Electrical and Electronic Engineering - Theses
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ItemDesign and scheduling of energy-efficient optical communication networks for quality of service provisioning( 2016)Optical networks form the backbone of telecommunications infrastructure and are responsible for providing quality transport service for the aggregate core traffic. The rapid growth in the Internet traffic has led to continuing deployment of additional core network capacity. Higher energy efficiency is an important factor to be considered while scaling up network capacity. In this dissertation, architectures with feasible networking schemes and actionable recommendations towards attaining energy efficiency are proposed. As the main building block of optical transmission, modulation format plays a determining role in the architecture of optical transponder, spectrum allocation as well as lightwave routing and amplification. First, an information theoretic framework is proposed for the performance evaluation of different modulation formats as candidates for future optical networks. A closed form expression is derived for quantifying spectral and energy efficiency of four-dimensional modulation formats for dual-polarization transmission and coherent detection. The analysis demonstrates the advantage of fully utilizing both polarization states from spectral and energy efficiency perspective. Future optical networks will incorporate flexible techniques, namely (i) adaptive modulation and coding, (ii) flexible spectrum allocation, (iii) wavelength conversion, and (iv) traffic grooming. We investigate the problem of energy efficient routing and spectrum allocation in core optical networks incorporating these flexible techniques. We propose a heuristic solution that provides an energy minimized design of long-haul optical networks by avoiding under-utilization of network resources such as optical fibers, transponders and amplifiers. A fixed architecture that does not employ the above mentioned flexible techniques is used as a benchmark for comparison. The numerical results in the west European as well as 24-node US core optical networks show that the energy efficiency of the flexible architecture can outperform the fixed architecture by a significant gap. Finally, optical networks with dynamic traffic are investigated. It is known that the current trend of over-provisioning of capacities in optical networks is not a sustainable approach in the long run. To address this problem, a software defined networking scheme is proposed for quality of service provisioning through energy efficient assignment of optical transponders, employing bandwidth variable distance adaptive modulation and coding. The quality of service measure is defined as the probability of congestion at the core router ports. The proposed scheme enables avoiding over-provisioning of transponder capacity as well as short-term major changes in equipment allocation for networks with dynamic traffic. Seasonal auto-regressive integrated moving average model is employed to forecast the statistics of network traffic for an arbitrary time span based on the requirements and the constraints of the service provider. Numerical results show significant improvements in the energy efficiency of optical networks and reduction in the number of optical lightpaths through the implementation of the proposed technique, compared to the design based on employing conventional fixed optical transponders and no traffic re-routing, where both schemes satisfy the congestion probability requirements.
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ItemOptical wireless integration: network design challenges( 2013)Today, telecommunication networks are expected to provide high bandwidth services to anywhere and at anytime that the services are requested. Among the many solutions available, the optical-wireless converged network has emerged as a popular solution to enable these mandatory features through combining high capacity optical backhaul and flexible wireless access network. However, as the bandwidth demand in the wireless network increases drastically day by day, wireless access technological advances and new requirements continue to evolve. Therefore, to keep pace with the ever advancing wireless access networks and its services, rapid advancements in the optical backhaul network and a tighter integration of optical and wireless access networks are required in order to provide a quality-of-service (QoS) guaranteed ubiquitous access to end users. In particular, numerous challenges need to be addressed in order to deploy optical-wireless converged networks efficiently. These challenges include provisioning adequate backhaul capacities to guarantee QoS of essential services, facilitating efficient intercommunication between base stations to enable traffic diversions and coordination functions, achieving cost-effective deployment and improving energy efficiency of the converged network. This thesis explores efficient solutions to overcome these key challenges. In particular, approaches to achieve cost effective deployments, to guarantee QoS, and to preserve energy efficiency of the converged networks, are investigated. A denser small cell deployment is considered as a future proof solution to cope with the unabated growth of mobile traffic. However, the deployments of small cells are challenging due to the cost associated with the backhaul, powering, and real estate requirements. Therefore, these challenges need to be tackled effectively in order to achieve all the potential benefits of small cell deployments. To this end, this thesis explores cost-effective approaches that leverage the resources associated with the existing fibre infrastructure to provide fibre backhaul for small cells. By analysing the geographic information system (GIS) data of a real network, we show that the existing fibre terminals can be strategically exploited for the small-cell deployment. Moreover, to reduce the dark fibre usage associated with backhauling, we present an approach to select an optimal subset of fibre terminals for small-cell deployments, which yields maximum possible coverage. In addition, to further reduce the total deployment cost of small-cell backhauling, cost-optimal deployment of passive optical networks (PONs) on top of the existing infrastructure is also explored in this thesis. We demonstrate the applicability of our proposed approaches by using them to plan small-cell deployments in a portion of a large carrier's network in the USA. The results reveal that our proposed approaches can save half of the deployment costs associated with small-cell backhauling. Quality-of-service is an essential requirement for next-generation broadband services such as e-Health and Internet protocol television (IPTV). Therefore, in this thesis, we investigate how the characteristics of both optical and wireless networks can be exploited to provide tighter integration and hence, guaranteed QoS in optical-wireless converged networks. In particular, resource handling methods that strategically exploit the frame structures and resource allocation information retrieved from the wireless network to allocate bandwidth in the converged network, are investigated. Moreover, since the direct communication between base stations is identified as one of the major considerations in the next-generation wireless access networks, we investigate how the widely deployed tree topology-based PON can be used to enable these complementary features. To this end, we explore different PON-wireless converged network architectures. In addition, we also investigate an architecture discovery enabled resource allocation mechanism that can be implemented irrespective of the architecture used for the converged network deployment. Our simulation results indicate that the proposed approaches can significantly improve the QoS performance of both the uplink and inter-communications links between base stations. Moreover, as the energy consumption of telecommunication networks is identified as a major contributor towards the global energy consumption, this thesis also explores the energy efficient aspects of the converged networks. The energy consumption of proposed converged network architectures is investigated under various deployment scenarios by analytically modelling the energy consumption of each of the architectures. In addition, we also explore how the energy saving mechanisms can be implemented in the converged network without compromising the QoS. Overall, our studies reported in this thesis, provide insight into deployment strategies that can be used to realise cost-optimal, energy-efficient, and QoS rich next generation optical-wireless converged networks.