, a user would be able to request each job to finish by a certain deadline, and possibly to a certain monetary cost. Implementing deadline scheduling is dependent on the ability to predict the execution time of each queued job, and on an adaptive scheduling algorithm able to use those predictions to maximise deadline adherence. The thesis proposes novel solutions to these two problems and documents their implementation in a largely autonomous and self-managing way. The starting point of the work is an extensive analysis of a representative Grid workload revealing consistent workflow patterns, usage cycles and correlations between the execution times of jobs and its properties commonly collected by the Grid middleware for accounting purposes. An automated approach is proposed to identify these dependencies and use them to partition the highly variable workload into subsets of more consistent and predictable behaviour. A range of time-series forecasting models, applied in this context for the first time, were used to model the job execution times as a function of their historical behaviour and associated properties. Based on the resulting predictions of job runtimes a novel scheduling algorithm is able to estimate the latest job start time necessary to meet the requested deadline and sort the queue accordingly to minimise the amount of deadline overrun. The testing of the proposed approach was done using the actual job trace collected from a production Grid facility. The best performing execution time predictor (the auto-regressive moving average method) coupled to workload partitioning based on three simultaneous job properties returned the median absolute percentage error centroid of only 4.75%. This level of prediction accuracy enabled the proposed deadline scheduling method to reduce the average deadline overrun time ten-fold compared to the benchmark batch scheduler. Overall, the thesis demonstrates that deadline scheduling of computational jobs on the Grid is achievable using statistical forecasting of job execution times based on historical information. The proposed approach is easily implementable, substantially self-managing and better matched to the human workflow making it well suited for implementation in the utility Grids of the future.

All-optical packet switched networks with flexibility and capability to deal with the bursty traffic is one solution to deal with the ever increasing demand for bandwidth. To fully utilise the potential of such networks and to ensure that high-speed packets, passed through a number of nodes, are faithfully delivered to their intended destination with minimum delay times, packet header processing and routing decision needs to be carried out in the optical domain not in the electrical domain. This is to avoid the speed bottleneck imposed by the slow response of currently available electronic devices beyond 40 Gb/s. At present, packet header recognition is carried out by sequentially correlating the incoming packet header address with every entry of a local routing table. For a small size network, with a reasonable size routing table, sequential correlation is viable both in terms of processing speed and implementation complexity. However, for a large size network with a very large size routing table of hundreds or thousands of entries, the cost, complexity and processing time does become a real issue. The latter will lead to a noticeable increase in the packet processing time at every router, which could be significantly reduced by a non- conventional signal formatting. In this thesis, an all-optical 3-input AND gate and an all-optical 1 x2 switch with high contrast ratio are proposed as an essential element in all-optical routers. New routing schemes employing pulse position modulation (PPM) packet header format as well as single and multiple PPM based routing tables (PPRTs) are proposed and investigated. The main advantage of the proposed scheme is reduced size routing table leading to a faster router processing time compared to the routers with conventional routing tables (CRTs). The correlation-time gains offered by the proposed schemes are given by theoretical calculations. For optical packets with 4-bit binary address, all-optical 1x3 routers employing single and multiple PPRTs with an entry slot of 6.25 ps offer — 100 and — 400 times faster processing times when compared to the routers employing CRT, respectively. The performance of the proposed routers employing single and multiple PPRTs are assessed in terms of optical signal-to-noise ratio (OSNR) in multi-hop routing by means of numerical simulations and theoretical analysis. It is shown that predicted and simulated OSNR decreases by —2 dB after each hop. New packet header address formats proposed offers reduced complexity of nodes by employing single or multiple PPM based routing tables. Adopting a hybrid header address format, it is shown that routers with multiple PPRTs can operate at 160 Gb/s with the output intra-channel crosstalk of -18 dB and with output packet power fluctuation of 2 dB. Finally, a WDM router employing a single PPRT, capable of processing packets at different wavelengths simultaneously, is proposed and its inter-channel crosstalk performance is investigated. At 160 Gb/s, results obtained show an inter-channel crosstalk of — -27 dB at a channel spacing of greater than 0.4 THz and a demultiplexer bandwidth of 500 GHz.

This thesis investigates the use of Wavelet Analysis and Artificial Intelligence as elements of a diffuse indoor infrared (IR) optical wireless communications receiver. The work presented employs MatlabTM enabled simulations to explore the effects of inter symbol interference (ISI) and fluorescent light interference on a receiver using these techniques. The results are compared with those obtained from traditional receiver architectures. IR devices have been commonplace in most households as remote control handsets for domestic entertainment equipment for many years. More recently, IR communication systems have been deployed in mobile phones, laptop computers and computer peripheral devices largely for the purpose of short range point-to-point data transfers. Since the late 1970's there has been consistent interest and research in the use of the IR part of the spectrum for short-range Wireless Local Area Networks (WLAN). IR offers a number of potential advantages over radio frequency systems such as unregulated and re-usable bandwidth, inherent security, resistance to multipath fading and the availability of mass produced, low cost emitters and detectors. However, significant problems still persist to impede the widespread and popular deployment of IR enabled LANs. The work presented in this thesis focuses on the use of the largely software enabled techniques of Wavelet Analysis and Artificial Intelligence (Wavelet-AI) as novel alternatives to mitigating the difficulties associated with diffuse indoor IR communication systems. Indoor IR wireless links usually have to operate in the presence of intense noise generated by ambient light sources. The source can be natural sunlight from doors and windows, or artificial light from incandescent and fluorescent fittings. In addition to contributing to the generation of shot noise, artificial light sources can also impose a periodic interference signal that can significantly impair the performance of an optical link. Electrical high pass filtering is a typical mitigating technique that is effective at reducing the interference signal. Unfortunately it also introduces a performance degrading phenomenon known as baseline wander. Using well established interferer models the results of original Wavelet-AI inclusive simulations are presented and compared with those of typical receiver architectures with and without electrical high pass filtering. The performance of Wavelet-AI based receiver was found to be superior to traditional unfiltered receiver architecture in the presence of artificial light interference. At low to medium data rates the Wavelet-AI receiver was also found to outperform all but one case of the traditional receiver architecture employing electrical high pass filtering. The results of baseline wander simulations with On-and-Off keying (00K) modulation and the Wavelet-Al receiver architectures is presented and shows that the Wavelet-AI architecture is far more tolerant to baseline wander. In diffuse or non-directed links multipath propagation induced ISI can impose a significant performance penalty for data rates above approximately 10 Mb/s. Typical compensation techniques include the use of equalisers such as the zero-forcing equaliser (ZFE), the minimum mean square equaliser (MMSE) and the decision feedback equaliser (DFE), usually implemented as digital filters. The results of original Wavelet-Al inclusive simulations are presented and compared with those of typical receiver architectures with and without filtering and equalisers. In all cases the simulation results show that the Wavelet-Al receiver architecture performance is superior to the non-equalised traditional receiver. The Wavelet-AI receiver results show a very similar performance to the equalised traditional OOK receiver and the equalised Level 4 Pulse Position Modulation (4-PPM) receiver. However, between a 2 dB and 4 dB optical power penalty was incurred for the 8-PPM Wavelet-AI case.

This work describes an investigation into the performance of antennas for mobile base station applications and techniques for improving the coverage and capacity within a base station cell. The work starts by tracing the development of mobile systems, both in technical and commercial terms, from the earliest analogue systems to present day broadband systems and includes anticipated future developments. This is followed by an outline of how smart antenna systems can be utilised to improve cell coverage and capacity. A novel smart antenna system incorporating an array of slant ± 450 dual- polarised stacked patch elements four columns wide excited by a novel multi-beam forming and beam shaping network has been designed, simulated and implemented. It is found that for an ideal smart antenna array, four narrow overlapping beams, one wide “broadcast channel” beam and right and left shaped beams can be provided. Results are presented for the simulation of the smart antenna system using CST EM simulation software which inherently includes mutual coupling and the effects of a truncated ground plane on the element patterns. The results show some significant changes to the desired set of coverage patterns and various mutual coupling compensation techniques have been reviewed. An improved design technique has been developed for compensating the performance degrading effects of mutual coupling and finite ground plane dimensions in microstrip antenna arrays. The improved technique utilises combination of two previously known techniques: complex excitation weights compensation by inversion of the array mutual coupling scattering matrix and the incorporation of a WAIM (wide angle impedance matching) sheet. The technique has been applied to a novel multi-beam smart antenna array to demonstrate the efficacy of the technique by electromagnetic simulation. In addition, a demonstrator array has been constructed and tested which has yielded a positive conformation of the simulation results. For the developed demonstrator array which provides seven different beams, beams “footprints” have been predicted both for free space propagation and for urban propagation to evaluate the dynamic capacity performance of the smart antenna in a 3G mobile network. The results indicate that sector capacity can be dynamically tailored to user demand profiles by selection of the appropriate beam patterns provided by the novel smart antenna system.

Terrestrial free-space optical (FSO) communications is an emerging low-license-free and high-bandwidth access solution, albeit hampered by the combined effects from atmospheric loss, turbulence and pointing errors (PEs). Partially coherent beams (PCBs) are capable of mitigating the turbulence-induced signal fading and PEs, while causing reduction in the mean received signal intensity. This implies the necessity of PCB optimization technique, such that the trade-off between the reduction in the scintillation index and the decrease in the mean received irradiance can be achieved conveniently. This thesis investigates the performance of partially coherent FSO communication links from the information theory perspective. The important link design criteria are considered, and the Gaussian-Schell beam model is adopted to characterize the optical beam propagation through random turbulent medium. Numerical results show that beam width optimization presents a feasible approach in promoting capacity enhancement for long-distance terrestrial FSO systems, since the optimum beam width is susceptible to the deterring effects of atmospheric turbulence and PEs. Next, joint investigation of the effects of a PCB and aperture averaging is presented, which confirms the distinctive advantages of introducing an enlarged receiver aperture and the interest of optimizing the beam width to maximize the FSO channel capacity. A theoretical beam width optimization model is proposed to determine the optimum beam width. Subsequent investigation studies on the characteristics of PCB propagating through the turbulent channel reveal the relationship between the beam width and spatial coherence length to optimize the PCB. Therefore, a joint beam width and spatial coherence length optimization technique is proposed to maximize the average capacity in partially coherent FSO links. An optimization metric is developed to enable a feasible translation of the joint optimal transmitter beam parameters into an analogous level of divergence of the received optical beam. It is demonstrated that the PCBs are desirable in the weak-to-moderate turbulence regimes, whereas coherent laser beams with high transmit power exhibit greater resilience to strong turbulences. An experimental study is carried out to demonstrate the effects of aperture averaging and beam width on the FSO link under laboratory-controlled atmospheric turbulence conditions. The aperture-averaging effect is characterized through the signal density distributions, showing good agreement with the theoretical models. It is demonstrated that the relationship between the aperture averaging factor and point-received scintillation index can be described by a first-order linear regression model, whereby the coefficients of the model are provided and compared. Measurements of the Q-factor for an apertureaveraged optical receiver and its corresponding finite point receiver reveals that manifold gain in the link performance can be achieved with increasing scaled aperture size, thus concluding that the introduction of an enlarged receiver aperture enhances the effective collection of the optical signal and potentially mitigates the scintillation effect. Atmospheric loss resulting from visibility-limiting weather conditions significantly attenuates the intensity of a propagating laser beam, which imposes degrading impacts on the link range and availability. Hybrid FSO and radio frequency (RF) systems present the most prominent alternative to enable these technologies in complementing one another’s weaknesses, since fog and rain drastically affect the FSO and RF links, respectively, but only insignificantly vice versa. The viability of deploying the media diversity technique in the FSO system is investigated through a case study, in which a new hybrid-base transceiver station (H-BTS) system architecture is proposed for the green Metrozones. The hybrid FSO/RF system is integrated at the macro-cellular tier, to enable high-capacity, power-efficient wireless backhauling. A resource prioritization mechanism is designed, to maintain good control and optimal on-demand resource allocation, and to establish sustainable backhaul link availability. Next, a basic access signalling (BAS) scheme is introduced, to necessitate the discovery, registration and monitoring of active metro access points (M-APs). The proposed BAS scheme enables the sleep-wake-on-demand (SWoD) mechanism and the cooperative inter-cell support. Findings from this work suggest that adaptation and optimization at the link- and system-level are vital for Metrozones deployment, due to the occurrence of numerous time-varying factors in real networks.

The primary goal of this research is to investigate the existing photovoltaic antenna integration techniques and develop a new solar antenna integration topology in order to address the drawbacks of these techniques. With the increasing demands for low-profile antennas and a growing move towards the microgeneration of electricity, primarily by photovoltaics, photovoltaic antennas are of increasing importance with a growing amount of research in this area being developed. At present there are a number of designs for photovoltaic antennas which could be divided into two distinct categories. The first type is the use of solar cells as an RF ground plane, whilst the second type involves the use of solar cells as an RF radiating element. Both techniques bring significant challenges if they are to be widely adopted. Considering the first technique, using a solar cell as an RF ground plane introduces an optical shading problem, which significantly reduces the solar efficiency of the solar antennas using this integration topology. To this end, meshing the RF radiating element is investigated in this thesis to achieve optical transparency at the expense of increasing the cost and complexity of the fabrication process of photovoltaic antennas. Conversely, using a solar cell as an RF radiating element limits the ability to modify the resonance response using traditional RF bandwidth enhancement techniques due to the fact that solar cells need to have a homogeneous structure to achieve optimum solar performance. In order to address these challenges, a third solar antenna integration topology is proposed in this thesis. This method is based upon the use of solar cells as an RF stacked parasitic patch element suspended above the conventional RF radiating element of the integrated antennas. This integration topology enables the integrated solar cells to achieve an optimum solar efficiency due to their suspended position eliminating the shading problem. It also enables the RF radiating element to be modified to excite multiple TMmn propagation modes to achieve enhanced resonance response for multiband and wideband applications. This new topology has been further developed and applied to design a dual-polarised photovoltaic antenna for polarisation diverse communication systems, which has been extended to produce a photovoltaic array antenna for beam steering applications. This thesis addresses a major knowledge gap in the field of photovoltaic antennas. As a result of this, greater understanding of the design procedures of photovoltaic antennas and associated trade-offs from such designs is developed. Using this knowledge, novel designs that overcome the associated problems of current photovoltaic antennas are presented.

Due to substantial generation and demand fluctuations in stand-alone green micro-grids, energy management strategies (EMSs) are becoming essential for the power sharing purpose and regulating the microgrids voltage. The classical EMSs track the maximum power points (MPPs) of wind and PV branches independently and rely on batteries, as slack terminals, to absorb any possible excess energy. However, in order to protect batteries from being overcharged by realizing the constant current-constant voltage (IU) charging regime as well as to consider the wind turbine operational constraints, more flexible multivariable and non-linear strategies, equipped with a power curtailment feature, are necessary to control microgrids. This dissertation work comprises developing an EMS that dynamically optimises the operation of stand-alone dc microgrids, consisting of wind, photovoltaic (PV), and battery branches, and coordinately manage all energy flows in order to achieve four control objectives: i) regulating dc bus voltage level of microgrids; ii) proportional power sharing between generators as a local droop control realization; iii) charging batteries as close to IU regime as possible; and iv) tracking MPPs of wind and PV branches during their normal operations. Non-linear model predictive control (NMPC) strategies are inherently multivariable and handle constraints and delays. In this thesis, the above mentioned EMS is developed as a NMPC strategy to extract the optimal control signals, which are duty cycles of three DC-DC converters and pitch angle of a wind turbine. Due to bimodal operation and discontinuous differential states of batteries, microgrids belong to the class of hybrid dynamical systems of non-Filippov type. This dissertation work involves a mathematical approximation of stand-alone dc microgrids as complementarity systems (CSs) of Filippov type. The proposed model is used to develop NMPC strategies and to simulate microgrids using Modelica. As part of the modelling efforts, this dissertation work also proposes a novel algorithm to identify an accurate equivalent electrical circuit of PV modules using both standard test condition (STC) and nominal operating cell temperature (NOCT) information provided by manufacturers. Moreover, two separate stochastic models are presented for hourly wind speed and solar irradiance levels.