Electrical and Electronic Engineering - Theses

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Start date: 2013 × End date: 2019 × Type: PhD thesis × Subject: optimisation × Author: LIN, TAO ×

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    Optimisation of energy efficiency in communication networks
    LIN, TAO ( 2015)
    The mobile data traffic is experiencing unprecedented growth due to the rapid proliferation of devices such as smart phones and tablets. Improving the efficiency of mobile networks, both in terms of traffic flow and energy consumption, is thus critical for sustaining this growing demand. While the adoption of new technologies such as small cell networks and cognitive radio reduces deployment and operational costs, challenges remain regarding how the data traffic can be efficiently processed and transported over the mobile backhaul network. The first aim of this study is to improve the energy efficiency of mobile backhaul networks, while simultaneously balancing the traffic load on its various backhaul nodes, in order to maintain required service quality. First a multi-objective optimisation problem is formulated, then a distributed algorithm is proposed to solve it. The theoretical analysis and numerical simulations demonstrate the results. It is shown that the traffic diurnal cycle poses notable challenges for operators to plan, design and operate mobile backhaul networks so as to achieve desired energy-performance tradeoffs. Continuing growth in cloud-based services and global IP traffic necessitates performance improvements in energy consumption, network delay and service availability. Data centres providing cloud services and transport networks have often multiple stakeholders, which makes it difficult to implement centralised traffic management. The second aim of this study is to apply a game-theoretic approach to data traffic management to obtain a distributed and energy-efficient solution, where each edge router is acting as a strategic player. A multi-objective optimisation problem with a-priori user-specific preferences is formulated for each player and a distributed iterative algorithm is proposed to solve the game. The existence of Nash Equilibrium (NE) of the proposed game is proven followed by the theoretical convergence analysis of the iterative algorithm. The efficiency loss between the strategic game and corresponding global optimisation method is analysed to quantify the impact of selfish behaviour on the overall system performance. Simulation results show notable challenges for operators to plan, design and operate a multimedia content network in order to optimise energy consumption, network delay and load balance over a diurnal cycle. The third aim of this study is to develop an optimisation framework for energy efficiency of optical core networks using Software Defined Networking (SDN). A general system model is proposed where switch-off/sleep mode is introduced to model the power consumption of individual network devices. A multi-objective optimisation problem is formulated by considering system power consumption, server load balance and transport network latency. To demonstrate the problem, a generic Software Defined Networking model is implemented in the Mininet platform by leveraging the OpenFlow protocol. A core network topology is studied in the Mininet framework with various parameter configurations. The simulation results show network topology, traffic diurnal cycle and user Quality of Service (QoS) requirements pose notable challenges for network plan, design and operation so as to achieve the desired energy-performance tradeoffs.