45 research outputs found
Physical Layer Techniques for High Frequency Wireline Broadband Systems
This thesis collects contributions to wireline and wireless communication systems with an emphasis on multiuser and multicarrier physical layer technology. To deliver increased capacity, modern wireline access systems such as G.fast extend the signal bandwidth up from tens to hundreds of MHz. This ambitious development revealed a number of unforeseen hurdles such as the impact of impedance changes in various forms. Impedance changes have a strong effect on the performance of multi-user crosstalk mitigation techniques such as vectoring. The first part of the thesis presents papers covering the identification of one of these problems, a model describing why it occurs and a method to mitigate its effects, improving line stability for G.fast systems.A second part of the thesis deals with the effects of temperature changes on wireline channels. When a vectored (MIMO) wireline system is initialized, channel estimates need to be obtained. This thesis presents contributions on the feasibility of re-using channel coefficients to speed up the vectoring startup procedures, even after the correct coefficients have changed, e.g., due to temperature changes. We also present extensive measurement results showing the effects of temperature changes on copper channels using a temperature chamber and British cables. The last part of the thesis presents three papers on the convergence of physical layer technologies, more specifically the deployment of OFDM-based radio systems using twisted pairs in different ways. In one proposed scenario, the idea of using the access copper lines to deploy small cells inside users' homes is explored. The feasibility of the concept, the design of radio-heads and a practical scheme for crosstalk mitigation are presented in three contributions
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The Design of Resilient Engineering Infrastructure Systems
The concept of resilience has emerged from a number of domains to address how systems, people as well as organisations can handle uncertainty and thereby not only survive hardship, but also thrive and prosper. This is of particular importance for engineering infrastructure systems which, due to the inherently long lifecycles giving rise to many unknowns, need to be designed for resilience such that it not only maintains operations in the face of day-to-day demands, but also continue to be able to evolve for the future. While there has been substantial interest in resilience from both academia and industry, exactly how such systems may be endowed with resilience to address these concerns from an engineering design perspective is less clear.
To this end, a literature review was first conducted to compile the definitions and characteristics of resilience across the domains of engineering, organisational management and ecology. The characteristics were found to comprise: absorbing disturbances, adapting for change and thriving for the future. These were then mapped to the engineering design ilities of robustness, adaptability and flexibility before being brought together in a conceptual model to form a strategic view for resilience. Further methods from resilience and engineering design literature were then consulted to understand how this particular view could be modelled and evaluated. This led to the development of a preliminary model using the Least Squares Monte Carlo method adapted for a telecommunications case study.
The insights gained from these explorations were then used to drive the synthesis of a novel support method whereby the design for flexibility framework was adapted to include decision modelling with Bayesian Networks and for resilience analysis. Here, resilience is taken to be the maximisation of the system economic lifecycle value under uncertainty, as measured by Expected Net Present Value, through robust and flexible strategies. This was applied to two case studies involving infrastructure systems: the first built upon existing work based on a Waste-to-Energy system in Singapore to verify the new method while the second applied the support method with BT, a multinational telecommunications company based in the UK, to gauge reception of this approach in industry. In both cases, the initial capacity and maximum number of upgrades served as proxies for robustness and flexibility respectively. Results demonstrate that Bayesian Networks are able to model decision rules for flexibility by selecting technology options over time given observations on the system and are also useful for extracting expert domain knowledge. While the construction of Bayesian Networks are subjective, they present an intuitive visualisation of the dependencies in a system and as such, engaged stakeholder interest. Resilience analysis examined the effect of volatility and drift of demand on the design strategies and indeed, there existed a trade-off between robust and flexible strategies. Furthermore, the greater utility of the support method lies in aiding decision makers in exploring the solution space and prompting discussions for what-if scenarios for the organisation.BT Grou
Intersymbol and Intercarrier Interference in OFDM Transmissions through Highly Dispersive Channels
This work quantifies, for the first time, intersymbol and intercarrier
interferences induced by very dispersive channels in OFDM systems. The
resulting achievable data rate for \wam{suboptimal} OFDM transmissions is
derived based on the computation of signal-to-interference-plus-noise ratio for
arbitrary length finite duration channel impulse responses. Simulation results
point to significant differences between data rates obtained via conventional
formulations, for which interferences are supposed to be limited to two or
three blocks, versus the data rates considering the actual channel dispersion
Mitigation of impulsive noise for SISO and MIMO G.fast system
To address the demand for high bandwidth data transmission over telephone transmission lines, International Telecommunication Union (ITU)
has recently completed the fourth generation broadband (4GBB) copper
access network technology, known as G.fast.
Throughout this thesis, extensively investigates the wired broadband
G.fast coding system and the novel impulsive noise reduction technique
has been proposed to improve the performance of wired communications
network in three different scenarios: single-line Discrete Multiple Tone
(DMT)- G.fast system; a multiple input multiple-output (MIMO) DMTG.fast system, and MIMO G.fast system with different crosstalk cancellation methods. For each of these scenarios, however, Impulsive Noise
(IN) is considered as the main limiting factor of performance system.
In order to improve the performance of such systems, which use higher
order QAM constellation such as G.fast system, this thesis examines the
performance of DMT G.fast system over copper channel for six different
higher signal constellations of M = 32, 128, 512, 2048, 8192 and 32768 in
presence of IN modelled as the Middleton Class A (MCA) noise source.
In contrast to existing work, this thesis presents and derives a novel
equation of Optimal Threshold (OT) to improve the IN frequency domain mitigation methods applied to the G.fast standard over copper
channel with higher QAM signal constellations. The second scenario,
Multi-Line Copper Wire (MLCW) G.fast is adopted utilizing the proposed MLCW Chen model and is compared to a single line G-fast system
by a comparative analysis in terms of Bit-Error-Rate(BER) performance
of implementation of MLCW-DMT G.fast system. The third scenario,
linear and non-linear crosstalk crosstalk interference cancellation methods are applied to MLCW G.fas and compared by a comparative analysis
in terms of BER performance and the complexity of implementation.University of
Technology for choosing me for their PhD scholarship and The Higher
Committee For Education Development in Iraq(HCED
Multi-Hop Wireless Optical Backhauling for LiFi Attocell Networks: Bandwidth Scheduling and Power Control
The backhaul of hundreds of light fidelity (LiFi) base stations (BSs)
constitutes a major challenge. Indoor wireless optical backhauling is a novel
approach whereby the interconnections between adjacent LiFi BSs are provided by
way of directed line-of-sight (LOS) wireless infrared (IR) links. Building on
the aforesaid approach, this paper presents the top-down design of a multi-hop
wireless backhaul configuration for multi-tier optical attocell networks by
proposing the novel idea of super cells. Such cells incorporate multiple
clusters of attocells that are connected to the core network via a single
gateway based on multi-hop decode-and-forward (DF) relaying. Consequently, new
challenges arise for managing the bandwidth and power resources of the
bottleneck backhaul. By putting forward user-based bandwidth scheduling (UBS)
and cell-based bandwidth scheduling (CBS) policies, the system-level modeling
and analysis of the end-to-end multi-user sum rate is elaborated. In addition,
optimal bandwidth scheduling under both UBS and CBS policies are formulated as
constrained convex optimization problems, which are solved by using the
projected subgradient method. Furthermore, the transmission power of the
backhaul system is opportunistically reduced by way of an innovative fixed
power control (FPC) strategy. The notion of backhaul bottleneck occurrence
(BBO) is introduced. An accurate approximate expression of the probability of
BBO is derived, and then verified using Monte Carlo simulations. Several
insights are provided into the offered gains of the proposed schemes through
extensive computer simulations, by studying different aspects of the
performance of super cells including the average sum rate, the BBO probability
and the backhaul power efficiency (PE).Comment: 36 pages, 21 figures, 1 tabl
Transmission lines, quantum graphs and fluctuations on complex networks
High-frequency devices are commonplace and at their foundations often lie cable networks forming fundamental sub-systems with the primary role of transferring energy and information. With increasing demand for ”more electric” systems, the emerging trends in Internet of Things (IoT), as well as the surge in global mobile data traffic, the complexities of the underlying networks become more challenging to model deterministically. In such scenarios, statistical approaches are best suited because it becomes daunting to accurately model details of such networks.
In this thesis, I present a quantum graph (QG) approach of modelling the transfer of energy and information through complex networks. In its own right, the graph model is used to predict the scattering spectrum in wired communications, as well as statistical predictions in wireless communication systems. I derive a more generalised vertex scattering matrix that takes into account cables of different characteristics connected at a common node. This is significant in real applications where different kinds of cables are connected. For example, in digital subscriber line (DSL) networks, the final loop drop may consist of cables with different characteristics.
The proposed graph model is successfully validated both with a Transmission Line (TL) approach, and with laboratory experiments. The model agrees well with the universal predictions of Random Matrix Theory (RMT). In particular, the statistics of resonance is compared with the predictions of Weyl's law, while the level-spacing distribution is compared with the Wigner's surmise, which is a telltale signature of chaotic mixing of the underlying waves.
In addition, I propose an analogue of the so-called random coupling model (RCM), which is important in the study of electromagnetic waves propagating in chaotic cavities. To achieve this, I present a procedure for symmetrising the transfer operator, which we use to modify the QG model in order for it to be comparable to RCM. Unlike the RCM which depends on Gaussian random variables, the graph model works for both Gaussian and non-Gaussian statistics. We use the analogue model to investigate the impact of different boundary conditions on the distribution of energy in networks with different topologies and connectivities.
I further present a novel technique of using quantum graphs to predict the statistics of multi-antenna wireless communication systems. In this context, I present three different ways of calculating the probability density function of Shannon channel capacity. The analytical calculations compare favourably with numerical simulations of networks of varying complexities.
In the area of wired communications, the graph model is used to model the distribution of data in G.fast networks (the fourth-generation Digital Subscriber Line (DSL) networks), using realistic cable parameters from the so-called TNO-Ericsson model. In particular, we show that quantum graph formalism can be used to simulate the in-premises distribution network at G.fast frequencies. The parameters of CAD (or Ba) cables and the in-house distribution network reported in the International Telecommunication Union documentation were used in the simulations
Transmission lines, quantum graphs and fluctuations on complex networks
High-frequency devices are commonplace and at their foundations often lie cable networks forming fundamental sub-systems with the primary role of transferring energy and information. With increasing demand for ”more electric” systems, the emerging trends in Internet of Things (IoT), as well as the surge in global mobile data traffic, the complexities of the underlying networks become more challenging to model deterministically. In such scenarios, statistical approaches are best suited because it becomes daunting to accurately model details of such networks.
In this thesis, I present a quantum graph (QG) approach of modelling the transfer of energy and information through complex networks. In its own right, the graph model is used to predict the scattering spectrum in wired communications, as well as statistical predictions in wireless communication systems. I derive a more generalised vertex scattering matrix that takes into account cables of different characteristics connected at a common node. This is significant in real applications where different kinds of cables are connected. For example, in digital subscriber line (DSL) networks, the final loop drop may consist of cables with different characteristics.
The proposed graph model is successfully validated both with a Transmission Line (TL) approach, and with laboratory experiments. The model agrees well with the universal predictions of Random Matrix Theory (RMT). In particular, the statistics of resonance is compared with the predictions of Weyl's law, while the level-spacing distribution is compared with the Wigner's surmise, which is a telltale signature of chaotic mixing of the underlying waves.
In addition, I propose an analogue of the so-called random coupling model (RCM), which is important in the study of electromagnetic waves propagating in chaotic cavities. To achieve this, I present a procedure for symmetrising the transfer operator, which we use to modify the QG model in order for it to be comparable to RCM. Unlike the RCM which depends on Gaussian random variables, the graph model works for both Gaussian and non-Gaussian statistics. We use the analogue model to investigate the impact of different boundary conditions on the distribution of energy in networks with different topologies and connectivities.
I further present a novel technique of using quantum graphs to predict the statistics of multi-antenna wireless communication systems. In this context, I present three different ways of calculating the probability density function of Shannon channel capacity. The analytical calculations compare favourably with numerical simulations of networks of varying complexities.
In the area of wired communications, the graph model is used to model the distribution of data in G.fast networks (the fourth-generation Digital Subscriber Line (DSL) networks), using realistic cable parameters from the so-called TNO-Ericsson model. In particular, we show that quantum graph formalism can be used to simulate the in-premises distribution network at G.fast frequencies. The parameters of CAD (or Ba) cables and the in-house distribution network reported in the International Telecommunication Union documentation were used in the simulations